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University Microfilms International 300 N. Zeeb Road Ann Arbor, Ml 48106 8503265 R e ig h a rd , G re g o ry L ynn PHYSIOLOGICAL GENETICS STUDIES OF POPULUS GRANDIDENTATA, POPULUS TREMULOIDES, AND THEIR HYBRID, POPULUS XSMITHII Michigan Staie University University Microfilms International 300 N. Zeeb Road, Ann Arbor, Ml 48106 Ph.D. 1984 PHYSIOLOGICAL GENETICS STUDIES OF POPULUS GRANDIDENTATA, POPULUS TREMULOIDES, AND THEIR HYBRID, POPULUS XSMITHII G r e g o r y Lynn R e i g h a r d A DISSERTATION S ubm itted to M ichigan S t a t e U n i v e r s i t y in p a r t i a l f u l f i l l m e n t o f th e re q u ire m e n ts fo r the d eg ree of DOCTOR OF PHILOSOPHY D epartm ent of F o r e s t r y 1984 ABSTRACT PHYSIOLOGICAL GENETICS STUDIES OF POPULUS GRANDIDENTATA, P. TREMULOIDES, AND THEIR HYBRID, P . XSMITHII BY GREGORY LYNN REIGHARD P opulus tre m u lo id e s grandidentata (tre m b lin g aspen) ( b ig to o th aspen) a r e s y m p a tr ic M ichigan s p e c i e s which o c c a s i o n a l l y h y b r i d i z e . in v estig ated a n d P. th e grow th p o t e n t i a l T his stu d y and p h y s i o l o g i c a l g e n e t i c s o f 206 f a m i l i e s o f P. t r e m u l o i d e s , P. g r a n d i d e n t a t a , and th eir h y b rid , P. X s m i t h i i . b a c k c r o s s e s were a l s o stu d ied T w en ty P. X r o u l e a u i a n a tested . Seven f u l l - s i b f a m i l i e s were u s i n g g a s - e x c h a n g e an d h y d r o p o n i c s y s t e m s t o m e a s u r e photo sy n th esis, p artitio n in g . resp iratio n , In a d d i t i o n , ro o t developm ent, eig h t c u ltu ra l and c a r b o n m ethods fo r p l a n t i n g aspen were e v a l u a t e d . The b e s t p l a n t i n g m e t h o d was p l a c i n g co llars 15 cm b e l o w t h e s o i l em ergent h e r b ic id e , The h e r b i c i d e s d i u r o n and in c o n t r o l l i n g A p r o g e n y t e s t was r e p l i c a t e d to e v a l u a t e grow th p e rfo rm a n c e . l a t i t u d e of p la n ta tio n backcrossed to tre m b lin g weeds. o v e r f i v e M ichigan s i t e s Perform ance of tre m b lin g a s p e n f a m i l i e s was a b o v e a v e r a g e a t a l l w ith site. s i t e s an d i n c r e a s e d P. Xr o u l e a u i a n a h y b r i d s aspen m a le s were s u p e r i o r a t t h e t h r e e Lower P e n i n s u l a root s u r f a c e an d u s i n g t h e p r e - sim azin e. l i n u r o n were n o t e f f e c t i v e the s e e d lin g sites. in g row th M o s t P. Xs m i t h i i f a m i l i e s ha d g r o w t h r a t e s b e l o w t h e m ean. GREGORY LYNN REIGHARD I n i t i a l g r o w t h and s u r v i v a l all p lan tatio n s. o f b i g t o o t h a s p e n was p o o r a t A n a l y s e s o f tw o n e s t e d m a t i n g d e s i g n s showed t h a t g e n e r a l c o m b i n i n g a b i l i t y was p r e s e n t in grow th tra its. Trem bling aspen l e a f e d out e a r l i e r la te r than b ig to o th aspen. in term ed iate. resem bled dieback, H y b r i d p h e n o l o g y was M orphological n o n -ad d itiv e g en etic t r a i t s h a d b o t h a d d i t i v e and variance. the m a te rn a l p arent. bud a b o r t i o n , and d r o p p e d l e a v e s For t h e s e tra its, H ybrids s u f f e r e d and a d v e n t i t i o u s h y b rid s from s h o o t sprouting. Saperda i n o r n a t a and V e n t u r i a t r e m u l a e w e r e t h e m o s t s e r i o u s i n s e c t and d i s e a s e p r o b l e m s , resp ectiv ely . No s i g n i f i c a n t d i f f e r e n c e s w e r e f o u n d f o r p h o t o s y n t h e s i s and d a r k r e s p i r a t i o n a n d P. X s m i t h i i . rates i n t h e two s p e c i e s W h o l e p l a n t p h o t o s y n t h e s i s an d r e s p i r a t i o n were s i g n i f i c a n t l y c o r r e l a t e d w ith l e a f d ry w e ig h t, d r y w e i g h t , and l e a f a r e a . shoot S e e d lin g s w ith high n e t p h o t o s y n t h e t i c r a t e s and l a r g e l e a f a r e a s a s s i m i l a t e d most d ry m a t t e r . r o o t s and l e s s produced the T r e m b l i n g a s p e n p r o d u c e d more p r i m a r y secondary ro o ts than b ig to o th . P. X s m i t h i i s l i g h t l y m o r e p r i m a r y an d s e c o n d a r y r o o t s t h a n e ith e r species. stem r a t i o T r e m b l i n g a s p e n h ad a 50% s m a l l e r than b i g t o o t h . t h e i r m aternal p a r e n ts . H y b r id s had r a t i o s r o o t to sim ilar to DEDICATION To my g r a n d f a t h e r , t h e lifesty le, devotion for a g ric u ltu re late John R e i g h a r d , whose f r u g a l to h ard work, and f o r e s t r y and d e e p a p p r e c i a t i o n i n s p i r e d me t o p u r s u e and u l t i m a t e l y a c h i e v e an e d u c a t i o n in f o r e s t s c i e n c e . ACKNOWLEDGEMENTS I w i s h t o e x p r e s s my s i n c e r e a p p r e c i a t i o n t o Dr. James W. H a n o v e r f o r h i s p a t i e n t g u i d a n c e and s u p p o r t t h r o u g h o u t th is long s t u d y and f o r h i s a c a d e m i c p r o f e s s i o n a l i s m w h i c h h e e x e m p l i f i e d w h i l e s e r v i n g a s my m a j o r p r o f e s s o r . s in c e re g r a titu d e goes to My t h e r e s t o f my g u i d a n c e c o m m i t t e e f o r t h e i r g e n e r o u s a s s i s t a n c e — e s p e c i a l l y Dr. D o n a l d Dick ma nn f o r h i s w i l l i n g n e s s to d is c u s s i d e a s and s h a r e h i s p o p l a r e x p e r i e n c e w i t h me; Dr. B u r t o n B a r n e s f o r h i s m e t i c u l o u s e d i t i n g an d h e l p f u l s u g g e stio n s co n cern in g aspen g e n e c o l o g y ; an d Dr . J a m e s F l o r e for h is tech n ical assistan c e on t h e d e v e l o p m e n t o f a p h o t o s y n t h e t i c s y s t e m and h i s a d v i c e on p r o b l e m s c o n c e r n i n g g a s - e x c h a n g e e x p e r i m e n t a t i o n . I also t h a n k D r. K u r t P r e g i t z e r for s u b s titu tin g for Dr. B a r n e s a t my t h e s i s d e f e n s e and r e v i e w i n g my c h a p t e r s . I e x t e n d my g r a t i t u d e t o Dr. J o n a th a n W right f o r s h a r in g h i s v a s t k n o w l e d g e an d e x p e r i e n c e i n f o r e s t g e n e t i c s w i t h me and h i s w i l l i n g n e s s t o c o n s t r u c t i v e l y c r i t i q u e my i d e a s . I am d e e p l y i n d e b t e d t o t h e e n t i r e MICHCOTIP s t a f f graduate stu d e n ts for th e ir u n se lfish tech n ical assistan c e and e n c o u r a g e m e n t a s w e l l a s warm f r i e n d s h i p d u r i n g study. I am f o r e v e r g r a t e f u l t h a t my p a r e n t s g a v e me w h i l e h eartfelt love, an d th is for the continuous suppport in c o l l e g e . F i n a l l y , my t h a n k s g o e s t o my w i f e , A n g e l a , w h o s e u n e n d i n g patien ce, encouragem ent, an d s u p p o r t — o f t e n own e x p e n s e — c a r r i e d me e m o t i o n a l l y t h r o u g h t h i s a t her stu d y . TABLE OF CONTENTS Page LIST OF TABLES ............................................................................................. LIST OF FIGURES INTRODUCTION vi .......................................................................................... v i i i ................................. 1 CHAPTER 1. E f f e c t s o f C h e m i c a l Weed C o n t r o l and S e e d l i n g P l a n t i n g D e p t h on S u r v i v a l and G r o w t h o f A spen ................. A bstract In tro d u ctio n ................. M a t e r i a l s an d M e t h o d s ............... R esults .......................................................... ..................................................................................... D iscussion L it e r a t u r e C ited ..................................................................... 2. P r o g e n y T e s t i n g o f N a t i v e A s p e n s an d T h e i r H yb rid s f o r Biom ass P r o d u c tio n in M ichigan ....................................................................................... A b stract .............................. In tro d u c tio n M a t e r i a l s and M ethods ...................................................... R e s u l t s an d D i s c u s s i o n .................................................... L i t e r a t u r e C ited .................................................. 3. 6 7 8 12 13 18 20 21 22 25 44 G en etic A nalyses of F i f t e e n P h e n o lo g ic a l, P h y s i o l o g i c a l , an d M o r p h o l o g i c a l T r a i t s i n P o p u l u s g r a n d i d e n t a t a , P . t r e m u l o i d e s , and T h eir H ybrids ....................................................................................... A bstract In tro d u c tio n ............................................................................. M a t e r i a l s and M ethods ...................................................... R e s u l t s and D i s c u s s i o n ......................................... L it e r a t u r e C ited ................................................................... iv 48 49 51 54 74 Page 4. C om parative P h y s io lo g ic a l S tu d ie s o f P h o t o s y n t h e s i s , S h o o t an d R o o t D e v e l o p m e n t , an d Dry M a t t e r P a r t i t i o n i n g i n P o p u l u s g r a n d i d e n t a t a , P. t r e m u l o i d e s , and P. Xs m i t h i i ........................................................................................ A bstract ...................................................................... In tro d u ctio n M a t e r i a l s an d M e t h o d s ...................................................... R e s u l t s an d D i s c u s s i o n .................................................... L i t e r a t u r e C ited ................................................................... CONCLUSIONS AND RECOMMENDATIONS v ............................................... 77 78 79 87 106 108 L IS T OF TABLES Page TABLE 1.1 S o i l p r o p e r t i e s o f t h e Ap h o r i z o n o f t h e 1.2 E f f e c t s o f e i g h t h e r b i c i d e t r e a t m e n t s on weed c o n t r o l , an d a s p e n g r o w t h and s u r v i v a l ........................ 11 y e a r - t o - y e a r c o r r e l a t i o n s o f t h e t r e a t m e n t means f o r h e i g h t and d i a m e t e r o f t h e e x p e r i m e n t a l a s p e n s e e d l i n g s .................................................................................. 13 Tw o-year s u r v i v a l in p e r c e n t f o r asp en t a x a a t t h r e e p l a n t a t i o n s ............................................................................. 26 Two-year g ro w th p e r fo r m a n c e o f t h e b e s t f a m il y and i n d i v i d u a l o f e a c h a s p e n t a x o n a t t h e W a t e r Q u a l i t y p l a n t a t i o n ............................................................................. 28 Biom ass p r o d u c t i o n in d e x ( d i a m e t e r ^ X h e i g h t ) i n % o f p l a n t a t i o n mean f o r f i v e a s p e n t a x a i n f o u r M i c h i g a n p l a n t a t i o n s ......................................................... 29 Number o f f a m i l i e s o f e a c h t a x o n t h a t c o m p r i s e t h e 25 f a m i l i e s w i t h t h e h i g h e s t b i o m a s s p r o d u c t i o n i n d i c e s a t e a c h p l a n t a t i o n .......................... 30 C o r r e l a t i o n s o f tax o n p e rfo rm a n c e (biom ass p r o ­ d u c t i o n i n d e x ) a t e a c h p l a n t a t i o n w i t h mean p e r ­ form ance o f each tax o n fo r a l l p l a n t a t i o n s . ... 31 B i o m a s s p r o d u c t i o n i n d e x i n % o f r e p l i c a t e mean of f a m il i e s - w it h i n - t a x a in r e l a t i o n to th e g e o g r a p h i c d i s t a n c e b e t w e e n p a r e n t s ............................... 38 1.3 2.1 2.2 2.3 2.4 2.5 2.6 fie ld .. 9 2.7 Age-age c o r r e l a t i o n s o f t h e mean f a m i l y h e i g h t i n t h e n u r s e r y w i t h t h e mean f a m i l y h e i g h t a v e r a g e d o v e r f o u r p l a n t a t i o n s ................................................................... 42 3.1 L e a f f l u s h , l e a f f a l l , an d l e a f a r e a d u r a t i o n in p e r c e n t o f r e p l i c a t e mean a t t h e E a s t L a n s i n g p l a n t a t i o n f o r t h e e a r l i e s t and l a t e s t p h e n o l o g i c a l f a m i l i e s o f P. t r e m u l o i d e s , P. g r a n d i d e n t a t a , P. X s m i t h i i , and P. X r o u l e a u i a n a b a c k c r o s s e s . . . . 55 3.2 P henology d i f f e r e n c e s in p e r c e n t o f r e p l i c a t e mean o f t r e m b l i n g and b i g t o o t h a s p e n h a l f - s i b f a m i l i e s from d i f f e r e n t l a t i t u d i n a l r e g i o n s in M i c h i g a n a t t h e E a s t L a n s i n g p l a n t a t i o n .................. vi 59 Page 3.3 3.4 3.5 3.6 4.1 4.2 4.3 4.4 4.5 C o rre la tio n s of th re e phenological t r a i t s of h a l f - s i b , f u l l - s i b , an d c o m b i n e d t r e m b l i n g and b ig to o th aspen f a m ilie s w ith th e l a t i t u d i n a l o r i g i n o f t h e i r p a r e n t s ........................................... 61 C o r r e l a t i o n s o f tw o -y e a r grow th p erfo rm an ce ( d i a m e t e r 2 x h e i g h t ) o f 179 b i g t o o t h , t r e m b l i n g , and h y b r i d a s p e n f a m i l i e s a t e a c h p l a n t a t i o n w ith t h e i r r e s p e c tiv e p h en o lo g ical t r a i t s r e c o r d e d a t t h e E a s t L a n s i n g p l a n t a t i o n ..................... 62 Mean r a n k s f r o m F r i e d m a n ' s t w o - w a y c l a s s i f i c a t i o n t e s t f o r s i x m o r p h o l o g i c a l and p h y s i o l o g i c a l c h a r a c t e r s m e a s u r e d i n 206 a s p e n and h y b r i d a s p e n f a m i l i e s a t t h e E a s t L a n s i n g p l a n t a t i o n ..................... 64 S u s c e p t i b i l i t y to V e n tu ria tre m u la e in p e r c e n t o f t h e p l a n t a t i o n mean f o r e a c h s p e c i e s an d h y b r i d a t t h e S i x L a k e s p l a n t a t i o n ................................................... 69 P h o t o s y n t h e s i s , r e s p i r a t i o n , l e a f a r e a , an d p l a n t d r y w e i g h t d a t a from t h e f o u r a s p e n t a x a i n t h e p h o t o s y n t h e s i s s t u d y .................................................... 88 S h o o t and r o o t m e a s u r e m e n t s o f t h e f o u r a s p e n t a x a f r o m t h e h y d r o p o n i c s t u d y a f t e r week 5 . . . . 93 C o r r e l a t i o n s b e t w e e n l e a f a r e a and p l a n t d r y w e i g h t o f a s p e n s e e d l i n g s grow n i n t h e h y d r o ­ p o n i c s y s t e m .......................................................................................... 96 Mean g r o w t h d a t a o f 40 s e e d l i n g s f o r e a c h o f f o u r a s p e n t a x a g r o w n i n t h e n u r s e r y f o r o n e y e a r . .. 103 Mean p h e n o l o g y d a t a o f 40 s e e d l i n g s f o r e a c h o f f o u r a s p e n t a x a g row n i n t h e n u r s e r y ............................. 104 v ii LIST OF FIGURES Page FIGURE 4 .1 4.2 4 .3 S chem atic diag ram of th e p l a n t g a s-e x c h a n g e sy stem used in th e p h o t o s y n t h e s i s s tu d y . ... W eekly a p i c a l l e a f p r o d u c t i o n o f h y d r o p o n i c a l l y - g r o w n a s p e n an d a s p e n h y b r i d s ..... 94 W eekly h e i g h t i n c r e m e n t o f h y d r o p o n i c a l l y gro w n a s p e n and a s p e n h y b r i d s .............................. 95 4 .4 W eekly p r i m a r y r o o t g ro w th o f h y d r o p o n i c a l l y 97 gr ow n a s p e n an d a s p e n h y b r i d s .............................. 4.5 Weekly s e c o n d a r y r o o t p r o d u c t i o n o f h y d r o p o n i c a l l y - g r o w n a s p e n and a s p e n h y b r i d s . .... 4 .6 Number o f s e c o n d a r y r o o t s p e r cm o f p r i m a r y r o o t o f h y d r o p o n i c a l l y - g r o w n a s p e n and a s p e n h y b r i d s ....................................................................................... 100 4.7 C o m p arativ e carb o n p a r t i t i o n i n g betw een t h e r o o t s , s t e m , an d l e a v e s o f h y d r o p o n i c a l l y gro w n a s p e n an d a s p e n h y b r i d s ............................... 101 v ii i 82 99 INTRODUCTION T rem bling aspen b igtooth aspen (P o p u l u s t r e m u l o i d e s (P. g r a n d i d e n t a t a s p e c i e s th ro u g h o u t M ichigan. sp ecies is M ichx.) in f r e q u e n t under n a t u r a l tim es and P r e g i t z e r species, (H eim burger 1936, an d B a r n e s 1 9 8 0 ) . an d b i g t o o t h a s p e n ( F o w e lls 1965). site s co n d itio n s because of to d if f e r e n c e s P a u le y 1956, B a r n e s 1961, T rem bling aspen e x p l o i t s a w ider range of trem bling w ith both s p e c ie s , aspen (Graham e t a l . b ig to o th 1963). ( D a v i d s o n and H o w e v e r , b i g t o o t h a s p e n i s much l e s s su scep tib le to H ypoxylon c a n k e r which c a u s e s t h e l a r g e s t annual (8.5 m i l l i o n cu b ic m eters) th e Lake S t a t e s (M arty 1972). sto ck lo ss in g enetic v a ria tio n (1969), al^. o f a sp e n grow ing Abundant n a t u r a l in p h en o lo g y , m orphology, p h y s io lo g y , wood p r o p e r t i e s h a s b e e n f o u n d B uijtenen ^ t (1959), E inspahr C h e l i a k and D an cik aspen has a l s o been r e p o r te d v ariatio n and in t r e m b l i n g a sp en by van (1982), an d B e n s o n (1967), Barnes an d many o t h e r s . A l t h o u g h much l e s s s t u d i e d t h a n t r e m b l i n g a s p e n , genetic in Trem bling aspen i s a b o r e a l Many d i s e a s e s a n d i n s e c t s a t t a c k b o t h s p e c i e s P r e n t i c e 1968). sym patric i s a te m p e ra te m esic s p e c ie s i n M i c h i g a n , b u t on s i t e s aspen outcom petes are an d H y b r i d iz a t io n betw een th e prezygotic is o la tio n b a r r ie r s a ttrib u te d flow ering M ic h x . ) big to o th to h a v e l a r g e am ounts o f (B arnes 1969, Okafo 1976). T r e m b l i n g and b i g t o o t h a s p e n a r e t h e m o s t i m p o r t a n t pulpwood s p e c i e s i n M i c h i g a n ( B l y t h and S m i t h 1 9 8 2 ) . prod u ctio n of n a tu r a l Volume s t a n d s a t a g e 50 h a s b e e n r e p o r t e d 1 to 2 b e a s h i g h a s 52 a n d 53 c o r d s p e r a c r e f o r t r e m b l i n g a n d b ig to o th aspen, th is resource d evelops resp ectiv ely is ( P e r a l a 1977). The demand f o r in c re a sin g as the f o r e s t p ro d u c ts in d u stry new t e c h n o l o g i e s t o u s e a s p e n f o r p r o d u c t s p articleb o ard , o rie n te d -stran d other tra d itio n al than th e board, pu lp , fla k eb o ard , paper, com m unication). etc.) and m a t c h s t i c k s . T h e r e a r e now a d i s p r o p o r t i o n a t e nu m b er o f o l d , asp en s ta n d s in M ichigan (ie ., lo w -q u ality (James W adsw orth, p e r s o n a l To s u p p l e m e n t t h e n a t i v e a s p e n r e s o u r c e , P a c k a g in g C o r p o r a t i o n o f Am erica i s p l a n t i n g h y b r i d p o p l a r s in s h o r t - r o t a t i o n fib e r p la n ta tio n s. The u s e o f a s p e n s in t h e s e p l a n t a t i o n s h as been a v o id e d becau se g e n e t i c a l l y i m p r o v e d p l a n t i n g s t o c k i s n o t r e a d i l y a v a i l a b l e an d e co n o m ical e s t a b l i s h m e n t p r o c e d u re s h a v e y e t to be adeq u ately developed. To h e l p r e s o l v e t h e s e e c o n o m i c a l l y - b a s e d p r o b l e m s , t h i s s t u d y had t h r e e p r i m a r y o b j e c t i v e s . to fin d a p l a n t i n g The s e c o n d o b j e c t i v e was t o stock. v ariatio n ex ists o ld -field site s. im prove th e germ plasm b a se Even th o u g h e x t e n s i v e n a t u r a l i n M i c h i g a n p o p u l a t i o n s o f t r e m b l i n g and b ig to o th aspen, g e n e tic gain u n til in grow th r a t e c a n n o t occur th e s p e c i e s h av e been progeny t e s t e d . h alf-sib and f u l l - s i b superior p aren ts, o b j e c t i v e was s y s t e m b a s e d on h e r b i c i d e s w h i c h w o u l d s u c c e s s f u l l y e s t a b l i s h a s p e n on of the p la n tin g The f i r s t A com bination p r o g e n y t e s t was i n i t i a t e d fam ilies, and i n d i v i d u a l s . t h e two s p e c i e s w e r e h y b r i d i z e d to id en tify F u rth erm o re, i n an a t t e m p t t o in co rp o rate 3 H y p o x y l o n mamma turn r e s i s t a n c e increase the s i t e into trem bling aspen, ad ap tab ility of b ig to o th asp en , to d i v e r s i f y th e breeding p o p u la tio n , a d d itiv e genetic reported h y b rid s varian ce to an d t o g e n e r a t e (heterosis) t h e non­ w hich has been in grow th r a t e s of w h ite p o p l a r x b i g t o o t h aspen (H all The t h i r d et jil. 1982). o b j e c t i v e was t o q u a n t i f y t h e a m o u n t o f a d d i t i v e and n o n - a d d i t i v e g e n e t i c v a r i a n c e s p e c i e s an d t o d e t e r m i n e how t h e s e were e x p r e s s e d in th e h y b r id i n t h e tw o types of g e n e tic variance (P o p u l u s X s m i t h i i B o i v i n ) . F i e l d m e a s u r e m e n t s an d c o n t r o l l e d - e n v i r o n m e n t s t u d i e s u s i n g g a s - e x c h a n g e and h y d r o p o n i c s y s t e m s w e r e u s e d t o m e e t t h i s o b jectiv e. 4 LITERATURE CITED B a r n e s , B.V. 1961. H y b r i d a s p e n s i n t h e Lower P e n i n s u l a M ichigan. Rhodora 6 3 :3 1 1 -3 2 4 . of B a r n e s , B.V. 1 9 69. N a t u r a l v a r i a t i o n an d d e l i n e a t i o n o f c l o n e s o f P o p u l u s t r e m u l o i d e s and P. g r a n d i d e n t a t a i n N o r t h e r n Lower M i c h i g a n . S ilv a e G enetica 18:130-142. B l y t h , J . E . an d W.B. S m i t h . 1982. La ke S t a t e s b y c o u n t y , 1 981 . S t a . R es. Note NC-287. 4 p p . Pulpwood p r o d u c t i o n in th e N orth C e n t r a l For. Expt. C h e l i a k , W.M. an d B.P. D a n c i k . 1 982. G enic d i v e r s i t y of n a t u r a l p o p u la tio n s of a clo n e-fo rm in g t r e e Populus trem u lo id es. Can. J . G en et. C y t o l . 2 4 :6 1 1 -6 1 6 . D a v i d s o n , A.G. an d R.M. P r e n t i c e . 1968. I n s e c t s and d iseases. I N / G r o w t h and U t i l i z a t i o n o f P o p l a r s i n C a n a d a . J .S . M a in i and J.H . C a y f o r d ( e d . ) . D e p t, o f F o r e s t r y a n d R u r a l D e v e l o p m e n t . O t t a w a , O n t. D e p t . P u b l . No. 1 2 0 5 . p p . 1 1 6 - 1 4 4 . E i n s p a h r , D.W. an d M.K. B e n s o n . 1967. G eographic v a r i a t i o n o f q u a k i n g a s p e n i n W i s c o n s i n an d U p p e r M i c h i g a n . S ilvae G en etica 16:106-112. F o w e l l s , H.A. S tates. 1965. S i l v i c s of F o r e s t T rees o f th e U nited USDA A g r i c . Hdbk. No. 2 7 1 . 762 p p . G r a h a m , S . A . , R.P . H a r r i s o n , J r . , a n d C.E. W e s t e l l , J r . 1963. A spens: P hoenix T re e s o f t h e G r e a t Lakes R egion. Univ. o f M i c h i g a n P r e s s , Ann A r b o r , M i c h i g a n . 272 p p . H a l l , R . B . , G.D. H i l t o n , a n d C.A. M a y n a r d . 1982. C o n stru c­ t i o n lum ber from h y b r i d a sp e n p l a n t a t i o n s i n t h e C e n t r a l S tates. J . F o r. 80:291-294. H e i m b u r g e r , C.C. 1 9 3 6 . R e p o r t on p o p l a r F o re stry C h ro n icle 12:285-290. h y b rid izatio n . M a r t y , R. 1 9 72. The e c o n o m i c i m p a c t o f H y p o x y l o n c a n k e r on t h e Lakes S t a t e s r e s o u r c e . I N / A s p en Symp. P r o c . , USDA F o r . S e r v . G e n . T e c h . R e p . NC-1. pp. 21-26. O k a f o , A.O. 1976. C o m p a r a t i v e p h y s i o l o g y an d d e v e l o p m e n t o f t r e m b l i n g a s p e n (P o p u l u s t r e m u l o i d e s M ic h x .) and b i g t o o t h a s p e n (P o p u l u s g r a n d i d e n t a t a M ic h x . ) f r o m M i c h i g a n p o p u l a t i o n s . P h . D . T h e s i s , M i c h i g a n S t a t e U n i v . 103 p p . P a u l e y , S.S. 1 9 56. N atural h y b rid iz a tio n of th e U n i v . M i n n e s o t a F o r e s t r y N o te 4 7 . 2 p p . aspens. 5 P e r a l a , D.A. 1 9 77. M an ag er's handbook f o r asp en in th e N orth C entral S ta te s. USDA F o r . S e r v . Ge n. T e c h . Rep . N C -3 6 . 30 p p . P r e g i t z e r , K.S. an d B.V. B a r n e s . 1980. F low ering phenology o f P o p u l u s t r e m u l o i d e s an d P. g r a n d i d e n t a t a an d t h e p o t e n t i a l f o r h y b r i d i z a t i o n . Can. J . F o r . R es. 1 0 :2 1 8 -2 2 3 . V an B u i j t e n e n , J . P . , D.W. E i n s p a h r , a n d P.N. J o r a n s o n . 1959. N a t u r a l v a r i a t i o n in P o p u l u s t r e m u l o i d e s M ichx. Tappi 42:819-823. CHAPTER 1 EFFECTS OF CHEMICAL WEED CONTROL AND SEEDLING PLANTING DEPTH ON SURVIVAL AND GROWTH OF ASPEN (A ccepted f o r P u b l i c a t i o n in Tree P l a n t e r s ' N otes) ABSTRACT E ight c u l t u r a l tre a tm e n ts in v o lv in g preem ergent herb icid es and p l a n t i n g d e p t h w e r e t e s t e d a s p e n g r o w t h an d s u r v i v a l . placing the ro o t c o l l a r i n j u r y from s i m a z i n e . f o r e f f e c t s on D e e p - p l a n t i n g a s p e n s e e d l i n g s by 15 cm b e l o w t h e s o i l s u rf a c e reduced S i m a z i n e g a v e e x c e l l e n t weed c o n t r o l , w h e r e a s d i u r o n an d l i n u r o n w e r e n o t a s e f f e c t i v e . Non- l e t h a l h e r b i c i d e dam a g e t h a t a f f e c t e d e a r l y s e e d l i n g g r o w t h became i n s i g n i f i c a n t a s t h e t r e e s grew o l d e r . Therefore, s u r v i v a l was m o re i m p o r t a n t t h a n e a r l y g r o w t h a s a c r i t e r i o n for e v a lu a tin g h erbicides fo r aspen e s ta b lis h m e n t. 6 7 INTRODUCTION Spawned b y t h e e n e r g y c r i s i s in terest in s h o r t - r o t a t i o n of the tree p lan tatio n s p ro d u ctio n co n tin u es t o gr o w . freq u en t choices for these p la n ta tio n s because of th e ir 7 0 's, research fo r biom ass S pecies o f P opulus a re in t h e Lake S t a t e s f a s t g r o w t h and c o p p i c i n g a b i l i t y . th e ir p o p u larity , i n e x p e n s i v e means o f p l a n t a t i o n e s t a b l i s h m e n t a r e l a c k i n g f o r m ost P o p u lu s s p e c i e s . p o p lars, cottonw ood, hardwood s p e c i e s , co n tro l e ffectiv e, p rep aration and weed 2-3 y e a r s in o r d e r to be s u c c e s s f u l l y on a b a n d o n e d f i e l d s but expensive. a l t e r n a t i v e m ethod t h a t i s risk y . Hybrid and a s p e n , a l o n g w i t h m o s t o t h e r n e e d good s i t e in th e f i r s t esta b lish ed D espite (4, 1 3 , 14). C u ltiv atio n C h e m i c a l weed c o n t r o l le s s expensive, is i s an but i t i s m o re Improved p l a n t i n g p r a c t i c e s t h a t i n c l u d e c h e m ic a l weed c o n t r o l and e x c l u d e c u l t i v a t i o n n e e d t o b e d e v e l o p e d and r e f i n e d fo r a l l p o p la r s p e c ie s , e s p e c i a l l y the s e n s i t i v e b a l s a m p o p l a r s and a s p e n s . Much o f t h e p r e v i o u s p o p l a r r e s e a r c h c o n c e r n i n g preem ergent h e r b i c i d e s has been d i r e c t e d (S ection A igeiros) , balsam p o p la r s t h e i r hyb rid s. at th e cottonw ood ( S e c t i o n T a c a m a h a c a ) , and H e r b i c i d e r e s e a r c h on a s p e n (P o p u l u s g r a n d i d e n t a t a M ic h x . a n d j?. t r e m u l o i d e s M i c h x . o f S e c t i o n L euce), how ever, has been lim ite d . a b u n d a n t and r e g e n e r a t e e a s i l y t h e r e has been l i t t l e Since aspens a re from e s t a b l i s h e d past in te re st in p l a n t i n g stands, them . t h e r e c e n t u p s u r g e o f r e s e a r c h on e n e r g y p l a n t a t i o n s , W ith aspens 8 a r e now b e i n g c o n s i d e r e d as a p o s s i b l e p l a n t a t i o n The work r e p o r t e d h e r e t e s t e d preem ergent h e r b ic id e s , sim azine (eth y la m in o )-s-triazin e), 1 ,1 -d im eth y lu rea), and m ethoxy-l-m ethylurea) abandoned f i e l d diuron lin u ro n species. th e e f f ic a c y of the (2 -ch lo ro -4 ,6 -b is (3 -(3 ,4 -d ich lo ro p h en y 1)- (3-(3,4 -d ic h lo ro p h e n y 1 )-1 - i n c o n t r o l l i n g weed c o m p e t i t i o n on an in s o u th e r n M ichigan. These h e r b i c i d e s have been used p r e v i o u s l y in p o p l a r p l a n t a t i o n s by numerous scie n tists von A l t h e n (6), in clu d in g and N e t z e r and N o s te h erb icid es, (8 ). 14), Dickmann, e t a l . In c o n ju n c tio n w ith these d e e p - p l a n t i n g o f t h e s e e d l i n g s and t h e u s e o f p l a s t i c m ulch were e v a l u a t e d in ju ry . (11, f o r p r o t e c t i o n from c h e m i c a l The p u r p o s e o f t h e s e t r e a t m e n t s was t o sy ste m u s in g c h e m i c a l s t h a t c o u l d be a p p l i e d a s p e n s on a b a n d o n e d f a r m l a n d fin d a to p l a n t i n g in M ic h ig a n . MATERIALS AND METHODS An a g r i c u l t u r a l fie ld t h a t h a d b e e n i d l e f o r 25 y e a r s was c h o s e n a s a p l a n t i n g s i t e . In gham C o u n t y (S 6 T3N R1W), a M a r l e t t e f i n e san d y loam , G lossoboric H ap lu d alf. The f i e l d M ichigan. The s o i l is c la s s if ie d The s o i l i s l o c a t e d in series, as a m ixed, m esic p r o p e r t i e s an d c h e m i s t r y o f t h e Ap h o r i z o n w e r e a n a l y z e d b y t h e M i c h i g a n S t a t e U niv ersity S o il T estin g L aboratory (tab le 1.1). The f i e l d was mowed i n S e p t e m b e r , 1980 and s p r a y e d w i t h s e v e n liters/h ectare gly p h o sate in o n e-m eter s t r i p s . The m a j o r v e g e t a t i o n c o v e r a t t h e t i m e o f s p r a y i n g was q u a c k g r a s s (A g r o p y r o n repens L. B eauv.). 9 T able 1.1. S oil p r o p e r t i e s o f t h e Ap h o r i z o n o f t h e f i e l d . S oil S eries T exture (C lass) M arlette F in e Sandy Loam Sandy Clay Loam O rganic M a t t e r (%) 2.0 C a tio n Exchange C a p a c i t y (meq/g) Clay (%) PH 21.3 6.7 6 N ursery-grow n, 1-0 s e e d l i n g s of b ig to o th g ran d id en tata M ichx.) and q u a k i n g a s p e n t h a t had b e e n l i f t e d refrig era te d p lo ts M ic h x . ) aspen (P o p u l u s (P o p u l u s t r e m u l o i d e s in M arch and s t o r e d in a room w e r e p l a n t e d May 8 , 1981 i n 5 - 7 t r e e in a random ized b l o c k d e s ig n w ith s e v e n r e p l i c a t i o n s . The t r e e s rows. were sp aced 1.2 m w i t h i n There were e i g h t p l o t s ro w s and 2.4 m b e t w e e n (treatm en ts) per rep lic atio n . Ea ch p l o t c o n t a i n e d b o t h s p e c i e s an d was r a n d o m l y a s s i g n e d one o f e i g h t p o s s i b l e (2 .8 k g / h a a.i.) for treatm en ts a ll chem ical a rb itra ry co n cen tratio n th a t f e l l ap p licatio n rates (ta b le 1.2). treatm en ts was an w ith in th e low er range of c o m m o n ly u s e d f o r the three h erb icid es. O ptim al h e r b i c i d e d o s e a g e s were n o t t e s t e d . procedures co n sisted The d o s e a g e o f m aking a s l i t P lan tin g down e a c h s p r a y e d row w ith a t r e e p l a n t e r and th e n hand p l a n t i n g t h e t r e e s in th e slit. The r o o t c o l l a r s o f a l l trees in each t r e a t m e n t p l o t w e r e p l a c e d e i t h e r 3 o r 15 cm b e l o w t h e s o i l s u r f a c e . one t r e a t m e n t , around each In a 3 0 - c m - s q u a r e b l a c k p l a s t i c m u l c h was p l a c e d tree. On May 1 2 t h , a l l p l o t s to r e c e iv e a h e r b ic id e tre a tm e n t w e r e c o m p l e t e l y s p r a y e d u s i n g a 9. 5 l i t e r L o fstran d ( M odel 10 1730) h a n d s p r a y e r The c o n t r o l t h a t had been c a l i b r a t e d p l o t s were hand c u l t i v a t e d . at Rain o n t h e t e s t s i t e f r o m May 1 0 t h t o May 1 5 t h . normal A pril (1 8.5 cm)f o r (1982) all May an d J u n e o f 30-40 PSI. (7.6 cm) f e l l R a i n f a l l was 1 9 81. The f o l l o w i n g p l o t s were s p ra y e d w ith 2.8 k g / h a a . i . sim azine. One m o n t h a f t e r (ta b le the 1.2) o f h e r b i c i d e Septem ber of 1981, 1981 s p r a y i n g , a s u b j e c t i v e r a t i n g injury tree in th e f a l l recorded Percent for a l l su rv iv al In fo r each p l o t . o f 1 9 8 1 , 1 9 8 2 , an d D i a m e t e r s a t 5 cm a b o v e g r o u n d l e v e l 1982 an d 1 9 83. was t a k e n . weed c o n t r o l was e v a l u a t e d T ree h e i g h t s were m easured 1 9 83. to each fo r each were m easured in t r e a t m e n t was th reeyears. A n a l y s i s o f v a r i a n c e was p e r f o r m e d on p l o t m eans f o r each t r a i t ex cep t s u r v i v a l an d weed c o n t r o l . H erbicide damage r a t i n g s were t e s t e d for n o rm ality before a n a ly s is . The s u r v i v a l an d weed c o n t r o l d a t a w e r e n o t n o r m a l l y d i s t r i ­ b uted, so F r ie d m a n 's tw o - w a y c l a s s i f i c a t i o n used to d e t e c t d i f f e r e n c e s . t r e a t m e n t means f o r data. test An LSD t e s t was a p p l i e d to the t h e 1981 h e i g h t an d h e r b i c i d e dam a g e C o r r e l a t i o n s betw een y e a r s were g e n e r a t e d t r e a t m e n t m eans o f h e i g h t an d d i a m e t e r . rank c o r r e l a t i o n s were c a l c u l a t e d weed c o n t r o l (10) was for N on-param etric, for th e r e l a t io n s h i p of t o t h e t r e a t m e n t m ean s f o r h e i g h t an d d i a m e t e r . Table 1 .2 . E f f e c t s o f e i g h t h e r b i c i d e t r e a t m e n t s on weed c o n t r o l , and a s p e n g r o w t h and s u r v i v a l . Treatm ents Chemical H erbicide (2.8 kg/ha) P hytotoxicity P lanting Dep th (3 o r 15 cm) Sim azine Sim azine Simazine Diuron Diuron Linuron Linuron None LSD ( . 0 5 ) S ignificance of F -value Regular Deep Regular Regular Deep Regular Deep Regular Other P l a s t i c Mulch C ultivated Growth D a t a ( T r e a t m e n t Means) H erbicide Weed 1981 1983 1983 1983 I n j u r y 1 C o n t r o l 2 S u r v i v a l H e i g h t H e i g h t Diameter-* (aspen) (m) (m) (cm) (%) (%) .6 7 .12 .6 5 .69 .7 2 1.23 .92 .00 87 89 82 59 56 62 62 100 62 89 79 77 71 55 61 98 .6 7 .72 .7 4 .76 .75 .69 .7 3 .90 2.7 3.0 2.7 2.9 3.2 2.8 3.1 3.4 3.1 3.5 3.2 3.5 3.5 3.1 3.4 4.0 .3 5 ** ** * .1 3 * n .s. n .s. ^ I n j u r y r a t i n g w as: 0 = no dam ag e; 1 = y e l l o w l e a v e s ; and 2 = y e l l o w and b l a c k l e a v e s . ^ P e r c e n t o f sp ra y e d ground w ith o u t l i v e weeds. ■^Diameter a t 5 cm a b o v e g r o u n d s u r f a c e . * /* * S i g n i f i c a n t a t t h e 5 and 1 p e r c e n t l e v e l s , r e s p e c t i v e l y . 12 RESULTS The c o n t r o l an d o n e s i m a z i n e had th e l e a s t h e r b i c i d e (ta b le 1.2). in itia l h e r b i c i d e damage. chem ical treatm ent i n j u r y an d t h e b e s t weed c o n t r o l The two l i n u r o n than e i t h e r d iuron or (deep-planting) t r e a t m e n t s had th e m ost S i m a z i n e g a v e b e t t e r weed c o n t r o l lin u ro n . D e e p -p la n tin g reduced i n j u r y on s i m a z i n e p l o t s b u t n o t on t h e d i u r o n o r lin u ro n p lo ts . The c o n t r o l t r e a t m e n t had t h e h i g h e s t s u r v i v a l of th e th re e y e a rs. One s i m a z i n e a l s o h a d good s u r v i v a l . o th e r sim azine su rv iv al. (deep-planting) (reg ular-planting ) tre a tm e n t gave poor D e e p - p l a n t i n g i n c r e a s e d s u r v i v a l on s i m a z i n e m o rtality occurred a f t e r the f i r s t y ear; L ittle th erefo re, the ra n k in g s o f th e t r e a t m e n ts rem ained unchanged throughout the F irst-, were g r e a t e s t p lan tin g ) treatm ent The two l i n u r o n t r e a t m e n t s and one p l o t s b u t n o t on t h e d i u r o n and l i n u r o n p l o t s . su rv iv al in each th ree second-, years. an d t h i r d - y e a r h e i g h t s an d d i a m e t e r s in t h e c o n t r o l p lo ts. The s i m a z i n e (reg u lar- t r e a t m e n t g e n e r a l l y g a v e t h e p o o r e s t h e i g h t and d ia m e te r grow th. I n t h e s e c o n d an d t h i r d y e a r s , p la n te d p l o t s of sim azin e, diuron, than th e r e g u l a r l y - p l a n t e d p l o t s . the deep- and l i n u r o n g r e w m or e T h i s t r e n d was a l s o t r u e f o r d i a m e t e r e x c e p t t h e r e w e r e no d i a m e t e r d i f f e r e n c e s the d iu ro n p l o t s for the th ir d year. The s e e d l i n g s in that w e r e d e e p - p l a n t e d a p p e a r e d t o s u f f e r no d e t r i m e n t a l p h y s i o l o g i c a l e f f e c t s from t h e p l a c e m e n t of t h e r o o t c o l l a r 13 15 cm b e l o w t h e s o i l Benson surface. (4) who r e p o r t e d This o b s e r v a tio n th at deep-plantin g agreed w ith a s p e n 10 t o 30 cm a b o v e t h e r o o t c o l l a r d i d n o t c r e a t e a n y a d v e r s e esta b lish m en t effects. T r e a t m e n t m e a n s f o r h e i g h t and d i a m e t e r w e r e s i g n i f i c a n t l y c o r r e la te d a t the 1 p e rc e n t l e v e l betw een years 1 9 8 1 - 8 2 and 1 9 8 2 - 8 3 an d a t t h e 5 p e r c e n t l e v e l years 1981 an d 1983 (ta b le 1.3). c o r r e l a t i o n s b e t w e e n weed c o n t r o l l o w ( r= .05 t o le v e l .20) N on-param etric, for rank and t h e g ro w th d a t a were and n o n - s i g n i f i c a n t at th e 5 percent of p r o b a b i l i t y . T able 1 .3 . Y e a r - t o - y e a r c o r r e l a t i o n s o f th e t r e a t m e n t means f o r h e i g h t an d d i a m e t e r o f t h e e x p e r i m e n t a l a s p e n seed lin g s. Y ears C o r r e la te d H eight D iam eter 1981 w i t h 1982 1 981 w i t h 1983 1982 w i t h 1983 . 84 ** .77 * . 9 7 ** . 9 5 ** * / ** S i g n i f i c a n t a t t h e 5 a n d 1 p e r c e n t l e v e l s , r e s p e c t i v e l y . 1D e g r e e s o f f r e e d o m = 7. DISCUSSION T h r e e - y e a r r e s u l t s o f h e i g h t an d d i a m e t e r g r o w t h f o r each tre a tm e n t in d ic a te d t h a t c u l t i v a t i o n a l o n e was s u p e rio r to a l l treatm en ts, chem ical became i n s i g n i f i c a n t a f t e r s m a l l e r an d l e s s the f i r s t but the d if f e r e n c e s grow ing s e a so n . sig n ifican t c o rre la tio n (tab le 1.3) The of th e 14 t r e a t m e n t m e a n s f o r h e i g h t b e t w e e n y e a r s 1981 a n d 1983 ind icate th at first-y e a r d e c re a sin g w ith treatm ent tim e; increased e.g., attrib u ted treatm ent i n g r o w t h an d s u r v i v a l t o 79% (1983) (tab le 1.2). poorest of the The i n i t i a l of c u l t i v a t e d so il from th e c h e m ic a l t r e a t m e n t s , t r e e s was as w e l l as aeratio n . Sim azine, d iu ro n , s p e c ie s o f P opulus a t and l i n u r o n a r e t o x i c t o s e n s i t i v e low c o n c e n t r a t i o n s . means o f u p t a k e o f t h e s e c h e m i c a l s Jaciw of th e t o t h e a b s e n c e o f b o t h weed c o m p e t i t i o n and phytotoxic e f f e c ts increased t h e mean h e i g h t f r o m 74% (1981) mean h e i g h t f o r t h e b e s t su p erio rity t r e a t m e n t d i f f e r e n c e s were (personal com m unication) The p r i n c i p a l i s by r o o t a b s o r p t i o n . observed in O n ta rio t h a t d e e p - p l a n t e d w h i t e p o p l a r - a s p e n h y b r i d s w e r e n o t dam ag ed by sim azine. T herefore, av o id an ce o f h e r b ic id e c o n ta c t w ith th e r o o t system is e s s e n t i a l sen sitiv e species for e s ta b lis h in g chem ical- such as th e n a t i v e R o a d h o u s e and B i r k aspens. (9) f o u n d t h a t s i m a z i n e a p p l i e d a t a r a t e o f 2.2 k g / h a a . i . on a c u l t i v a t e d fie ld did not p e n e t r a t e b e l o w t h e t o p 15 cm o f s o i l d u r i n g t h e f i r s t grow ing s e a so n . In a d d i t i o n , W e l d o n an d Timmons (15) s h o w e d on a s a n d y c l a y l o a m a n d a l o a m y s a n d s o i l t h a t d i u r o n , when a p p l i e d a t r a t e s o f 2.2 an d 4 .5 k g / h a a . i . , d o e s n o t p e n e t r a t e b e l o w 10 cm i n t h e s o i l t h e amount o f irrig atio n used. r e g a r d le s s of These f i n d i n g s suggest d e e p - p l a n t i n g o f a s p e n s e e d l i n g s 15 cm b e l o w t h e s o i l s u r f a c e s h o u ld m inim ize h e r b i c i d e c o n t a c t w ith th e r o o t th at 15 system . The s i m a z i n e The o n e s i m a z i n e su rv iv al o ther after sim azin e resu lts here support th is h ypothesis. (deep-planting) t r e a t m e n t h a d 89 p e r c e n t t h r e e y e a r s c o m p a r e d t o 62 p e r c e n t f o r t h e (reg u lar-p lan tin g ) The r e a s o n s for the treatm en t. fa ilu re o f t h e d i u r o n an d l i n u r o n deep-planting tr e a tm e n ts to p r e v e n t h e r b i c i d e because these two c h e m i c a l s a r e m o re w a t e r s o l u b l e t h a n s i m a z i n e , an d t h e y a l s o lity of sim azine is are f o li a r 5 ppm ( 2 ) , d i u r o n a n d 75 ppm f o r lin u ro n absorbed. contained (1 ). The p l a n t i n g s l i t may s h r i n k a g e from t h e s o i l t e x t u r e o f t h e Ap h o r i z o n 21 p e r c e n t c l a y , shrinkage p r o p e r tie s W ater s o l u b i ­ c o m p a r e d w i t h 42 ppm f o r h a v e opened s l i g h t l y b e c a u se of s o i l ev ap o tran sp iratio n ; i n j u r y may b e (12). which i n c r e a s e s t h e s o i l D u r i n g May, h e a v y r a i n s h a v e c a r r i e d m o re o f t h e m o re s o l u b l e h e r b i c i d e s , linuron, sim azine. The o t h e r e x p l a n a t i o n f o r t h e i n c r e a s e d dam ag e i n t h e d i u r o n and l i n u r o n d e e p - p l a n t e d read ily urea h e r b ic id e s , t r e a t m e n t s was t h a t s u b ­ in c o n t r a s t to s im a z in e , a b s o r b e d by t h e f o l i a g e the h e rb ic id e leav es d i u r o n an d down i n t o t h e s l i t c o m p a r e d w i t h t h e h i g h l y in so lu b le stitu ted could (1, t r e a t m e n t , a few t r e e s 5, 7). tim e of i n e a c h p l o t h ad new j u s t b r e a k i n g t h r o u g h t h e bud s c a l e s . made t o c o v e r At t h e a r e m ore No a t t e m p t was t h e s e e d l i n g s when e a c h p l o t was s p r a y e d b e c a u s e t h e s p r a y i n g p r o c e d u r e was t o s i m u l a t e a c t u a l a p p lic a tio n co n d itio n s. These e a r l y leafin g seed lin g s fie ld 16 suffered fo liag e h erb icid e to k i l l i n j u r y an d may h a v e a b s o r b e d s u f f i c i e n t th e m . The e f f e c t i v e n e s s o f p l a s t i c m u l c h i n c o n t r o l l i n g chem ical i n j u r y was i n t e r m e d i a t e when c o m p a r e d t o t h e two sim azine treatm en ts. had p o o r e r s u r v i v a l m ent, The p l a s t i c m u l c h (sim azine) than the d e e p - p la n tin g treatm ent (sim azine) tre at­ b u t b e t t e r s u r v i v a l than the r e g u l a r - p l a n t i n g (sim azine) treatm en t. zine in ju ry , A lthough th e p l a s t i c i t did not p re v e n t t h e p l a s t i c was t h a t it. it co llected s p r a y and t h e n f u n n e l e d lessened The m a i n p r o b l e m w i t h an d p o o l e d t h e h e r b i c i d e some o f t h e c h e m i c a l p l a s t i c a t th e h o le around th e ro o t c o l l a r . p l a s t i c m ulch around i n d i v i d u a l sim a­ through the The u s e o f stem s to p r e v e n t h e r b i c i d e dam a g e s h o u l d b e r e e v a l u a t e d b e c a u s e o f i t s c o s t i n l a b o r and m a t e r i a l s a s w e l l a s i t s u n c e r t a i n e f f e c t i v e n e s s . The good t o e x c e l l e n t s im a z i n e compared to (82-89%) weed c o n t r o l the m oderate (56-62%) weed c o n t r o l e x h i b i t e d b y d i u r o n and l i n u r o n was d u e l a r g e l y ch em istry of the h e r b ic id e s . (2.0%) and t h e slig h tly The l o w s o i l a c i d i c pH (6.7) to th e organic m atter o f t h e Ap h o r i z o n were f a v o r a b l e f o r c h e m ic a l a c t i v i t y o f a l l herb icid es. p r o d u c e d by However, u n d er t h e s e c o n d i t i o n s three sim azine gave b e t t e r weed c o n t r o l p a r t l y b e c a u s e s i m a z i n e - t o l e r a n t , l a t e season g r a s s e s d id n o t in v ad e th e sim azine p l o t s summer. S i m a z i n e was p r o b a b l y m ore p e r s i s t e n t b e c a u s e i t was m o re i n s o l u b l e and l e s s an d linuron. v o latile in late in th e s o i l than d iu ro n 17 A c h i e v i n g e x c e l l e n t weed c o n t r o l m oderate to high a p p l i c a t i o n (75-100%) by u s i n g r a t e s o f c h e m ic a ls such as s i m a z i n e may n o t b e a d v i s a b l e b e c a u s e o f t h e i n c r e a s e d r i s k of m o rta lity . T h i s was t h e c a s e w i t h t h e s i m a z i n e p l o t s , w h i c h a v e r a g e d 86 p e r c e n t weed c o n t r o l c o m p a r e d t o 60 p e r c e n t f o r t h e d i u r o n and l i n u r o n p l o t s . b e t t e r weed c o n t r o l , poorer s u r v iv a l diuron sim azine D esp ite having ( r e g u l a r - p l a n t i n g ) p l o t s h ad an d g r o w t h a f t e r t h r e e y e a r s t h a n d i d (reg u lar-p lan tin g ) the p lo ts. The a b s e n c e o f s i g n i f i c a n t c o r r e l a t i o n s b e t w e e n f i r s t y e a r weed c o n t r o l an d t h e t h r e e y e a r s o f g r o w t h d a t a suggested th a t the i n i t i a l weed c o n t r o l , 35 p e r c e n t i n some p l o t s , grow th i n h i b i t i o n was s u f f i c i e n t w h i c h was a s l o w a s to av o id s e r io u s f r o m weed c o m p e t i t i o n . T his la c k of c o r r e l a t i o n b e t w e e n w e e d s a n d g r o w t h a g r e e d w i t h B e n s o n and E inspahr (3) who f o u n d t h a t when g r e a t e r o f t h e v e g e t a t i v e c o v e r was c o n t r o l l e d , t h a n 50 p e r c e n t low s u r v i v a l or r e d u c e d t r e e g ro w th r e s u l t e d , p r e s u m a b l y from c h e m i c a l to x icity . They c o n c l u d e d t h a t c o m p l e t e c o n t r o l n o t n e c e s s a r i l y a good c r i t e r i o n h erbicides. These r e s u l t s to judge th e u s e f u l n e s s of im ply t h a t p r e v e n t i o n o f h e rb ic id e in ju ry w hile s t i l l a c h i e v i n g g o o d s u r v i v a l and grow th i s a b e t t e r s t r a t e g y th a n t r y i n g weeds. to c o n tro l T h e r e f o r e , on an a v e r a g e o r b e t t e r site, s u c c e s s f u l l y e s t a b l i s h e d e v e n i f weed c o n t r o l or less fo r the f i r s t of weeds i s grow ing s e a s o n . all a s p e n can be i s 50 p e r c e n t 18 LITERATURE CITED 1 . A n d e r s o n , W.P. Weed S c i e n c e : Co. New Y o r k . 1 9 7 7 . 598 p p . 2. P r i n c i p l e s . W es t P u b l i s h i n g A u d u s , L . J . The P h y s i o l o g y an d B i o c h e m i s t r y A c a d e m i c P r e s s . New Y o r k . 1 9 6 4 . 555 p p . of H erbicides. 3 . B e n s o n , M.K.; E i n s p a h r , D.W. C h e m i c a l c o n t r o l o f v e g e t a t i v e c o m p e t i t i o n i n a s p e n p l a n t i n g s . T r e e P l a n t e r s ' N o t e s N o . 67. 1964. 4 . B e n s o n , M.K. B r e e d i n g and e s t a b l i s h m e n t — an d p r o m i s i n g h y b r i d s . I N / A s p e n Symposium P r o c . USDA F o r . S e r v . Gen. T e c h . R e p . NC-1. p p . 8 8 - 9 6 . 1 9 7 2 . 5. D a n f i e l d , W.; M a r t i s h u s , J . ; H a n s e n , E. A p p l i c a t i o n d a t e a f f e c t s h e r b i c i d e t o l e r a n c e o f h y b r i d p o p l a r s . USDA F o r . S e r v . R es. N ote NC-301. 1983. 6 . D i c k m a n n , D . I . ; H e i l i g m a n n , R . ; G o t t s c h a l k , K. H e r b i c i d e s a id e s ta b lis h m e n t of u n ro o te d p o p la r c u t t i n g s . Tree P l a n t e r s ' N o t e s 28 (3&4) : 1 0 - 1 3 . 1 9 7 8 . 7. G i l c h r i s t , A.N. More h e r b i c i d e s f o r s o i l t r e e n u r s e r i e s . I N / P r o c . 3 4 t h N . Z . Weed C onf.:1 0 4 - 1 0 6 . 1981. co nservation and P e s t C o n t r o l 8. N e t z e r , D . A . ; N o s t e , N.V. H e r b i c i d e t r i a l s i n i n t e n s i v e l y c u l t u r e d Populus p l a n t a t i o n s in n o r th e r n W isc o n sin . USDA F o r . S e r v . R e s . N o t e N C -2 3 5 . 1 9 7 8 . 9. R o a d h o u s e , F . E . B . ; B i r k , L . A . P e n e t r a t i o n o f and p e r s i s t e n c e in s o i l of th e h e r b i c i d e 2 - c h l o r o - 4 , 6 - b is ( e t h y l a m i n o ) - s - t r i a z i n e ( s i m a z i n e ) . Can. j . P l a n t S c i . 4 1 :2 5 2 -2 6 0 . 1961. 1 0 . S t e e l , R . G . D . ; T o r r i e , J . H . P r i n c i p l e s an d P r o c e d u r e s o f S t a t i s t i c s . M c G r a w - H i l l Book C o. 1 9 6 0 . 481 p p . 1 1 . Von A l t h e n , F.W. E f f e c t s o f s i t e p r e p a r a t i o n an d p o s t ­ p l a n t i n g weed c o n t r o l on t h e s u r v i v a l an d h e i g h t g r o w t h o f p l a n t e d hardwood s e e d l i n g s . Can. F o r . S e r v . , S a u l t S t e . M a r i e , O n t . , Rep . O - X - 2 4 8 . 15 p p . 1 9 7 6 . 1 2 . ______ . S i t e p r e p a r a t i o n p r e v e n t s r e - o p e n i n g o f p l a n t i n g s l i t s in h e a v y - t e x t u r e d s o i l s . F o r. C hron. 5 3 :1 6 6 -1 6 7 . 1977. 1 3 . ______ . P r e l i m i n a r y g u i d e t o s i t e p r e p a r a t i o n an d weed c o n t r o l in hardwood p l a n t a t i o n s in s o u t h e r n O n t a r i o . Can. F o r . S e r v . , S a u l t S t e . M a r ie , O n t. R e p o r t O-X-288. 22 p p . 1 9 7 9 . 18 19 14. . P l a n t i n g s t u d i e s w i t h h y b r i d p o p l a r s an d c o t t o n w o o d i n s o u t h w e s t e r n O n t a r i o . Can. F o r . S e r v . , S a u l t S t e . M a r i e , O n t . R e p . O - X - 3 3 2 . 17 p p . 1 9 8 1 . 1 5 . W e l d o n , L . W . ; Timmons, F . L . P e n e t r a t i o n and p e r s i s t e n c e o f d i u r o n i n s o i l . Weeds 9 : 1 9 5 - 2 0 3 . 1 9 6 1 . CHAPTER 2 PROGENY TESTING OF NATIVE ASPENS AND THEIR HYBRIDS FOR BIOMASS PRODUCTION IN MICHIGAN ( P r e s e n t e d a t t h e 1984 NEFTIC M e e t i n g i n M o r g a n t o w n , WV.) ABSTRACT An a s p e n p r o g e n y t e s t c o n s i s t i n g trem bling aspen g ran d id en tata) , (P o p u l u s o f 206 f a m i l i e s o f tre m u lo id e s ) , b ig to o th aspen an d t h e i r h y b rid s (P. Xs m i t h i i (P. a n d P. Xr o u l e a u i a n a ) was p l a n t e d on f i v e M i c h i g a n s i t e s and ev aluated after tw o g r o w i n g s e a s o n s . Growth p e r f o r m a n c e o f t r e m b l i n g a s p e n f a m i l i e s when c o m p a r e d w i t h a l l was a b o v e a v e r a g e a n d i n c r e a s e d w i t h t h e p lan tatio n site . aspen taxa l a t i t u d e of the B ac k cro sses of tre m b lin g aspen m ales to w hite p o p l a r - b i g t o o t h aspen (£. X r o u l e a u i a n a ) f e m a l e s produced th e f a s t e s t grow ing f a m i l i e s a t a l l P eninsula p la n ta tio n s . Most h y b r i d a s p e n Lower (P. X s m i t h i i ) f a m i l i e s had g ro w th r a t e s b e lo w t h e p l a n t a t i o n means. B i g t o o t h a s p e n f a m i l i e s had p o o r s u r v i v a l p lan tatio n s. A n a l y s e s o f two n e s t e d m a t i n g d e s i g n s showed t h a t g e n e r a l com bining a b i l i t y (ad d itiv e g en etic f o r h e i g h t an d d i a m e t e r g r o w t h was p r e s e n t po p ulation. an d g r o w t h a t a l l variance) in th e aspen G e n o t y p e x e n v i r o n m e n t i n t e r a c t i o n was s m a l l a t th e fam ily l e v e l . 20 21 INTRODUCTION The a s p e n s a r e fast-grow ing trees s t u d i e d by numerous p o p l a r b r e e d e r s , little t h a t h av e been but u n fo rtu n ately p r o g r e s s h a s b e e n made i n i m p r o v i n g t h e g e n e t i c b a s e of th e s p e c ie s . L a rg e am ounts o f g e n e t i c trem b ling (P o p u l u s t r e m u l o i d e s ) and b i g t o o t h a s p e n aspen v ariatio n (P o p u l u s g r a n d i d e n t a t a ) h a v e b e e n r e p o r t e d E i n s p a h r and B e n s o n 1 9 6 7 , B arn es 1969). in ( P a u le y 1949, This g e n e tic v a r i a t i o n p r o v i d e s an a m p l e g e r m p l a s m b a s e f o r a t r e e im provem ent program . F u rth erm o re, b e t w e e n t h e two s p e c i e s p erm its the b reed er d esired tra its. (P a u le y 1956, H e n r y an d B a r n e s to c r e a t e a d d i t i o n a l v ariatio n "capture" the g e n e tic in a s p e n i s how t o q u a n t i f y an d v ariatio n has been d i f f i c u l t to e s t a b l i s h s p e c i e s an d t o e l i m i n a t e b i a s found in th e species. te s t p lan tatio n s fo r the com m unication). asp en p ro g en y t e s t were to : (1) q u a n t i f y t h e g e n e t i c v ariatio n p o p u latio n s (2) c r e a t e a d d i t i o n a l in M ichigan, in th e n a t i v e aspen g en etic v a r i a t i o n by h y b r i d i z i n g t h e two n a t i v e a s p e n s p e c i e s , (3) aspen f a m ilie s fast-grow ing biom ass p l a n t a t i o n s , d ifferen t site s environm ent an d in o rd e r in tera ctio n s. (4) e s t a b l i s h to It from g e n o t y p e x e n v i r o n m e n t ( E i n s p a h r a n d Mohn, p e r s o n a l The o b j e c t i v e s o f t h i s id en tify 1977) The p r o b l e m t h a t g e n e t i c i s t s h a v e e n c o u n t e r e d when b r e e d i n g in tera ctio n s the ease of h y b r id iz a tio n for sh o rt-ro tatio n a p r o g e n y t e s t on i n v e s t i g a t e genotype x 22 MATERIALS AND METHODS P ro g en y P r o d u c t i o n and M ating D esig n S e e d and c a t k i n - b e a r i n g b r a n c h e s o f b i g t o o t h and t r e m b lin g aspen were c o l l e c t e d f r o m 43 c o u n t i e s in b oth p e n i n s u l a s o f M i c h i g a n d u r i n g M ar ch an d A p r i l o f 1979 and 1 980. S im ilar m ateria l big to o th aspen f r o m two p u t a t i v e w h i t e p o p l a r - (P. X r o u l e a u i a n a ) h y b r i d s lo cated in th e s o u t h e r n Lower P e n i n s u l a o f M i c h i g a n was a l s o c o l l e c t e d . C o n t r o l l e d - p o l 1 i n a t i o n s w e r e made u s i n g t h e c u t - b r a n c h technique (E inspahr p o llin atio n s and Benson 1964). from t h e r e p r e s e n t e d 48 h a l f - s i b an d 66 f u l l - s i b fa m ilie s of b ig to o th fu ll-sib P rogenies and t r e m b l i n g a s p e n . f a m ili e s of h ybrid g r a n d i d e n t a t a X P. aspen In a d d i t i o n , 72 (P. X s m i t h i i = P. t r e m u l o i d e s ) a n d 20 backcrosses of b i g t o o t h an d t r e m b l i n g a s p e n t o t h e p u t a t i v e w h i t e p o p l a r h y b rid , P. X r o u l e a u i a n a (P. a l b a x P. g r a n d i d e n t a t a ) , w e r e produced. The m a t i n g d e s i g n u s e d d esig n i n t h e p r o g e n y t e s t was a n e s t e d ( N o r t h C a r o l i n a D e s i g n 1) w h i c h l a t e r was r e d u c e d s iz e because of the s u f f i c i e n t seed. fa ilu re o f some c r o s s e s t o p r o d u c e A fte r adjustm ent fo r m issing n e s t e d d e s i g n s were c o n s t r u c t e d f a m i l i e s t h a t were w e l l first in th e f i e l d p o pulation two tests. The ( f o u r e a c h o f b i g t o o t h an d t r e m b l i n g aspen) which were each c r o s s e d T h eo retically , fam ilies, f r o m 46 o f t h e 158 f u l l - s i b represented d e s i g n had e i g h t m a l e s each s p e c ie s . in t o two f e m a l e s o f random s a m p l i n g o f t h e in th e n e s te d d e s ig n would d i c t a t e th at fem ales 23 be c r o s s e d o n l y o n c e , b u t in t h i s t e s t fo u r f e m a le s w ere used tw ice because o f s i g n i f i c a n t m o r t a l i t y i n some fam ilies. (8 m a l e s an d 28 fem ales) The d e s i g n c o m p r i s e d 32 f a m i l i e s an d was r e p l i c a t e d s ix tim es in one p l a n t a t i o n . The s e c o n d d e s i g n t e s t e d s e v e n t r e m b l i n g a s p e n m a l e s w h i c h w e r e e a c h c r o s s e d w i t h two d i f f e r e n t t r e m b l i n g a s p e n fem ales. T h e r e w e r e 14 f a m i l i e s (7 m a l e s a n d 14 f e m a l e s ) t h i s d e s i g n , an d t h e y w e r e r e p l i c a t e d in 16 t i m e s a c r o s s t h r e e p lan tatio n s. S e e d was sown i n t h e n u r s e r y on May 2 6 , cu ltu ra l 1 9 8 1 , and p r o c e d u r e s s i m i l a r t o t h o s e o f B e n s o n and Dubey (1972) w e r e u s e d t o g r o w t h e c o n t r o l l e d w ith O rthene. seed lin g s. I n s e c t s were The mean h e i g h t f o r e a c h f a m i l y in t h e n u r s e r y was r e c o r d e d b e f o r e t h e s e e d l i n g s w e r e l i f t e d t h e f o l l o w i n g M a rc h and p l a c e d p lan tin g season in c o l d s t o r a g e u n t i l the started . P l a n t a t i o n S i t e s and Aspen E s t a b l i s h m e n t P r o c e d u r e s The f i v e p l a n t a t i o n abandoned a g r i c u l t u r a l s i t e s chosen fo r t h i s fie ld s. Three p l a n t a t i o n s a r e in th e Lower P e n i n s u l a o f M i c h i g a n an d two a r e P eninsula. S tate L at. i n t h e Upper The Lower P e n i n s u l a p l a n t a t i o n s a r e a t M i c h i g a n U n iv e rs ity 's 42.0°N, s tu d y were Long. (MSU) R u s s E x p e r i m e n t a l 86.0°W) , Forest MSU W a t e r Q u a l i t y ( C a s s C o., R e s e a r c h Area ( I n g h a m C o . , L a t . 4 2 . 7 ° N , L o n g . 84.5°W ) , a n d M i c h i g a n C o n s o l i d a t e d Gas C o m p a n y 's g a s s t o r a g e f i e l d s n e a r t h e town o f S i x L a k e s ( M e c o s t a C o . , L a t . 4 3 . 5 ° N , L o n g . 8 5 . 2 ° W). so il t e x t u r e s o f t h e Russ F o r e s t , W ater Q u a l i t y , an d S i x The 24 Lakes s i t e s a r e a sandy loam , a f i n e loam , r e s p e c t i v e l y . s a n d y l o a m , an d a s a n d y G r a s s e s and p e r e n n i a l w e e d s w e r e t h e dom inant v e g e t a t i o n on t h e s e s i t e s . The two U p p e r P e n i n s u l a p l a n t a t i o n s a r e a t t h e M i c h i g a n S tate a g r ic u ltu r a l L at. 4 6 . 3 °N , L ong. fie ld statio n 86.9°W) n e a r C h a t h a m ( A l g e r Co., an d on N e e b i s h C o., L a t . 4 6 .3 °N , Long. 84.2°W ). Island ( C hippew a Th e C h a t h a m p l a n t a t i o n is on a f o r m e r a l f a l f a f i e l d w h i c h h a s a f i n e s a n d y l o a m so il tex tu re. The N e e b i s h I s l a n d p l a n t a t i o n was a c l o v e r an d t i m o t h y f i e l d w i t h a h e a v y c l a y s o i l w h i c h was m o t t l e d a t a d e p t h o f 20 cm. The s o i l s a t a l l p l a n t a t i o n s e x c e p t N eeb ish I s l a n d were w e l l - d r a i n e d . S ite p rep aratio n fo r each of th e f i v e p l a n t a t i o n s c o n s i s t e d o f mowing t h e e x i s t i n g mower i n A u g u s t , v e g e ta tio n w ith a r o ta r y 1981 an d s p r a y i n g s e v e n l i t e r s / h a g ly p h o s a te in one-m eter-w ide s t r i p s later. I n A p r i l an d May o f 1 9 8 2 , a t th e s e f i v e M ichigan l o c a t i o n s . m achine-planted t h r e e to f o u r weeks th e s e e d l i n g s were p l a n t e d The s e e d l i n g s w e r e i n t w o - t r e e p l o t s w i t h a s p a c i n g o f 1.8 m e te r s betw een t r e e s w i t h i n rows, rows. of a n d 2.4 m e t e r s b e t w e e n The e x p e r i m e n t a l d e s i g n was a r a n d o m i z e d b l o c k w i t h s ix r e p l i c a t i o n s a t each p l a n t a t io n . p lan tin g , 2.8 k g / h a a . i . Follow ing sp rin g o f s i m a z i n e was a p p l i e d over the t o p s o f t h e s e e d l i n g s and o n t o t h e g l y p h o s a t e - s p r a y e d strip s. The p l a n t i n g strip s i n t h e W a t e r Q u a l i t y an d S i x Lakes p l a n t a t i o n s were s p o t - s p r a y e d once w ith g l y p h o s a t e J u l y , 1982 t o c o n t r o l invading g ra s s e s . in 25 D ata A n aly ses H e i g h t , b a s a l d i a m e t e r , and s u r v i v a l all of th e f a m il i e s th e p l a n t a t i o n s e x c e p t N eeb ish I s l a n d were t a l l i e d 1982 an d 1 9 8 3 . in in The d i a m e t e r s w e r e s q u a r e d an d t h e n m u l t i p l i e d b y t h e h e i g h t s t o g i v e an i n d e x o f b i o m a s s pro d u ctio n (=biomass p r o d u c t i o n index). A nalyses of v a r i a n c e and c o r r e l a t i o n s w ere c a l c u l a t e d b a s a l d ia m e te r , biom ass p r o d u c tio n m easurem ents. for a l l h eig h t, i n d e x , an d o t h e r g r o w t h F a m ily p e rfo rm a n c e s in a l l a n a l y s e s were b a s e d on t h e p l o t m e a n o f e a c h f a m i l y w h i c h w a s e x p r e s s e d i n p e rc e n t of the b lo ck (rep licate) mean. F a m i l y an d s p e c i e s p e r f o r m a n c e s w i t h i n , an d b e t w e e n g e o g r a p h i c a l M ichigan were e v a l u a t e d f o r t r e n d s and g e n o t y p e x environm ent i n t e r a c t i o n s . and d i a m e t e r w e r e d e r i v e d first nested d esig n . an d e v a l u a t e d re g io n s of H e r ita b ility estim ates for height from a n a l y s e s o f v a r i a n c e o f t h e M a l e an d f e m a l e e f f e c t s w e r e t e s t e d fo r th e p a r e n ts used in b o th n e s te d d e s ig n s . A ge-age c o r r e l a t i o n s were c a l c u l a t e d fo r the r e l a t i o n s h i p of f i r s t - y e a r n u rse ry h e ig h t to th e tw o -y e a r-o ld p l a n t a t i o n height data. RESULTS AND DISCUSSION F a m i l y P e r f o r m a n c e Among P l a n t a t i o n s Two-year s u r v i v a l (taxon) is listed plan tatio n s. of th e f a m i l i e s w ith in each c ro ss i n T a b l e 2.1 f o r the three best The R u s s F o r e s t an d N e e b i s h I s l a n d p l a n t i n g s w e r e n o t l i s t e d b e c a u s e m o r t a l i t y was g r e a t e r t o h e r b i c i d e dam age a n d d r o u g h t . S u rv iv al t h a n 50% d u e in c r e a s e d w ith 26 decreasing l a t i t u d e of the p la n ta tio n s . S u r v iv a l a t the C h a t h a m p l a n t a t i o n was s e v e n and 11 p e r c e n t l e s s t h a n t h a t a t S i x L a k e s and W a t e r Q u a l i t y (East L ansing), resp ectiv ely . The f r e e z e - f r e e p e r i o d o r g r o w i n g s e a s o n a t C h a t h a m i s 100 d a y s c o m p a r e d t o 126 d a y s a t S i x L a k e s an d 151 d a y s a t E a s t Lansing ( M ic h . D ept. A gric. 1971). The s h o r t e r s e a s o n an d o t h e r e n v i r o n m e n t a l s t r e s s e s reduced the s u r v i v a l o f P. X s m i t h i i sig n ifican tly f a m i l i e s a t Chatham. S u r v i v a l o f t h e two n a t i v e a s p e n s v a r i e d th ree growing little ac ro ss the p lan tatio n s. T a b l e 2 .1. Two-year s u r v i v a l in p e r c e n t f o r as p e n t a x a a t th ree p la n ta tio n s . P lan tatio n S ite Taxa ( F e m a l e X M ale) Chatham1 S ix Lakes W ater Q u a l i t y Populus tre m u lo id e s X P. t r e m u l o i d e s 92 90 97 P. 68 89 91 (P. X r o u l e a u i a n a ) X P. t r e m u l o i d e s 84 88 99 P. g r a n d i d e n t a t a X P. g r a n d i d e n t a t a 72 73 75 P. g r a n d i d e n t a t a X P. t r e m u l o i d e s 72 86 87 (P. X r o u l e a u i a n a ) X P. g r a n d i d e n t a t a 64 63 79 A l l Ta xa Combined 79 86 90 trem uloid es X P. g r a n d i d e n t a t a ^■Replicates 4 -6 were n o t included because of h e r b ic id e o v erd o se. 27 Rapid j u v e n i l e grow th i s p o s i t i v e l y c o r r e l a t e d w ith aspen s u r v i v a l 1967, ( P a u l e y e t al_. 1 9 6 3 a r H a t t e m e r a n d S e i t z M e l c h i o r and S e i t z 1 9 6 6 , grow ing f a m i l i e s in t h i s M ohrdiek 1979a). t e s t a l s o had t h e The f a s t e s t low est m o r ta lity . B i g t o o t h a s p e n an d t h e h y b r i d s g r e w p o o r l y on t h e C h a t h a m s i t e an d c o n s e q u e n t l y , s u ffe re d s i g n i f i c a n t l y higher m o rtality than th e tre m b lin g aspen f a m i l i e s . in itia lly s l o w - g r o w i n g s p e c i e s an d h y b r i d s s h o u l d n o t b e p lan ted in a r e a s w ith s e v e r e c l i m a t i c c o n d i t i o n s b e c a u s e early m o rtality is these These lik ely to be h ig h . However, if some o f f a m i l i e s become f a s t g r o w e r s once t h e y a r e esta b lish ed , p lan tin g t h e e a r l y m o r t a l i t y c a n be c o m p e n s a te d f o r by at higher d e n s itie s . The a n a l y s e s o f v a r i a n c e sh ow ed t h a t d i f f e r e n c e s i n height, basal sig n ific a n t d iam eter, (P<.05) w ith in -tax a a t a l l for an d b i o m a s s p r o d u c t i o n in d iv id u al p lan tatio n s h i g h e s t f a m i l y means f o r best p lan tatio n resp ectiv ely f a m i l i e s an d f a m i l i e s - i n y e a r s 1982 a n d 1 9 8 3 . The t w o - y e a r h e i g h t and d i a m e t e r a t t h e (W ater Q u a l i t y ) (Table index were 2.2). were 2.8 m e t e r s a n d 3.3 cm., The h e i g h t an d d i a m e t e r o f the f i v e t o p f a m i l i e s when a v e r a g e d o v e r f o u r p l a n t a t i o n s w e r e 1.6 m e t e r s an d 1. 9 cm., resp ectiv ely . f a m i l i e s was c o m p a r a b l e o r g r e a t e r prom ising fa m ilie s of trem bling h ybrid aspen (P auley e t a ^ . ( B e n s o n and E i n s p a h r (Johnson 1942), 1967), than t h a t re p o rte d aspen 1963c), E a r l y grow th of (P auley e t a l . trip lo id these for 1963b), h y b rid aspen w hite p o p la r - b ig to o th h y b rid s an d w h i t e p o p l a r - a s p e n trih y b rid s (Maynard 1977). 28 T a b l e 2.2. Tw o-year grow th p e rfo rm a n c e o f th e b e s t f a m il y an d i n d i v i d u a l o f e a c h a s p e n t a x o n a t t h e W a t e r Q u ality p la n ta tio n . B e s t Fam ily A s p en T a x o n B est In d iv id u al (Mean) 1983 H t 1 (cm) 1983 Diam2 (cm) 1983 Ht (cm) Populus trem u lo id es 273 3.1 395 4.6 P. g r a n d i d e n t a t a 232 2.6 345 3.8 P. X s m ith ii 275 3.3 435 5.6 (P. X r o u le a u ia n a ) X P. t r e m u l o i d e s 254 2.9 360 4.6 ^ H e i g h t s w e r e m e a s u r e d t o t h e n e a r e s t 5 cm. 2 D i a m e t e r s w e r e m e a s u r e d a t 5 cm a b o v e t h e s o i l 1983 Diam (cm) surface. To e v a l u a t e t h e g r o w t h p o t e n t i a l o f t h e s e f a m i l i e s , biom ass p r o d u c tio n h e i g h t , was u s e d . w ithin index, b a s a l d iam eter squared tim es C o r r e la tio n s of h e ig h t to b a s a l d iam eter p lan tatio n s ranged f r o m .73 t o .89 an d w e r e s i g n i f i c a n t a t t h e one p e r c e n t p r o b a b i l i t y (1 9 7 9 a) the sum m arized lev el. M ohrdiek t h e f i n d i n g s o f many P o p u l u s g e n e t i c s t u d i e s an d c o n c l u d e d t h a t h e i g h t i s h i g h l y c o r r e l a t e d w i t h diam eter fo r a l l p o p lars. h e i g h t an d d i a m e t e r p ro d u ctio n i s high S in c e th e c o r r e l a t i o n betw een in p o p l a r s , th e biom ass i n d e x was c o n s i d e r e d a v a l i d m e a s u r e o f b i o m a s s p ro d u ctiv ity . The b i o m a s s p r o d u c t i o n p lan tatio n s is index of each tax o n a t shown i n T a b l e 2. 3. four The nu m b er o f f a m i l i e s o f e a c h t a x o n t h a t w e r e among t h e t o p 25 f a m i l i e s in biom ass 29 p ro d u ctio n 2.4. index a t each p l a n t a t i o n The nu mber of trem b lin g in creased w ith in c re a sin g a r e summ arized aspen f a m il i e s latitu d e. i n t h e t o p 25 l a t i t u d e of the p l a n t a t i o n w h i l e t h e number o f h y b r i d and t r i h y b r i d w ith d e c re a sin g T rem bling aspen f a m i l i e s t r e m b l i n g a s p e n and t h e t r i h y b r i d w e r e b e s t biom ass p r o d u c t io n index o v e r a l l a trih y b rid , biom ass p r o d u c tio n T able 2.3. site, fa m ilie s increased c o m p r i s e d 19 o f t h e 25 b e s t f a m i l i e s o v e r a l l . b e st fam ily , in T a b le F a m ilie s of in term s of four p la n ta tio n s . The a v e r a g e d 28% a b o v e t h e mean index f o r a l l f a m i l i e s a t a g e tw o. Biomass p r o d u c t i o n in d e x ( d ia m e te r ^ X h e i g h t ) i n % o f p l a n t a t i o n mean f o r f i v e a s p e n t a x a i n fo u r M ichigan p l a n t a t i o n s . Taxon P lan tatio n L atitu d e AGxT1 ( F e m a l e X Male) TG,GT3 TT2 ___ Chatham Six Lakes W ater Q u a l i t y Russ F o r e s t 4 6 . 3° N. 4 3 . 5° N. 4 2 . 7°N . 4 2 . 0°N. Combined 1 (Populus a lb a X £ . AGXG4 GG5 &______ 114 125 123 160 133 116 116 108 74 81 94 76 66 86 74 86 46 51 61 76 122 120 84 77 56 g r a n d i d e n t a t a ) X P. trem uloides 2P . t r e m u l o i d e s X P. trem uloides 3P . t r e m u l o i d e s X P. g r a n d i d e n t a t a and t h e r e c i p r o c a l c r o s s 4 (P. a l b a X P. g r a n d i d e n t a t a ) X P. g r a n d i d e n t a t a 5P. g r a n d i d e n t a t a X P. g r a n d i d e n t a t a 30 T a b l e 2 .4. Number o f f a m i l i e s o f e a c h t a x o n t h a t c o m p r i s e t h e 25 f a m i l i e s w i t h t h e h i g h e s t b i o m a s s p r o d u c tio n in d ic e s a t each p l a n t a t i o n . P lan tatio n S ite W ater Russ Six C h a th a m L a k e s Q u a l i t y F o r e s t Combined Taxon ( F e m a l e X Male ) Populus tre m u lo id e s X P. t r e m u l o i d e s 20 16 12 11 19 (P. x r o u l e a u i a n a ) X P. tr e m u l o i d e s 2 4 4 6 4 P. X s m ith ii (plus r e c ip r o c a l) 2 5 7 6 2 - - 1 1 - 1 — 1 1 — (P. X r o u le a u ia n a ) X P. g r a n d i d e n t a t a P. g r a n d i d e n t a t a X P. g r a n d i d e n t a t a Fam ily x S i t e I n t e r a c t i o n C o r r e l a t i o n s betw een taxon p erfo rm an ce pro d u ctio n index) a t each p l a n t a t i o n w ith i t s perform ance over a l l p la n ta tio n s are lis te d The p e r f o r m a n c e o f i n d i v i d u a l (biom ass resp ectiv e i n T a b l e 2.5. f a m il i e s a t each p l a n t a t i o n s i t e was s i g n i f i c a n t l y c o r r e l a t e d w i t h t h e i r a v e r a g e perform ance over the four site s (r= .68 to .77), although b i g t o o t h a s p e n f a m i l i e s a t S i x L a k e s w e r e an e x c e p t i o n . c o r r e la tio n data im p lie d t h a t a lth o u g h genotype x s i t e in tera ctio n s were p r e s e n t , t h e y were n o t s t r o n g fam ily l e v e l under th e p a r t i c u l a r c o n d itio n s of t h i s a t the T h e s e f i n d i n g s a g r e e w i t h t h o s e o f H a t t e m e r and S e i t z who r e p o r t e d The th a t fam ily x s i t e in tera ctio n s test. (1967) for h eig h t data 31 o f h y b r i d a s p e n i n Germany w e r e n o n - s i g n i f i c a n t . resu lts s u g g e s t t h a t m o s t a s p e n f a m i l i e s h a d good correspondence i n p e r f o r m a n c e a t two y e a r s a c r o s s t h e environm ents t e s te d . T herefore, e x p r e s s e d grow th s u p e r i o r i t y T able The 2.5. th e fast-g ro w in g genotypes in d i f f e r e n t environm ents. C o r r e l a t i o n s o f ta x o n p e rfo rm a n c e (biom ass p r o d u c t i o n i n d e x ) a t e a c h p l a n t a t i o n w i t h mean p erfo rm an ce of each taxon fo r a l l p l a n t a t i o n s . P la n ta tio n S ite^ Taxon ( F e m a l e X Male) Number o f F am ilies Six W ater Russ Chatham Lakes Q u a l i t y F o r e s t ------------------------r --------------- Populus tre m u lo id e s X P. tr e m u lo id e s 73 .63 .61 .62 .74 P. trem ulo ides X P. g r a n d i d e n t a t a 37 .73 .58 .86 .78 P. g r a n d id e n ta ta X P. g r a n d i d e n t a t a 34 .68 .7 0 .90 P. g r a n d i d e n t a t a X P. t r e m u l o i d e s 35 .31 ♦ .75 .58 .67 .77 .74 .68 .71 A l l Ta xa Com bine d 179 - .0 5 ns A l1 c o r r e l a t i o n c o e f f i c i e n t s w ithout a s te r i s k s s i g n i f i c a n t a t the 1 p e rc e n t l e v e l. ♦ S ig n ific a n t a t th e 5 p ercen t le v e l, ns N o n - s i g n i f i c a n t a t th e 5 p e r c e n t l e v e l . T r e m b l i n g a s p e n and t r i h y b r i d biom ass p r o d u c tio n are f a m i l i e s had s i m i l a r i n d i c e s an d e x h i b i t e d g r o w t h r a t e s e x c e e d e d t h e mean a t a l l p lan tatio n s. a s p e n f a m i l i e s were s u p e r i o r However, that trem bling in g ro w th and s u r v i v a l to a l l 32 o t h e r a s p e n t a x a a t C h a t h a m (Upper P e n i n s u l a ) , trih y b rid w hereas f a m i l i e s g r e w t h e b e s t a t t h e t h r e e Lower P eninsula p la n ta tio n s . T rem bling aspen f a m i l i e s d id w e ll t h e U pper P e n i n s u l a b e c a u s e t h e s p e c i e s north ern c lim a te s of trem bling than th e o th e r aspen f a m il i e s taxa tax a in c re a se d w ith in c r e a s in g i s m o re a d a p t e d t o tested . in r e l a t i o n latitu d e in Perform ance to th e o th e r aspen of the p l a n ta tio n site . The p e r f o r m a n c e o f t r e m b l i n g a s p e n f a m i l i e s f r o m s i t e to s i t e d i f f e r e d trih y b rid , f r o m t h o s e o f b i g t o o t h a s p e n and t h e P. X r o u l e a u i a n a X P. t r e m u l o i d e s . The P. X r o u le a u ia n a b a c k c r o s s e s were n o t w e l l a d a p te d to th e sh o rter g r o w i n g s e a s o n an d c o l d e r The P. a l b a l i n e a g e C entral t e m p e r a t u r e s a t C h a th a m . in t h i s c ro s s p ro b a b ly o r ig in a te d o r S o u t h e r n E u r o p e and was l e s s e c o l o g i c a l l y adaptable in t h e Upper P e n i n s u l a This h y b rid d id perform w e ll than th e n a t i v e asp en s. i n t h e Lower P e n i n s u l a p lan tatio n s, p o s s ib ly because of the m ild e r c lim a te . o th e r hyb rid t a x a p e r f o r m e d b e l o w t h e mean a t t h e f o u r site s. T h e s e h y b r i d s may b e l a t e sp ecific sin ce th e ir percent b e tte r than a t o r a r e more s i t e sites, b u t g r o w t h was 65 a t th e south ern m o st p l a n t a t i o n t h e n o r t h e r n m o s t one trem bling sta rte rs, A ll perform ance v a r ie d m arkedly w ith s i t e . B i g t o o t h a s p e n grew p o o r l y a t a l l site s, in ( C h a th a m ) . (Russ F o r e s t ) In g e n e r a l , a s p e n f a m i l i e s g r e w b e s t on n o r t h e r n M i c h i g a n and h y b r i d and b i g t o o t h a s p e n f a m i l i e s g r e w b e t t e r sou th ern M ichigan site s. on 33 The u n i d i r e c t i o n a l trem bling, b ig to o th , clin es in r e l a t i v e p erform ance of an d t r i h y b r i d a s p e n from n o r t h e r n to s o u t h e r n p l a n t a t i o n s were u n d o u b t e d l y i n f l u e n c e d by th e la titu d e and c l i m a t e o f t h e p l a n t i n g appropriate s p e c ie s or h ybrid c lim a tic region, for study, is chosen Once t h e for a s p e c ific f a m i l y s e l e c t i o n c a n t h e n b e b a s e d on t h e av erag e perform ance fo r a l l From t h i s site. p la n ta tio n s w ithin th a t region. t r e m b l i n g a s p e n f a m i l i e s w o u ld be s e l e c t e d t h e U p p e r P e n i n s u l a an d c o l d r e g i o n s o f t h e Lower P e n in s u la , w hereas t r i h y b r i d throughout th e o th e r f a m i l i e s w ould be p l a n t e d a r e a s o f t h e Lower P e n i n s u l a . G eographic S i g n i f i c a n c e of P a re n t P a u l e y e t al^. ( 1 9 63a) f o u n d t h a t P. t r e m u l a f a m i l i e s from C e n t r a l E u rope grew f a s t e r fam ilies th a n N o rth e rn European in W eston, M a s s a c h u s e t t s . In t h i s te st, b e s t f a m i l i e s o v e r a l l w e r e p r o d u c e d b y 35 p a r e n t s f e m a l e s an d 18 m a l e s ) counties. F am ilies t h e 20 (17 r e p r e s e n t i n g 26 w i d e l y d i s p e r s e d f r o m t h e 206 i n t h e p r o g e n y t e s t inclu d ed a tre m b lin g a s p e n p a r e n t f r o m n o r t h e r n Lower M ichigan 43.8°N) (above L at. g r e w two p e r c e n t larg er that than f a m i l i e s w i t h U p p e r P e n i n s u l a t r e m b l i n g a s p e n p a r e n t s , an d fiv e percent la rg e r M ichigan t h a n f a m i l i e s w i t h s o u t h e r n Lower (below L a t. 43.8°N) trem bling aspen p a re n ts . F a m i l i e s t h a t h ad b i g t o o t h a s p e n p a r e n t s M i c h i g a n g r e w two t o t e n p e r c e n t l a r g e r b ig to o th aspen p a re n ts Up per P e n i n s u l a . f r o m s o u t h e r n Lower than f a m i l i e s w ith f r o m n o r t h e r n Lower M i c h i g a n and t h e The b e s t h y b r i d fam ilies (£. X s m i t h i i ) 34 w ere p ro d u c e d from p a r e n t s o f b o t h s p e c i e s i n s o u t h e r n Lower M i c h i g a n . eig h t percent la rg e r t h a t were l o c a t e d T h e s e f a m i l i e s g r e w two t o than d id h y b rid s w ith p a r e n ts from n o r t h e r n Lower M i c h i g a n and t h e U pp er P e n i n s u l a . F i n d i n g an e x i s t i n g n atu ral aspen p o p u la tio n c l o n e s ) w ith s u p e r i o r grow th w ould i n c r e a s e the g ain th a t w ould be a c h i e v e d in t h e f i r s t b r e e d i n g c y c l e . clo n al n a t u r e o f asp en (Barnes 1966, (50-100 However, Kemperman 1976) the and i t s l a r g e g e n e t i c v a r i a b i l i t y w o u l d n e c e s s i t a t e a s a m p l e s i z e so l a r g e t h a t i t would be i m p r a c t i c a l study co n tain ed h a l f - s i b and f u l l - s i b c l o n e s r e p r e s e n t i n g 43 c o u n t i e s . (206) used w ith in , in th is to progeny t e s t . the p r o g e n y f r o m 125 The n u m b e r o f f a m i l i e s t e s t was i n a d e q u a t e t o e s t i m a t e an d b e t w e e n s t a n d v a r i a t i o n F u rth erm o re, fa ilu re the o f t h e two s p e c i e s . o f some 50 o t h e r c l o n e s t o p r o d u c e progeny reduced th e e f f i c a c y of th e m ating d e s ig n s g en etic T his to d e t e c t v ariatio n . Even th o u g h s u p e r i o r asp en s t a n d s w ere n o t id en tified , t h e g e n e r a l g e o g r a p h i c l o c a t i o n o f t h e p a r e n t s was i m p o r t a n t to the perform ance of the c r o s s e s . Okafo (1 976 ) found th at w e s t e r n U p p e r P e n i n s u l a s o u r c e s o f b i g t o o t h and t r e m b l i n g a s p e n grow f a s t e r M ichigan s o u r c e s . Pauley e t a l . under greenhouse c o n d itio n s than o th e r O ther aspen r e s e a r c h e r s 1963a, Jo h n ss o n 1976, h a v e found t h a t as p e n p a r e n t s (B arnes 1959, M e l c h i o r and S e i t z 1966) from s p e c i f i c g e o g r a p h i c r e g io n s produce the b e s t progeny. In t h i s stud y, the b e s t b i g t o o t h and t r e m b l i n g a s p e n p a r e n t s came f r o m n o r t h e r n an d 35 s o u t h e r n Lower M i c h i g a n , r e s p e c t i v e l y . aspen is a b o real sp ecies, Lower M i c h i g a n a r e s i m i l a r sp ecies. Since tre m b lin g t h e c l i m a t e an d s o i l s o f n o r t h e r n to th e n o rth e rn range of th e S o u t h e r n Lower M i c h i g a n , h o w e v e r , h a s s o i l s and c lim a te th a t are l e s s r e p r e s e n ta tiv e of the b o re a l h a b i t a t of trem b lin g aspen. G enerally , p o p u l u s p r o g e n i e s from n o r t h e r n l a t i t u d e s grow p o o r l y a t lo w e r l a t i t u d e s b e c a u s e t h e s h o r t e r p h o t o p e r i o d an d warm er t e m p e r a t u r e s a r e t h o u g h t to in d u ce grow th c e s s a t i o n ( P a u l e y an d P e r r y t r e n d was a p p a r e n t i n some f a m i l i e s , m easured p l a n t a t i o n consequently, This b u t was r e l a t i v e l y i n s i g n i f i c a n t due to th e l a r g e v a r i a t i o n each geographic p o p u la tio n . 1954). in p h en o lo g y w i t h i n However, o n l y one o f t h e fo u r s i t e s was i n t h e U p p e r P e n i n s u l a ; t h e two p e r c e n t l o w e r g r o w t h r a t e o f f a m i l i e s w i t h t r e m b l i n g a s p e n p a r e n t s f r o m t h e U pper P e n i n s u l a may p a rtia lly be a t t r i b u t e d to t h i s latitu d in al effect. I n c o n t r a s t t o t r e m b l i n g a s p e n , b i g t o o t h a s p e n g r o w s on d rie r sites an d t o l e r a t e s warm er t e m p e r a t u r e s . B igtooth a s p e n a p p e a r s t o o c c u r m o re f r e q u e n t l y t h a n tre m b lin g aspen on t h e f a r m l a n d o f M i c h i g a n ' s s o u t h e r n t i e r co unties (R eighard, of big to o th personal o b serv atio n ). fam ilies The h i g h e r g r o w t h r a t e s f r o m s o u t h e r n M i c h i g a n may b e d u e t o t h e co mmonly o b s e r v e d g e n e t i c t r e n d th a t so u th ern p o p u l a t i o n s o f many t r e e s p e c i e s s a c r i f i c e c o l d h a r d i n e s s for f a s t e r grow th r a t e s longer leaf reten tio n (W right 1976), o r i t may b e t h a t of the southern so u rces (R eighard, the 36 u npu b lish ed data) is an a d v a n t a g e b e c a u s e o f a u tu m n photosyn thesis. The b e s t h y b r i d f a m i l i e s had p a r e n t s o f b o th s p e c i e s fro m s o u t h e r n Lower M i c h i g a n . an d B a r n e s Barnes (1969) h a v e r e p o r t e d (1961) th at n atu ral i s c u r r e n t l y o c c u r r in g betw een b i g t o o t h in s o u th e r n M ichigan. species, an d A n d r e j a k h y b rid iza tio n an d t r e m b l i n g a s p e n Due t o t h i s g e n e f l o w b e t w e e n t h e two th e s o u th e r n M ichigan p o p u l a t i o n s o f t h e s e s p e c i e s p r o b a b l y s h a r e more g e n e s t h a n do t h e i r n o r t h e r n M i c h i g a n p o pulations. T his i n t r o g r e s s i o n may r e d u c e t h e d e g r e e o f chromosome n o n -h o m o lo g y in h y b r i d f a m i l i e s t h a t a r e p r o d u c e d fro m s o u t h e r n M i c h i g a n p a r e n t s b e c a u s e many n o n - v i g o r o u s h y b r id s in th e p l a n t a t i o n s suffered from a d y s g e n e s i s syndrome w hich i n c l u d e d c h l o r o p h y l l b reakdow n, bud a b o r t i o n , and s h o o t o r w h o le t r e e d e a t h . P a u l e y e t al^. (1 963c) found a s i m i l a r t y p e o f p h y s i o l o g i c a l ‘b r e a k d o w n when h e r e p o r t e d t h a t 39 o f 41 p r o g e n y o f a h y b r i d a s p e n f a m i l y d i e d a t a g e e i g h t f r o m unknown c a u s e s . ities an d P e t o ' s (1 93 8) These p h y s i o l o g i c a l fin d in g s t h a t h y brid abnorm al­ aspen p ro g en ies commonly h a v e c h r o m o s o m a l i r r e g u l a r i t i e s s u c h a s u n i v a l e n t s an d t r i v a l e n t s casts a s p e n o v e r an e n t i r e s u s p i c i o n on t h e f i t n e s s o f h y b r i d ro ta tio n p eriod. G eographic S e p a ra tio n of P a re n t S tands C ertain fa st-g ro w in g hy b rid aspen p ro g e n ie s X £ . g r a n d i d e n t a t a o r P. g l a n d u l o s a ; P. (ie. P^ a l b a t r e m u l a X P. t r e m u l o i d e s ) h av e been produced by c r o s s i n g Leuce p o p l a r s t h a t w e r e g e o g r a p h i c a l l y and e c o l o g i c a l l y d i s j u n c t ( Z s u f f a 37 1973). H ig h ly p r o d u c tiv e f a m i l i e s have a l s o been produced by h y b r i d i z i n g t h e s y m p a t r i c s p e c i e s P. a l b a an d P. t r e m u l a ( M o h r d i e k 1979b) an d a l l o p a t r i c (Johnsson 1956). In t h i s p o p u l a t i o n s o f P. stu d y , t h e r e w e r e no a p p a r e n t t r e n d s in th e biom ass p r o d u c tio n fa m ilie s of trem bling geographic d is ta n c e However, trem ula in d ic e s of the f u l l - s i b and h y b r i d a s p e n i n r e l a t i o n betw een th eir parents (Table to th e 2.6). t h e r e was a s m a l l d e c r e a s e i n t h e b i o m a s s p r o d u c tio n index of b i g t o o t h aspen f a m i l i e s w ith g e o g r a p h ic d i s t a n c e betw een th e p a r e n t s . sig n ifican t (P <.0 5) Johnsson (1956) co rrelatio n of variance T h i s t r e n d had a -.25. and M u h l e L a r s e n th a t n o n -ad d itiv e g en etic increasing (1970) h a v e a s s u m e d (heterosis) was r e s p o n s i b l e f o r th e grow th s u p e r i o r i t y of h y b r i d s betw een g eo g rap h ically iso lated absence of h e te r o s is a s p e n s p e c i e s and p o p u l a t i o n s . The i n t h e p r o g e n y t h a t w e r e p r o d u c e d by c ro ssin g g e o g ra p h ic a lly d i s t a n t p o p u la tio n s of trem b lin g a s p e n may b e a t t r i b u t e d to gene f lo w o c c u r r i n g betw een th e tre m b lin g aspen p o p u la tio n s a d d itiv e g en etic varian ce in grow th t r a i t s of aspen. in M ichigan. On t h e o t h e r h a n d , ( M o h r d i e k 1980) h a s b e e n r e p o r t e d If ad d itiv e effects were in d e e d im p o rta n t in th e perform ance of o u ts ta n d in g h y b rid fam ilies, t h e v a r i a t i o n w i t h i n M i c h i g a n ' s a s p e n p o p u l a t i o n s may h a v e been eq u al to or g r e a te r po p u latio n s. th an th e v a r i a t i o n betw een The l a r g e g e n e t i c v a r i a t i o n w i t h i n a s p e n p o p u l a t i o n s h a s b e e n w e l l d o c u m e n t e d by B a r n e s C heliak an d D a n c i k (1982), a n d many o t h e r s . (1969), T herefore, 38 maximum g e n e t i c g a i n c o u l d b e a c h i e v e d f r o m s e l e c t i n g w i t h i n one l a r g e , g e n e t i c a l l y t e s t e d p o p u l a t i o n . T ab le 2.6. B i o m a s s p r o d u c t i o n i n d e x i n % o f r e p l i c a t e mean of f a m i l i e s - w i t h i n - t a x a in r e l a t i o n to th e g e o g ra p h ic d i s t a n c e betw een p a r e n t s . P a r e n t a l T a xon D i s t a n c e (Km) Between P arents P. P. trem uloides X trem uloides O p en-po llinated 1-175 176-325 326-650 A verage P. g r a n d i d e n t a t a X P. g r a n d i d e n t a t a P. X s m i t h i i 114 132 121 130 77 50 46 45 84 90 76 121 59 84 The s l o w e r g r o w t h o f many JP. X s m i t h i i f a m i l i e s when c o m p a r e d t o p r o m i s i n g a s p e n h y b r i d s s u c h a s P. X r o u l e a u i a n a may b e i n d i r e c t l y t h e r e s u l t o f t h e p h e n o l o g i c a l i s o l a t i o n o f b i g t o o t h an d t r e m b l i n g a s p e n B a r n e s 1980) o v e r much o f t h e i r p henological b a r rie r ( P r e g i t z e r an d M ichigan r a n g e s . This to i n t r o g r e s s i o n e x e r t s upon e a c h s p e c i e s a form o f a s s o r t a t i v e m a tin g which h a s been d e m o n stra te d by G re g o riu s (1980) to be a p r o c e s s th at i n c r e a s e s t h e r a t e o f c h r o m o so m e e v o l u t i o n v i a a l l e l i c m u t a t i o n s and u l t i m a t e l y l e a d s to ch an g es in chromosomal h o m o l o g y b e t w e e n two p o p u l a t i o n s o r s p e c i e s . chromosomal irre g u la ritie s resp o n sib le for However, its The in t h i s h y b r id were p r o b a b l y in ferio r fitn e ss in th e pro g en y t e s t . another e x p la n a tio n for the lack of v ig o r i n P. 39 X sm ith ii sim ilar i s t h a t b o t h p a r e n t s p e c i e s may h a v e e v o l v e d u n d e r en v iro n m en tal c o n d i t i o n s in e a s t e r n N orth A m erica, a n d t h e r e f o r e , may b e m o re a l i k e g e n e t i c a l l y t h a n o t h e r aspen s p e c ie s used to produce h y b r id s . We do n o t know why i n c r e a s e d g e o g r a p h ic d i s t a n c e betw een b i g t o o t h p a r e n t s red u ced p rogeny p e rfo rm a n c e , b u t s a m p lin g e r r o r due to th e low number (34) o f f a m i l i e s a n a l y z e d c a n n o t b e r u l e d o u t . O p en -p o llin ated f a m il i e s of tre m b lin g aspen did not perform as w e ll as f u l l - s i b was t r u e for b ig to o th aspen. of the o p e n - p o llin a te d fam ilies. ( T a b l e 2.6) The o p p o s i t e The b i o m a s s p r o d u c t i o n index f a m i l i e s o f t r e m b l i n g a s p e n was 13 p e r c e n t b e l o w t h e mean b i o m a s s p r o d u c t i o n i n d e x o f i t s sib s. In c o n t r a s t t o fa m ilie s of bigtoo th fu ll-sib s. trem bling aspen, the o p e n -p o llin a te d a s p e n g r e w 29 p e r c e n t b e t t e r Farmer and B a rn e s o p en -p o llin ated (1978), found t h a t fam ilies. S ince open- f a m i l i e s u s u a l l y h a v e m o re t h a n o n e m a l e p a r e n t an d f u l l - s i b f a m i l i e s a r e f a t h e r e d by one m a le p a r e n t , would be e x p e c te d t h a t h a l f - s i b v ariatio n how ever, than i t s f a m i l i e s o f t r e m b l i n g a s p e n show ed no m o re g e n e tic v a r i a t io n than f u l l - s i b p o llin ated fu ll- in p h e n o ty p ic t r a i t s . nu m ber o f p o l l e n a d ifferen t it f a m i l i e s w o u l d show m ore We do n o t know why t h e p a r e n t s p e r f a m il y a f f e c t e d each s p e c i e s in m anner. H e r i t a b i l i t y and G e n e r a l Com bining A b i l i t y H e i g h t an d d i a m e t e r a n a l y s e s o f t h e two n e s t e d d e s i g n s sh o w ed t h a t t h e f e m a l e - w i t h i n - m a l e v a r i a n c e c o m p o n e n t was sig n ific a n t (P<.01), but t h e m a l e c o m p o n e n t was n o t . 40 N arrow -sense h e r i t a b i l i t i e s ( h 2 =.39) w e r e o b t a i n e d first for h eig h t from t h e ( h 2=.31) v arian ce com ponents o f th e n e s t e d d e s i g n which i n c l u d e d d a t a p lan tatio n . and d i a m e t e r from a s i n g l e H e r i t a b i l i t i e s c o u ld n o t be o b ta in e d from t h e s e c o n d d e s i g n w hich i n c l u d e d d a t a from t h r e e p l a n t a t i o n s b e c a u s e o f n e g a t i v e mean s q u a r e s observ atio n s from i n s u f f i c i e n t in th e sam p lin g p ro c e d u re s . The f i r s t n e s t e d d e s i g n g a v e r e l a t i v e l y sense h e r i t a b i l i t i e s and d i a m e t e r . (a d d itiv e g en etic The t r u e h e r i t a b i l i t y la r g e narrow - v ariance) fo r h eight of th ese t r a i t s l e s s becau se the genotype x environm ent i n t e r a c t i o n c o u l d n o t be p a r t i t i o n e d reported sim ilar a n d .3 5 ( d i a m e t e r ) L ikew ise, out. E i n s p a h r e t a ] .. narrow -sense h e r i t i b i l i t i e s for f u l l - s i b th eir h e r ita b ilitie s fam ilies of i s much v ariance (1967) o f .24 (height) trem bling aspen. w e r e b a s e d on a s i n g l e t e s t p lan tatio n . The n e s t e d d e s i g n a n a l y s e s show t h a t s e l e c t i o n o f t h e f e m a l e p a r e n t was i m p o r t a n t i n t h e m a t i n g d e s i g n . The c h o i c e o f t h e m a l e p a r e n t , h o w e v e r , was n o t f o u n d t o be sta tistic a lly m aternal im portant. e f f e c t or exp erim ental e r ro r . assumed b e c a u s e M ohrdiek m aternal T h i s may b e d u e t o a s t r o n g and p a t e r n a l P. t r e m u l a a n d p. (1979b) The l a t t e r reported t h a t both is the p a r e n t s were i m p o r t a n t in c r o s s e s of t r e m u l o i d e s , and i n t h e n e s t e d d e s i g n s , t h e b e t t e r m a l e s p o s s e s s e d good g e n e r a l c o m b i n i n g a b i l i t y (GCA). The t o p m a l e com bining a b ility in d e s i g n s 1 and 2 had a g e n e r a l (GCA) o f 1 8 . 5 an d 7 . 9 u n i t s above the 41 mean, resp ectiv ely . I n G er m an y , H a tte m e r and S e i t z (1967) f o u n d t h e GCA o f p a t e r n a l a s p e n p a r e n t s t o b e t h r e e t o f i v e t i m e s t h e GCA o f t h e m a t e r n a l a s p e n p a r e n t s crosses. in d i a l l e i T h e s e a n a l y s e s an d t h e t h e n a r r o w - s e n s e h e r i t a b i l i t y d a ta s u g g e st t h a t m ating d e s ig n s t h a t s c re e n f o r a d d i t i v e g e n e t i c v a r i a n c e s h o u ld be used to im prove th e b r e e d i n g p o p u l a t i o n o f Leuce p o p l a r s . A ge-age C o r r e l a t i o n s A g e - a g e c o r r e l a t i o n s b e t w e e n n u r s e r y h e i g h t an d t h e a v erag e tw o-year f i e l d h e ig h t w ith in each c ro ss p resented in T a b le 2.7. age-age c o r r e l a t i o n s M ohrdiek (1979a) are found p o s i t i v e o f .4 6 b e t w e e n y e a r s o n e a n d 20 an d .83 b e t w e e n y e a r s n i n e an d 20 f o r g r o w t h t r a i t s in aspen. A f t e r e v a l u a t i n g d a t a f r o m 36 a s p e n p r o g e n y t r i a l s , r ecom m end ed t h e e i g h t h y e a r a s t h e e a r l i e s t in ten sive se le c tio n . he tim e to begin The a g e - a g e c o r r e l a t i o n in t h i s study b e t w e e n n u r s e r y h e i g h t g r o w t h an d t h e h e i g h t g r o w t h a f t e r two f i e l d g r o w i n g s e a s o n s f o r a l l was s i g n i f i c a n t ( P < . 05) but aspen f a m i l i e s as a group s o m ew h at low (r= .48). F a m i l i e s o f t r e m b l i n g a s p e n and t h e t r i h y b r i d s ig n if ic a n t age-age c o r r e la tio n s , in c o n t r a s t to non­ s i g n i f i c a n t ones fo r b ig to o th aspen f a m il i e s . b ig to o th aspen as th e co rrelated , the Ta xa w i t h f e m a le p a r e n t were n o t s i g n i f i c a n t l y b u t t h e o p p o s i t e was t r u e fem ale p a re n t. had for tre m b lin g aspen as The a g e - a g e c o r r e l a t i o n o f f a m i l i e s w i t h a t r e m b l i n g a s p e n f e m a l e was l e s s s i g n i f i c a n t l y c o r r e l a t e d (P<.05) if t h e m a l e p a r e n t was b i g t o o t h aspen. One 42 explanation fo r th e d a ta is t h a t f a m il i e s of tre m b lin g aspen an d t h e t r i h y b r i d w e r e f a s t g r o w e r s t h e first few y e a r s s e e d , w h e r e a s b i g t o o t h a s p e n was a s l o w g r o w e r two y e a r s . years In t h e s e c o n d grow ing s e a s o n from s e e d ) , tre m b lin g aspen. in th e from fo r the first fie ld (th ree b i g t o o t h a s p e n began t o grow a s r a p i d l y a s This i n i t i a l s l o w s t a r t w o u l d e x p l a i n why t a x a w i t h b i g t o o t h a s p e n p a r e n t s h a d l o w an d n o n - s i g n i f i c a n t age-age c o r r e la ti o n s European w h ite p o p l a r a t an e a r l y a g e . (P. a l b a ) p a r e n t a g e h a d t h e age-age c o r r e l a ti o n of a l l largest t h e t a x a and w e r e t h e f a s t e s t g ro w in g in t h e n u r s e r y and t h e f i e l d T a b l e 2 .7. H ybrids c o n ta in in g plan tin g s. A g e - a g e c o r r e l a t i o n s o f t h e mean f a m i l y h e i g h t i n t h e n u r s e r y w i t h t h e mean f a m i l y h e i g h t averaged over four p la n t a t i o n s . Taxon ( F e m a l e X Male) F am ilies P e r Taxo n C o rrelatio n P opulus tre m u lo id e s X P. tre m u lo id e s 59 . 3 8 ** P. tre m u lo id e s X P. g r a n d i d e n t a t a 18 .51 * P. g r a n d i d e n t a t a X P. g r a n d i d e n t a t a 14 .33 n . s . P. g r a n d id e n ta ta X P. tre m u lo id e s 19 .28 n . s . (P. X ro u le a u ia n a ) X Populus s p e c ie s 17 .6 4 ** 127 . 4 8 ** A l l Ta xa * / * * S i g n i f i c a n t a t t h e 5 and 1 p e r c e n t l e v e l s , resp ectiv ely . 43 For s h o r t - r o t a t i o n biom ass p l a n t a t i o n s , sele ctio n w i t h i n t h i s p r o g e n y t e s t a t a g e t h r e e may b e e f f e c t i v e a t the s p e c ie s lev el (ie ., e lim in a te b ig to o th fam ilies), but s e l e c t i o n a t th e f a m i l y l e v e l would o n l y be p a r t i a l l y e ffe c tiv e u n til ap p ro x im ately year e ig h t. y e a r , many f a m i l i e s w o u l d b e f l o w e r i n g T h e re fo re , th e high ag e-ag e c o r r e l a t i o n s tra its an d p r e c o c i o u s flow ering By t h e e i g h t h ( V a l e n t i n e 1975). f o r grow th found in th e a sp e n s m ight p e r m i t an e i g h t - y e a r b r e e d i n g c y c l e w h i c h i s c o n s i d e r a b l y sh o rter t h a n many o t h e r tree sp ecies. 44 LITERATURE CITED A n d r e j a k , G . E . an d B . V . B a r n e s . 1969. A seed lin g population of a sp e n s in s o u t h e a s t e r n M ichigan. The M i c h i g a n B o ta n is t 8:189-202. B a r n e s , B.V . 1959. N a t u r a l v a r i a t i o n an d c l o n a l d e v e l o p m e n t o f P o p u l u s t r e m u l o i d e s and P . g r a n d i d e n t a t a i n n o r t h e r n Lower M i c h i g a n . P h . D . T h e s T s , U n i v . M i c h . , Ann A r b o r , M i c h i g a n . 334 p p . ______ . 1 9 6 1 . H ybrid asp e n s in th e lower p e n i n s u l a of M ichigan. Rhodora 6 3 :3 1 1 -3 2 4 . . 1966. The c l o n a l g r o w t h h a b i t o f A m e r i c a n a s p e n s . Ecology 4 7 :4 3 9 -4 4 7 . ______ . 1 9 6 9 . N a t u r a l v a r i a t i o n and d e l i n e a t i o n o f c l o n e s o f P o p u l u s t r e m u l o i d e s an d P . g r a n d i d e n t a t a i n n o r t h e r n Lower M i c h i g a n . S iT v a e G e n e t i c a 1 8 : 1 3 0 - 1 4 2 . B e n s o n , M.K. an d G. D u b e y . 1972. Aspen s e e d l i n g p r o d u c t i o n in a com m ercial n u r s e r y . I n s t . P a p . Chem. G e n e t . & P h y s i o l . N o t e s No. 1 2 , 7 p p . B e n s o n , M.K. an d D.W. E i n s p a h r . 1967. E a rly grow th of d i p l o i d , t r i p l o i d , and t r i p l o i d h y b r i d a s p e n . Forest S cience 13:150-155. C h e l i a k , W.M. a n d B . P . D a n c i k . 1982. G enic d i v e r s i t y o f n a t u r a l p o p u la tio n s of a c lo n e -fo rm in g t r e e Populus trem u lo id es. Can. J . G e n e t. C y to l. 2 4 :6 1 1 -6 1 6 . E i n s p a h r , D.W. a n d M.K. B e n s o n . 1964. P r o d u c t i o n an d e v a lu a tio n of aspen h y b rid s . J . F or. 62:806-809. . 1967. G eographic v a r i a t i o n W i s c o n s i n and U pper M i c h i g a n . of quaking aspen in S ilv a e G enet. 16:106-112. E i n s p a h r , D .W ., M.K. B e n s o n , and J . R . P e c k h a m . 1967. V a r i a t i o n and h e r i t a b i l i t y o f wood and g r o w t h c h a r a c t e r ­ i s t i c s of f i v e - y e a r - o l d quaking a sp en . I n s t . P a p . Chem. G e n e t . & P h y s i o l . N o t e s No. 1 , 6 p p . F a r m e r , M.M. and B.V. B a r n e s . 1978. M orphological v a r i a t i o n o f f a m i l i e s o f tr e m b l in g aspen in s o u t h e a s t e r n M ich ig an . The M i c h i g a n B o t a n i s t 1 7 : 1 4 1 - 1 5 3 . G r e g o r i u s , H.R. 1980. The e f f e c t o f p o s i t i v e a s s o r t a t i v e m a t i n g a t o n e l o c u s . P a r t 1: The g e n o t y p i c s t r u c t u r e o f the o ffs p rin g g e n e r a tio n . T heor. A ppl. G e n e t. 5 6 :1 8 7 -1 9 2 . 44 45 H a t t e m e r , H.H. a n d F.W. S e i t z . 1967. E i n i g e E r g e b n i s s e von T e s t a n b a u t e n m it A sp e n h y b rid e n . 2. Kreuzungen d e r J a h r e 1953 und 1 9 5 8 . S ilv a e G enetica 1 6 :6-13. H e n r y , R.M. a n d B . V . B a r n e s . 1977. C om parative r e p r o d u c tiv e a b i l i t y o f b i g t o o t h and t r e m b l i n g a s p e n and t h e i r h y b r i d . Can. J . B o t. 5 5 :3 0 9 3 -3 0 9 8 . Jo h n so n , L .P .V . 1942. S t u d i e s on t h e r e l a t i o n o f g r o w t h r a t e t o wood q u a l i t y i n P o p u l u s h y b r i d s . Can. J . R es. C. 2 0 : 2 8 - 4 0 . J o h n s s o n , H. 1956. H e te r o s is e r s c h e in u n g e n b e i H ybriden z w is c h e n B r e i t e n g r a d e n von P o p u lu s t r e m u l a . Z. F o r s t g e n e tik F o rs tp fla n z e n z . 5:156-160. . 1976. Das P r o d u k t i o n s p o t e n t i a l d e r H y b r i d a s p e n (P o p u l u s t r e m u l a x t r e m u l o i d e s ) i n S u d s c h w e d e n . H olzzucht 3 0 :1 9 -2 2 . K e l l y , R . P . , D . I . D i c k m a n n , J . W . W r i g h t , a n d W.A. Lemm ien. 1978. G e n e tic v a r i a t i o n o f e a s t e r n cottonw ood p l a n t e d in s o u th e rn M ichigan. M ich. S t a t e U n iv . A g r i c . E x p t . S t a . R e s . Rep . Mo. 3 6 2 . 6 p p . Kem perm an, J . A . 1976. Aspen c l o n e s : d e v e l o p m e n t , v a r i a b i l ­ i t y , an d i d e n t i f i c a t i o n . O n t . M in . N a t u r . R e s o u r c e s , F o r . R e s . I n f o r m . P a p . 1 0 1 . 11 p p . M a y n a r d , C.M. 1977. P r o d u c t i o n , c l o n a l p r o p a g a t i o n , and e v a l u a t i o n o f some P o p u l u s , s e c t i o n L e u c e , h y b r i d s . M.S. t h e s i s . Io w a S t a t e U n i v . , Ames, I o w a . 69 p p . M e l c h i o r , G.H. an d F.W. S e i t z . 1966. E inige E rgebnisse bei T e s ta n b a u te n m it A s p e n h y b rid e n . 1. K reuzungen d es J a h r e s 1951. S ilv a e G e n e tic a 15:127-133. M ichigan D ep artm en t o f A g r i c u l t u r e . M ichigan by s t a t i o n s . 2nd. ed . 1971. C lim ate of L a n sin g , M ichigan. M ohrdiek, 0. 1979a. J u v e n i l e - m a t u r e an d t r a i t c o r r e l a t i o n s i n some a s p e n a n d p o p l a r t r i a l s . S i l v a e G e n e t i c a 28: 107-111. 1979b. P r o g e n y t e s t s w i t h L e u ce p o p l a r s in Germany: c r o s s i n g s w i t h i n and b e t w e e n s p e c i e s , an d b a c k c r o s s i n g s . K o m m i s s i o n s v e r l a g B u c h h a n d l u n g Max W i e d e b u s c h , Ham bur g. . 1980. U n te r s u c h u n g e n z u r E ignung von A s p e n e l t e r n f u r d ie K reuzungszuchtung. H olzzucht 3 5 :5 -9 . _ _ . M u h l e - L a r s e n , C. 1970. Recent advances I n t e r n a t . Rev. o f F o r . R e s . 3 : 1 - 6 7 . in p o p l a r b r e e d i n g . 46 O k a f o , O.A. 1976. C o m p a r a tiv e p h y s i o l o g y and d e v e lo p m e n t of t r e m b l i n g a s p e n (P o p u l u s t r e m u l o i d e s M i c h x . ) an d b i g t o o t h a s p e n (P o p u lu s g r a n d i d e n t a t a M ich x .) from M ichigan p o p u l a t i o n s . P h . D . t h e s i s . M ic h . S t a t e U n i v . , E a s t L a n s i n g , M i c h i g a n 103 p p . P au ley , S .S . 1949. F o re st-tre e gen etics Economic B o ta n y 3 : 2 9 9 - 3 3 0 . research: P o p u l u s L. ______ . 1956. N atu ral h y b r id iz a tio n of the aspens. M in n . F o r . N o t e s No. 4 7 . 2 p p . U niv. P a u l e y , S . S . an d T . O . P e r r y . 1954. E cotypic v a r i a t i o n of th e p h o t o p e r i o d i c re s p o n s e in P o p u lu s . J . A rnold A rb o r. 35:167-188. P a u l e y , S . S . , A.G. J o h n s o n , an d F . S . S a n t a m o u r , J r . 1963a. R e s u l t s o f a s p e n s c r e e n i n g t e s t s : I . Seed s o u r c e s o f q u ak in g aspen (P. t r e m u l o i d e s M ic h a u x ). U n i v . M in n . F o r . N o t e s No. 1 3 6 . 2 p p . 1963b. R e s u l t s o f a s p e n s c r e e n i n g t e s t s : I I . Seed s o u r c e s o f E u r o p e a n a s p e n (P o p u l u s t r e m u l a L i n n a e u s ) . U n i v . M in n . F o r . N o t e s No. 1 3 7 . 2 p p . . 1963c. R e s u l t s o f a s p e n s c r e e n i n g t e s t s : I I I . F^ h y b r id p r o g e n ie s o f quaking x Europeana s p e n . Univ. M in n . F o r . N o t e s No. 1 3 8 . 2 p p . _ _ . P eto, F.H . 1938. C ytology o f h y b rid s. C a n . J . R e s . C. p o p l a r s p e c i e s an d n a t u r a l 16:445-455. P r e g i t z e r , K .S . and B.V. B a r n e s . 1980. F low ering phenology o f P o p u l u s t r e m u l o i d e s an d P o p u l u s g r a n d i d e n t a t a and the p o te n tia l fo r h y b r id iz a tio n . C a n . J . F o r . R e s . 10: 218-223. R a n d a l l , W.K. an d D . T . C o o p e r . 1973. P re d ic te d genotypic g a i n from c o tto n w o o d c l o n a l t e s t s . S i l v a e G e n e tic a 22: 165-167. V a l e n t i n e , F.A . 1975. G e n e tic c o n t r o l of sex r a t i o , e a r l i n e s s an d f r e q u e n c y o f f l o w e r i n g i n P o p u l u s trem u lo id es. P r o c . o f 22nd N o r t h e a s t e r n F o r e s t T r e e I m p r o v e m e n t C o n f e r e n c e . S . U . N . Y . S y r a c u s e , N.Y. pp. 111-129. W right, j .w . 1976. A c a d e m ic P r e s s , I n tr o d u c tio n to F o re s t G e n e tic s . New Y o r k . 463 p p . Y i n g , C . C . a n d W.T. B a g l e y . 1976. G enetic v a r i a t io n of e a s t e r n cottonw ood in e a s t e r n N ebraska p ro v en an ce s tu d y . S ilv a e G enetica 25:67-73. 47 Z s u f f a , L. 1973. A summary r e v i e w o f i n t e r s p e c i f i c b r e e d i n g in t h e g en u s P o p u lu s . IN/ P r o c . o f th e 1 4 th m e e tin g o f t h e C an a d ia n T re e Improvement A sso c. D . P . F o w l e r and C.W. Y ea tm a n ( E d i t o r s ) . F r e d e r i c t o n , N.B. p p . 1 0 7 - 1 2 3 . CHAPTER 3 G e n e tic A nalyses of F i f t e e n P h e n o lo g ic a l, P hysio lo g ical, and M o r p h o l o g i c a l T r a i t s P o p u lu s g r a n d i d e n t a t a , P. in t r e m u l o i d e s , and T h e i r H y b r i d s ( P a p e r t o b e p r e s e n t e d a t t h e 1985 N o r t h C e n t r a l T r e e I m p r o v e m e n t C o n f e r e n c e a t E a s t L a n s i n g , MI) ABSTRACT A com bination h a l f - s i b / f u l l - s i b progeny t e s t of Populus g r a n d i d e n t a t a , P. t r e m u l o i d e s , a n d t h e i r a t four lo catio n s su scep tib ility tra its in M ichigan. a n d P. co n sid e rab le a d d itiv e g en etic leafed out e a r lie r fall N in e t r a i t s t o s i x p e s t s were exam ined. i n P. g r a n d i d e n t a t a den tata. h y b r i d s was p l a n t e d and P henological trem uloides ex h ib ited variance. and d r o p p e d l e a v e s JP. t r e m u l o i d e s later than £. g ra n d i­ H y b r i d p h e n o l o g y was i n t e r m e d i a t e . D ate o f l e a f and t h e l e a f a r e a d u r a t i o n p e r i o d w ere s i g n i f i c a n t l y c o r r e l a t e d w ith grow th p erfo rm an ce. M orphological t r a i t s su ch a s autumn l e a f c o l o r , b r a n c h i n e s s , and bud c h a r a c t e r i s ­ t i c s h a d b o t h a d d i t i v e an d n o n - a d d i t i v e g e n e t i c v a r i a n c e . For t h e s e t r a i t s , h y b r i d s r e s e m b l e d t h e m a t e r n a l p a r e n t m o re so th a n th e p a t e r n a l p arent. of d iso rd e rs in clu d in g ad v en titio u s sp routing. H ybrids s u f f e r e d f r o m a nu mber s h o o t d i e b a c k , bud a b o r t i o n , and S a p e r d a i n o r n a t a an d V e n t u r i a tr e m u l a e were th e m ost s e r i o u s i n s e c t and d i s e a s e p r o b l e m s . G e n e t i c r e s i s t a n c e o f a p h y s i o l o g i c a l n a t u r e t o i n s e c t s and d i s e a s e s was n o t f o u n d . su scep tib ility ex isted However, d ifferen ces in among f a m i l i e s a n d s p e c i e s . 48 49 INTRODUCTION The i n c r e a s i n g r e l i a n c e on a r t i f i c i a l r e g e n e r a t i o n by t h e m a j o r f o r e s t r y c o m p a n i e s t o p r o d u c e h i g h - q u a l i t y wood f i b e r has expanded t h e m a rk e t f o r g e n e t i c a l l y im proved p la n tin g sto ck of co m m ercially v a l u a b le tr e e s p e c ie s . b r e e d e r s h a v e b e e n somewhat s u c c e s s f u l i n f u l f i l l i n g i n d u s t r y 's needs by l o c a t i n g f a m i l i e s o f many t r e e testin g trees the s u p e r i o r p o p u l a t i o n s and s p e c i e s t h r o u g h p r o v e n a n c e and p r o g e n y and e s t a b l i s h i n g (W right 1976). Tree seed o rch ard s w ith th e se s e le c te d From t h e e a r l y s o u t h e r n p i n e s e e d o r c h a r d s , maximum g e n e t i c g a i n s a b o v e c o m m e r c i a l n u r s e r y s t o c k o f 32% f o r l o b l o l l y p i n e ( W e i r 1 9 8 3 ) a n d 45% f o r s l a s h pine ( K o s s u t h ^ t a_l. generation 1982) h a v e b e e n r e p o r t e d . seed o r c h a r d s h av e a l r e a d y been p l a n t e d w ith seed p ro d u c e d from m a t i n g s o f s u p e r i o r However, Second first generation fam ilies. th e o r i g i n a l g erm plasm b a s e would soon s h r i n k i f c o n tin u e d m atin g o c c u r r e d betw een s u p e r i o r fam ilies or t h e i r progeny. To m a i n t a i n p o t e n t i a l l y i n c o r p o r a t e new o n e s , p o o l of th e i n i t i a l or s p e c ie s . successful in some g e n e t i c i s t s d i v e r s i f y th e gene b r e e d i n g p o p u l a t i o n by h y b r i d i z i n g r a c e s H y b r i d iz a t io n betw een s p e c i e s has been in in c r e a s in g secondary t r a i t s etc.) i m p o r t a n t g e n e s an d t o the g e n e tic v a r i a t i o n of im p o rtan t (ie .f fo lia g e c o lo r, the genera P icea (La F a r g e and K r a u s 1980), disease resistan ce, (K u d ray an d H a n o v e r 1 9 8 0 ) , and P o p u l u s (Zsuffa 1973). H o w e v e r , g e n e s f o r s o m e o f t h e s e t r a i t s a r e l o s t when P inus 50 s e l e c t i o n s t r a t e g i e s em phasize o n l y th e a v e r a g e grow th r a t e of each fa m ily . T his is u n d e s ir a b le c o n s id e rin g secondary t r a i t s such as phenology 1970), co ld -h ard in ess d isease re sis ta n c e arch itectu re avoidance th at ( N i e n s t a e d t an d K in g ( S a k a i and W e i s e r 1 9 7 3 ) , ( P o w e r s an d K r a u s 1983), ( I s e b r a n d s an d N e l s o n 1 9 8 2 ) , i n s e c t and crown an d d r o u g h t ( P e r e i r a a n d K o z l o w s k i 1976) h a v e b e e n shown t o s i g n i f i c a n t l y a f f e c t g r o w t h and s u r v i v a l o f c o m m e r c i a l t r e e sp ecies. Tree b r e e d e r s o f te n m ating th e t a l l e s t gain trees w ill in th e s h o r t e s t tim e. t a k e t h e myopic view t h a t a lw a y s g i v e t h e most g e n e t i c Instead, g en eticists need to i n v e s t i g a t e t h e p h e n o l o g i c a l , p h y s i o l o g i c a l , and m orphological tra its secondary t r a i t s c o n c u r r e n t l y w ith gro w th r a t e so t h a t t h a t a f f e c t g row th r a t e can be i d e n t i f i e d . In a d d i t i o n , knowing t h e h e r i t a b i l i t y v a r ia n c e o f each t r a i t genes fa c ilita te s in to th e breeding an d t y p e o f g e n e t i c the in c o r p o ra tio n of i t s p o pulation. The o b j e c t i v e s o f t h i s s t u d y w e r e t o i n v e s t i g a t e r e l a t i o n s h i p betw een t h r e e p h e n o l o g i c a l the t r a i t s and t h e tw o - y e a r g r o w t h p e r f o r m a n c e o f 206 f a m i l i e s o f P o p u l u s g r a n d i d e n t a t a , P. t r e m u l o i d e s , an d t h e i r h y b r i d s M ichigan p l a n t a t i o n s . in ter- In a d d i t i o n , an d i n t r a s p e c i f i c in terp retatio n s tiv e data. tra its p h y sio lo g ical, and w e r e made b a s e d upon e i t h e r q u a n t i t a ­ (nested d esig n a n a ly se s) L astly , of i n h e r i t a n c e p a t t e r n s an d g e n e t i c v a r i a n c e com ponents o f n in e p h e n o l o g i c a l , m orphological in f o u r resistan ce or q u a l i t a t i v e (mean r a n k s ) t o s i x a s p e n p e s t s was e v a l u a t e d . 51 MATERIALS AND METHODS M easurem ents Nine t r a i t s w e r e q u a n t i t a t i v e l y m e a s u r e d i n 1982 an d 1983 i n f o u r M i c h i g a n p l a n t a t i o n s o f a c o m b i n a t i o n h a l f sib /fu ll-sib a s p e n p r o g e n y t e s t o f P o p u l u s g r a n d i d e n t a t a , P. t r e m u l o i d e s , P. X s m i t h i i , an d b a c k c r o s s e s leau ian a. s i t e s an d p r o g e n y t e s t h a v e b e e n The p l a n t a t i o n p r e v i o u s l y d e s c r i b e d by R e ig h a r d (1984). w e r e t i m e o f l e a f f l u s h an d l e a f f a l l , autumn l e a f c o l o r , o rie n ta tio n dieback, The n i n e t h e nu m ber o f p r i m a r y b r a n c h e s , b u d from t h e ste m , bud s c a l e p u b e s c e n c e , s h o o t sprouts. s i x asp en p e s t s were e v a l u a t e d s h o o t s an d l e a v e s : th e "sh e p h e rd 's crook" In f o r da m age t o fungus t r e m u l a e ) , an u n i d e n t i f i e d v i r u s l e a f s p o t , b eetle tra its le a f area d u ratio n , an d t h e p r e s e n c e o f r o o t c o l l a r ad d itio n , t o P. X r o u - (V e n t u r i a the p o p l a r - g a l l (S a p e r d a i n o r n a t a ) , t h e w i l l o w s h o o t s a w f l y a b b r e v ia tu s ) , the p o p la r the w h i t e t a i l deer tentm aker (C l o s t e r a (J a n u s i n c l u s a ) , and (O d o c o i l e u s v i r g i n i a n u s ) . The n i n e t r a i t s an d t h e l e a f s p o t an d w i l l o w s h o o t s a w f l y dam ag e w e r e m e a s u r e d o r r e c o r d e d a t t h e E a s t L a n s i n g p lan tatio n (In g h am C o ., L a t . 4 2 .7 °N , Long. 84.5°W ). b r o w s i n g an d t h e nu m b er o f S a p e r d a g a l l s scored 43.5°N, at the L ong. was t a l l i e d 4 2 . 0 °N , Lon g. were co u n ted Six Lakes p l a n t a t i o n 85.2°W). at 86.0°W). p e r t r e e were ( M e c o s t a Co ., L at. D e f o l i a t i o n by t h e p o p l a r th e D ecatur p l a n t a t i o n L astly , ( C a s s Co ., tentm aker L at. V enturi a- in f e c te d in t h e Chatham p l a n t a t i o n Deer ( A l g e r Co ., sh o o ts L at. 52 4 6 . 3 ° N f Lon g. Lansing test 86.9°W) as w e ll as a t the S i x L a k e s an d E a s t site s. L e a f f l u s h d a t a w ere r e c o r d e d a s th e number of d a y s a f t e r May 1, 1983 u n t i l lead er. l e a f f l u s h o c c u r r e d on t h e t e r m i n a l T r e e s w e r e s c o r e d a s l e a f e d o u t when t h e f i r s t leaf h a d e m e r g e d f r o m t h e t e r m i n a l bud an d was c o m p l e t e l y u n ro lled . The t r e e s w e r e s c o r e d e v e r y f o u r t h d a y . The l e a f f a l l m e a s u r e m e n t i n t h i s s t u d y was e q u a t e d w ith th e l o s s of p h o t o s y n t h e t i c a l l y - a c t i ve f o l i a g e . Leaf f a l l d a t a w ere r e c o r d e d a s th e number o f d a y s a f t e r S e p t e m b e r 1 , 1 9 8 2 u n t i l e a c h t r e e h a d e i t h e r l o s t 90% o f i t s g r e e n l e a v e s , o r 90% o f i t s l e a v e s h a d c h a n g e d t o t h e i r autumn c o l o r . T re e s were v i s i t e d e v e r y s e v e n th day. Leaf a r e a d u r a t i o n was c a l c u l a t e d b y summing t h e d a y s b e t w e e n t h e dates o f l e a f f l u s h an d l e a f f a l l fo r each t r e e . Autumn l e a f c o l o r o f e a c h t r e e was j u d g e d t o be o n e o f f i v e c o l o r s : (1) y e l l o w , and (5) r e d . (2) y e l l o w - o r a n g e , if the (3) orange, l e a v e s on a t r e e turned (4) orange-red, from g r e e n to b r o w n o r b l a c k , i t w a s r e c o r d e d a s h a v i n g no p i g m e n t co lo ratio n . The n u m ber o f p r i m a r y b r a n c h e s o r i g i n a t i n g cen tral the stem o f each t r e e were c o u n te d . l a t e r a l b u d s on t h e t e r m i n a l e ith e r appressed (in c lin ed shoot. or > 5 0 (p arallel from t h e The c e n t e r a x e s o f l e a d e r were s c o r e d as or in c lin e d inward) or d i v e r g e n t outw ard) w i th r e s p e c t t o th e a x i s o f th e t e r m i n a l The t e r m i n a l percent of its bud was s c o r e d a s h a v i n g e i t h e r bud s c a l e s 0, < 5 0 , showing d e n s e p u b e s c e n c e . 53 S h o o t d i e b a c k f r o m p h y s i o l o g i c a l d y s g e n e s i s was r e c o r d e d t h e s p r i n g o f 1 983. s p r o u t s was n o t e d . sprouting in A lso, the presence of ro o t c o l l a r The a m o u n t o f s h o o t d i e b a c k on e a c h a f f e c t e d and t r e e was n o t r e c o r d e d . The v i r u s l e a f s p o t an d V e n t u r i a t r e m u l a e d i s e a s e s w e r e scored June, fo r each t r e e 1982. as e i t h e r p r e s e n t or a b s e n t du rin g The n u m b e r o f t e r m i n a l and s p r o u t s h o o t t i p s g i r d l e d by t h e w i l l o w s h o o t s a w f l y were t a l l i e d Ju n e and J u l y o f 1983. throughout The n u m b er o f S a p e r d a g a l l s p e r t r e e a n d t h e nu m ber o f t r e e s b r o w s e d b y d e e r w e r e c o u n t e d Septem ber, 1983. A lso, t r e e s of each s p e c ie s tentm aker in Septem ber, in 1983 t h e nu m b er o f t h a t w ere d e f o l i a t e d by t h e p o p l a r were r e c o r d e d . S t a t i s t i c a l A nalyses A n a l y s e s o f v a r i a n c e were c a l c u l a t e d from p l o t means a t t h e f a m i l y and s p e c i e s m easured. lev el for the four leaf tr a its P e a r s o n c o r r e l a t i o n s were c a l c u l a t e d r e l a t i o n s h i p s betw een th e l e a f f l u s h , area d u ratio n d ata. leaf f a l l , grow th m easurem ents r e p o r t e d l e a f c h a r a c t e r s an d t h e by R e i g h a r d (1984) f o r N arrow -sense h e r i t a b i l i t i e s com bining a b i l i t y and l e a f C o r r e l a t i o n s were a l s o c a l c u l a t e d f o r th e a s s o c i a t i o n betw een t h e s e progeny t e s t . fo r the (GCA) w e r e c a l c u l a t e d an d l e a f c o l o r d a t a f o r a n e s t e d d e s i g n D e s i g n 1) o f 32 f a m i l i e s L ansing p l a n t a t i o n . (8 m a l e s , th is an d g e n e r a l from t h e l e a f f l u s h (North C a r o l i n a 28 f e m a l e s ) from t h e E a s t 54 The d a t a c o l l e c t e d from t h e o t h e r e l e v e n c h a r a c t e r s t h i s s tu d y were n o t n o r m a l l y d i s t r i b u t e d in according to th e K o l m o g o r o v - S m i r n o v o n e - s a m p l e t e s t f o r n o r m a l i t y ( H u l l and Nie 1981); (S teel th erefo re, F ried m an 's an d T o r r i e 1960) tw o - w a y c l a s s i f i c a t i o n for non-param etric data test from a r a n d o m i z e d b l o c k d e s i g n was u s e d t o d i s c e r n d i f f e r e n c e s betw een s p e c i e s . F urtherm ore, K e n d a ll's rank c o r r e l a t i o n f o r n o n - p a r a m e t r i c d a t a was u s e d t o d e t e c t o f b ra n c h number, the e f f e c t s S a p e r d a i n o r n a t a , V e n t u r i a t r e m u l a e , and d e e r b r o w s i n g u p o n t h e h e i g h t an d d i a m e t e r g r o w t h i n t h e p lan tatio n s. RESULTS AND DISCUSSION L eaf Phenology H i g h l y s i g n i f i c a n t d i f f e r e n c e s were found in p h e n o l o g y b e t w e e n an d w i t h i n t h e a s p e n s p e c i e s an d h y b r i d s (T a b le 3.1). T rem bling aspen f a m i l i e s and in e f f e c t , out e a r l i e r , retained th e ir leaves grow ing se a so n i n c o m p a r i s o n t o t h e b i g t o o t h and h y b r i d fam ilies. longer, flu sh ed ha d t h e lo n g est On t h e o t h e r h a n d , p h e n o l o g y o f b i g t o o t h a s p e n f a m i l i e s was j u s t t h e o p p o s i t e . midway b e t w e e n the The h y b r i d f a m i l i e s were p aren ts. The a v e r a g e t i m e p e r i o d f o r l e a f f l u s h i n g an d l e a f f a l l i n a l l t a x a w a s 12 d a y s f o r l e a f f l u s h a n d 21 d a y s f o r l e a f fa ll. A lth o u g h th e h y b r i d s were g e n e r a l l y i n t e r m e d i a t e phenology, some P. Xs m i t h i i or dropped t h e i r fam ilies e ith e r leaves e a r lie r t r e m b l i n g an d b i g t o o t h a s p e n . than a l l The l a t e flu sh ed in later f a m il i e s of both flu sh in g tim e Table 3 .1 . L e a f f l u s h , l e a f f a l l , and l e a f a r e a d u r a t i o n i n p e r c e n t o f r e p l i c a t e mean a t t h e E a s t L a n s i n g p l a n t a t i o n f o r t h e e a r l i e s t and l a t e s t p h e n o l o g i c a l f a m i l i e s o f P. t r e m u l o i d e s , P. g r a n d i d e n t a t a , P. X s m i t h i i , and P. X r o u l e a u i a n a b a c k c r o s s e s . Leaf Flush^ Taxa E a rlie s t L atest Leaf F a l l 2 X E a r lie s t L atest L e a f A r ea D u r a t i o n 3 X Minimum Maximum x 9. P .tre m u lo id e s 43 111 80 89 126 107 97 112 104 (P .X rouleauiana) X P .trem u lo id es 60 120 86 70 107 96 89 105 100 P .X sm ithii 61 256 118 66 107 96 83 105 98 (P .X rouleauiana) X P .g ra n d id e n ta ta 99 136 112 77 104 92 92 101 96 P .g ra n d id e n ta ta 97 161 126 70 104 92 86 102 95 S ignificance o f F -value ** ** ** ** S i g n i f i c a n t a t t h e 1% l e v e l o f p r o b a b i l i t y . 1 Mean value of a l l fam ilies (100%) = 14 d a y s fro m May 1 s t (May 1 4 t h ) . 2 Mean value of a l l fam ilies (100%) = 61 d a y s fro m S e p t e m b e r 1 s t 3 Mean value of a l l fam ilies (100%) = 170 d a y s . (October 3 1 st). 56 (3 w e e k s l a t e r t h a n t h e m e a n f o r a l l hy brid fam ilies) o f some f a m i l i e s was p r o b a b l y d u e i n p a r t t o a b n o r m a l i t i e s i n t h e g e n e r e g u l a t i o n o f c y t o k i n i n p r o d u c t i o n and tran slo catio n , s in c e the p ro d u c tio n of c y t o k i n i n - l i k e s u b sta n c e s has been d em onstrated flu sh in g in s p e c i e s o f P o p u lu s H e w l e t t and W a r e i n g 1 9 7 3 ) . h ybrid fam ilies (Domanski an d K o z l o w s k i 1 9 6 8 , The e a r l y (3 w e e k s e a r l i e r f a m i l i e s ) may r e s u l t t o b e a s s o c i a t e d w i t h bud l e a f d r o p o f some t h a n t h e mean f o r a l l from a p r e m a t u r e i n c r e a s e in e t h y l e n e p r o d u c t i o n d u e t o an i m b a l a n c e b e t w e e n a b s c i s i c a c i d and grow th p ro m o ter hormones. The l e a f a b e r r a n t f a m i l i e s was a s l i t t l e p l a n t a t i o n mean o f a l l area d u ra tio n of these a s 29 d a y s l e s s than the fam ilies. D a t e o f l e a f f l u s h o f t h e f a m i l i e s was s i g n i f i c a n t l y c o r r e l a t e d a t t h e 1% l e v e l w i t h d a t e o f l e a f f a l l an d t h e length D ate o f l e a f w ith the of the leaf f a l l was a l s o leaf thus have a longer reported s im ila r period (r = - .7 7 ) . sig n ific a n tly co rrelated area d u ra tio n period f a m i l i e s w e r e m o re l i k e l y in n o rth e rn area d u ratio n {r = - . 3 8 ) (r = .86). to drop t h e i r leav es le a f area d u ra tio n period. (P < .01) E arly le a fin g l a t e r an d B a r n e s (1 969 ) fin d in g s fo r th re e tre m b lin g aspen c lo n e s M ichigan. The e a r l y f l u s h i n g o f many t r e m b l i n g a s p e n f a m i l i e s , when c o m p a r e d t o t h e b i g t o o t h greater sen sitiv ity f a m i l i e s , may b e d u e t o to tem p eratu re. L a te w i n t e r and e a r l y s p r i n g t e m p e r a t u r e s a r e known t o i n f l u e n c e t h e p h y s i o l o g i c a l processes th at co n tro l le a f flu sh in g i n many t r e e s p e c i e s 57 (Kramer an d K o z l o w s k i 1 9 7 9 ) . sy n th esis req u ire Genes t h a t reg u late hormone i n t h e r o o t s a n d b u d s o f t r e m b l i n g a s p e n may l o w e r minimum t e m p e r a t u r e s t h a n s i m i l a r g e n e s b i g t o o t h a s p e n b e f o r e t h e y become a c t i v a t e d . A nother h y p o th e s is fo r th e s p rin g phenology d i f f e r e n c e s aspens is in in th e t h a t t h e breakdow n o f i n h i b i t o r hormones o c c u r s m o re r a p i d l y i n t r e m b l i n g a s p e n a s t h e t e m p e r a t u r e s warm above fre e z in g . S i n c e m o s t P. X s m i t h i i f a m i l i e s b e t w e e n t h e two s p e c i e s a d d itiv e gen etic for th is phen o lo g ical fell character, v a r i a n c e was a s s u m e d t o b e i n v o l v e d . However, t h e u n u s u a l l y l a t e f l u s h i n g t i m e s o f some h y b r i d f a m i l i e s c o u l d b e t h e r e s u l t o f e p i s t a t i c e f f e c t s o r genome in co m p atib ility . On t h e o t h e r h a n d , the l e a f f a l l r e s u lts suggest th a t b i g t o o t h a s p e n an d m o s t h y b r i d s w e r e m o r e s e n s i t i v e trem bling than aspen to d e c re a s in g p h o to p e rio d because th ey dropped t h e i r leav es e a r lie r . These d a t a im p l i e d t h a t each s p e c i e s was s e n s i t i v e t o d i f f e r e n t e n v i r o n m e n t a l s t i m u l i . However, i f decreasing seasonal t e m p e r a t u r e s a r e more im p o rta n t than d a y le n g th changes, i t w o u l d t h e n see m l o g i c a l t h a t tre m b lin g aspen should drop i t s th e h y p o th e s is t h a t gene a c t i v a t i o n occurs a t low er t e m p e r a tu r e s leav es l a t e r because of o f hormone s y n t h e s i s in t r e m b l i n g asp en . A p h y s i o l o g i c a l a d a p t a t i o n to low er g ro w in g -se a so n t e m p e r a t u r e s would be b e n e f i c i a l as trem bling much o f i t s for a b o re a l s p e c ie s such a s p e n s i n c e c o o l n i g h t s a r e common t h r o u g h o u t n a tiv e range. 58 The n a r r o w - s e n s e h e r i t a b i l i t i e s calcu lated from t h e n e s te d d e s ig n d a ta a t th e E a s t Lansing p l a n t a t i o n g av e a h e rita b ility o f 0.17 f o r leaf flu sh . H e rita b ilitie s from th e l e a f d ro p d a t a c o u ld n o t be c a l c u l a t e d b e c a u se o f n e g a t i v e mean s q u a r e s f r o m e x p e r i m e n t a l e r r o r design. in th e m ating However, t h e f e m a l e - w i t h i n - m a l e v a r i a n c e com ponent was h i g h l y s i g n i f i c a n t f o r b o t h p h e n o l o g i c a l c h a r a c t e r s , w h e r e a s t h e m a l e c o m p o n e n t was s t a t i s t i c a l l y non­ sig n ific a n t . D esp ite the s t a t i s t i c a l p a r e n ts in th e d e s ig n , in m ale e f f e c t s i n s i g n i f i c a n c e of th e m ale t h e r e was s t i l l (general com bining a b i l i t y ) e a r l i e s t and l a t e s t m a l e s f o r l e a f com bining a b i l i t i e s a siz a b le d ifferen ce flu sh . betw een th e The g e n e r a l (GCA) o f t h e e a r l i e s t a n d l a t e s t m a l e s f o r l e a f f l u s h a v e r a g e d - 2 3 a n d 30 p e r c e n t f r o m t h e m e a n , resp ectiv ely . e a r l y or l a t e G a i n s c o u l d b e made i n b r e e d i n g f o r e i t h e r f lu s h in g genotypes. In a d d itio n to th e l a r g e v a r i a t i o n in p h e n o lo g y betw een a n d w i t h i n t h e a s p e n s p e c i e s an d h y b r i d s , latitu d in al t h e r e was a l s o a o r p h o t o p e r i o d i c r e s p o n s e shown b y f a m i l i e s f r o m d i f f e r e n t l a t i t u d e s a t th e E a st Lansing p l a n t a t i o n 3.2). Trem bling latitu d e th is fam ilies from n o r t h f l u s h e d up t o 13% e a r l i e r latitu d e. d iffered aspen only dropped t h e i r the fa m ilie s . (T able o f 44.2°N than f a m i l i e s south of L e a f d r o p among t r e m b l i n g a s p e n f a m i l i e s in t h e Upper P e n i n s u l a leav es (UP) s o u r c e s w h i c h th ree percent e a r l i e r than the r e s t of The l e a f a r e a d u r a t i o n p e r i o d f o r t h e s e UP 59 f a m i l i e s was a l s o th ree percent le ss. In b i g t o o t h a sp en , t h e U p p e r P e n i n s u l a f a m i l i e s f l u s h e d much l a t e r Lower P e n i n s u l a s o u r c e s a n d d r o p p e d t h e i r had s h o r t e r sources. l e a v e s e a r l i e r an d l e a f a r e a d u r a t i o n p e r i o d s t h a n Lower P e n i n s u l a These s h o r t co n trib u ted than th e l e a f r e te n tio n p erio d s undoubtedly t o t h e p o o r g r o w t h o f UP b i g t o o t h f a m i l i e s in th e s o u th e r n M ichigan p l a n t a t i o n s . T a b l e 3.2. Region P h en o lo g y d i f f e r e n c e s in p e r c e n t o f r e p l i c a t e mean o f t r e m b l i n g and b i g t o o t h a s p e n h a l f - s i b f a m i l i e s from d i f f e r e n t l a t i t u d i n a l r e g i o n s in M ichigan a t th e E a s t L ansing p l a n t a t i o n . L atitu d e Leaf F lush S pecies Leaf F all L eaf Area D uration ---------- %_. 1 2 3 4 4 1 . 8 - 4 3 . 0°N 4 3 . 0 - 4 4 . 2°N 4 4 . 2 - 4 5 . 8°N 45 . 8 - 4 7 . 0°N P .trem u lo id es Do. Do. Do. 1 2 3 4 4 1 . 8 - 4 3 . 0°N 4 3 . 0 - 4 4 . 2°N 4 4 . 2 - 4 5 . 8°N 45 . 8 - 4 7 . 0°N P .g ra n d id e n ta ta Do. Do. Do. 83 87 74 75 102 102 102 99 104 104 104 101 117 120 122 142 100 98 99 93 98 95 98 89 The e a r l y f l u s h i n g o f t r e m b l i n g a s p e n f a m i l i e s f r o m ty p ically colder r e g io n s of M ichigan i s p r o b a b l y an a c c e l e r a t e d stim u lu s. In c o n t r a s t , ( n o r t h o f 4 4 .2 °N l a t . ) re sp o n se to th e te m p e ra tu re in itia tio n of le a f senescence p r o c e s s e s a p p e a r s t o d e p e n d m o re on a p h o t o p e r i o d s t i m u l u s because th e n o rth ern m o st th eir fam ilies ( n o r t h o f 45.8°N) l e a v e s e a r l y a t th e E a st Lansing s i t e . dropped However, 60 tem perature e f f e c t s ru led out. This i n t e r a c t i n g w ith p h o to p e rio d can n o t be "p h o to p erio d " e f f e c t d id no t superced e the n a t u r a l v a r i a t i o n i n l e a f d r o p among f a m i l i e s u n l e s s t h e r e was an a p p r o x i m a t e 3 . 8 ° (425 km) latitu d in al b e t w e e n f a m i l y o r i g i n an d p l a n t i n g s i t e . d ifferen ce P a u l e y an d P e r r y (1954) a l s o fo u n d a s i m i l a r e f f e c t to be p r e s e n t in P o p u 1 us t r i c h o c a r p a a n d P. d e l t o i d e s . co rrelatio n s (r = -.7 1 The y r e p o r t e d to -.89) betw een sig n ifican t latitu d e c l o n e and d a t e o f h e i g h t c e s s a t i o n a t W e s t o n , Hence, of the M assachusetts. d i s c r e t i o n s h o u l d b e u s e d when m o v i n g t r e m b l i n g a s p e n f a m i l i e s m o r e t h a n 325 km ( 3 ° l a t . ) south of s ta n d b ecau se grow th c e s s a t i o n w i l l Leaf f l u s h , l e a f drop, th eir n ativ e occur e a r l i e r . an d l e a f a r e a d u r a t i o n w e r e s i g n i f i c a n t l y c o r r e l a t e d w ith l a t i t u d e of th e p a r e n ts of trem bling how ever, aspen fam ilies (Table 3.3). In b i g t o o t h l e a f d r o p was t h e o n l y p h e n o l o g i c a l s i g n i f i c a n t l y c o r r e l a t e d w ith th e l a t i t u d i n a l parents. These c o r r e l a t i o n s p h o t o p e r i o d on l e a f suggest the senescence e f f e c t o f t e m p e r a t u r e on l e a f x height) co rrelated t r a i t t h a t was o r i g i n of th e im portance of i n b o t h s p e c i e s and t h e flu sh in g At t h e E a s t L a n s i n g p l a n t a t i o n , sig n ific a n tly aspen, in tr e m b l i n g aspen. early l e a f f l u s h i n g was w ith grow th p e rfo rm a n c e (d ia m e te r* of b ig to o th aspen but not tre m b lin g aspen. B ig to o th f a m i l i e s t h a t f lu s h e d c l o s e r to th e a v e ra g e d a te of t h e l a s t s p r i n g f r o s t (May 7 t h ) later-flu sh in g bigtooth w orst b ig to o th fa m ilie s grew s l i g h t l y fam ilies. b etter than The t h r e e b e s t an d t h r e e f l u s h e d an a v e r a g e o f 10 an d 14 d a y s 61 a f t e r May 7 t h , n a tu ra lly resp ectiv ely . flu sh es e a r lie r t h a n b i g t o o t h a s p e n , m o s t (89%) o f th e tre m b lin g aspen f a m ilie s b ig to o th fam ily flu sh e d . S ince tre m b lin g aspen le a fe d out b efo re the f i r s t The e a r l i e s t f l u s h i n g t r e m b l i n g a s p e n f a m i l i e s f l u s h e d two d a y s b e f o r e May 7 t h , and a l l t r e m b l i n g a s p e n f a m i l i e s h a d f l u s h e d b e f o r e May 2 1 s t , the d a t e t h a t f r o s t i s l i k e l y t o o c c u r o n c e e v e r y 10 y e a r s . Barnes (1969) sp ecies, late hypothesized t h a t when c o m p a r i n g t h e two f l u s h i n g b y b i g t o o t h may b e a f i t n e s s a d v a n t a g e o v e r t r e m b l i n g a s p e n on a g i v e n s i t e . t h i s t h e o r y c o u l d n o t be t e s t e d However, in th e tw o - y e a r - o ld p la n ta tio n s because i n s u f f i c i e n t tim e had e l a p s e d f o r c lim a tic co nd itions (early T a b l e 3.3. fro sts) to a f f e c t tree grow th. C o r r e la tio n s of th r e e p h e n o lo g ic a l t r a i t s of h a l f s i b , f u l l - s i b , an d c o m b i n e d t r e m b l i n g and b i g t o o t h aspen f a m ilie s w ith th e l a t i t u d i n a l o r ig in of t h e i r p aren ts. S pecies Fam ily Number o f F am ilies Leaf F lush Leaf D rop L eaf Area D uration -------r ----P .trem u lo id es Do. Do. H alf-sib F u ll-sib T otal 32 41 73 -.32** -.1 4 -.21** -.43** -.2 6 * -.33** -.2 6 * -.1 8 -.22** P .g ra n d id e n ta ta Do. Do. H alf-sib F u ll-sib T otal 13 21 34 .06 -.0 2 .01 -.4 2 * -.40** -.40** -.2 0 -.2 5 -.2 4 * / * * S i g n i f i c a n t a t t h e 5 and 1 p e r c e n t l e v e l s , resp ectiv ely . 62 In g e n e r a l, aspen f a m i l i e s a t th e E a st Lansing s i t e t h a t f l u s h e d e a r l y and d ro p p e d l e a v e s all p lan tatio n s clin e 3.4. (T a b le 3.4). late grew b e t t e r a t T h e r e was a n o r t h in t h e s i z e o f th e c o r r e l a t i o n to south co efficien ts in T ab le N o r t h e r n p l a n t a t i o n s had h i g h e r c o r r e l a t i o n s , b e c a u s e th e s h o r t e r grow ing s e a so n s a t th ese s i t e s would fa v o r f a m i l i e s w ith p h e n o lo g ie s t h a t c o u ld use a l l grow ing T able of the season. 3.4. S ite p o ssib ly C o r r e l a t i o n s o f t w o - y e a r g r o w t h p e r f o r m a n c e o f 179 b i g t o o t h , t r e m b l i n g , and h y b r i d a s p e n f a m i l i e s a t each p l a n t a t i o n w ith t h e i r r e s p e c t i v e p h e n o lo g ic a l t r a i t s re c o rd e d a t th e E a s t Lansing p l a n t a t i o n . F ro st-free P eriod S pecies L a titu d e (Days) Leaf Flush Leaf F all L e af Area D uration _____ r a / . A ll A ll A ll A ll 4 6 . 3°N 4 3 . 5°N 4 2 . 7°N 4 2 . 0°N 100 126 151 158 .45 .45 .48 .18 .55 .53 .53 .23 .61 • in in . I Com bine d -.5 0 -.4 3 -.3 6 -.2 7 o in C h a th a m Six Lakes E .L ansing D ecatur -------- r W . E .L ansing P .g ra n d id e n ta ta P .trem u lo id es P .X sm ithi i -.36** -.1 3 -.2 1 * .25* .45** .25** .43** .44** .35** A l l c o e f f i c i e n t s w e r e s i g n i f i c a n t a t t h e 1% l e v e l . —/ C o efficien ts sig n ifican t at t h e 5% (*) o r 1% (**) lev el. 63 The r e s u l t s v alid f r o m t w o - y e a r g r o w t h d a t a may n o t b e o v e r th e lo n g term b e c a u s e p e r i o d i c are d etrim en tal F u rth erm o re, to e a r l y flu sh in g late fam ilies spring f r o s ts ( S t r a i n 1966). t h e s e f a m i l i e s may h a v e r a n k e d d i f f e r e n t l y if th e y had b een s c o re d f o r p h e n o lo g y a t th e o th e r t h r e e p lan tatio n s. However, i f p h o t o p e r i o d an d t e m p e r a t u r e a r e th e en v iro n m en tal s tim u li phenology ra n k in g s a t fo r aspen phenology, then th e t h e E a s t L a n s i n g s i t e may b e a p p l i c a b l e to th e p h e n o lo g ic a l at the o th e r r e s p o n s e s t h a t w o u ld be found site s. M orphological C h a ra c te rs Autumn l e a f c o l o r w i t h i n an d b e t w e e n s p e c i e s and f a m i l i e s a t th e E a st Lansing s i t e orange to red. Barnes (1 96 9) varied reported from y e l l o w to t h a t a ran g e of a u t u m n c o l o r s e x i s t e d b e t w e e n a s p e n c l o n e s an d s p e c i e s M ichigan. S ig n ifican t d ifferen ces b e t w e e n t h e s p e c i e s an d h y b r i d s . trem bling aspen f a m il i e s y e l l o w w i t h some r e d s . in t h i s ( T a b l e 3.5 ) w e r e f o u n d The a u t u m n c o l o r s o f m o s t t e s t were p r e d o m i n a n t l y Autumn c o l o r a t i o n o f b i g t o o t h f a m i l i e s was m o s t l y y e l l o w - o r a n g e o r o r a n g e - r e d . X s m ith ii f a m i l i e s were l a r g e l y y e llo w . th e h y b rid trem bling P. The c o l o r a t i o n o f f a m i l i e s c o rre sp o n d e d c l o s e l y to t h a t of t h e i r aspen p a re n t. The n a r r o w - s e n s e h e r i t a b i l i t y variance) in for (a d d itiv e genetic l e a f c o l o r a t i o n as c a l c u l a t e d m a t i n g d e s i g n d a t a was 0 . 3 4 . from t h e n e s t e d The m a l e p a r e n t variance c o m p o n e n t was s i g n i f i c a n t a t t h e 10% l e v e l o f p r o b a b i l i t y T a b l e 3.5. Mean r a n k s fro m F r i e d m a n ’ s two-way c l a s s i f i c a t i o n t e s t f o r s i x m o r p h o l o g i ­ c a l and p h y s i o l o g i c a l c h a r a c t e r s m e a s u r e d i n 206 a s p e n and h y b r i d a s p e n f a m i l i e s a t th e E ast Lansing p l a n t a t i o n . M orphological C h a ra c te rs Taxa F all C olor Number o f Branches Bud D ivergence P h y siological C haracters Bud Pubescence Shoot Dieback Basal Sprout -Mean Ranks^ , 2 ______________ P .g ran d id en tata 6.0 1.0 5.2 5.0 2.3 2.4 P .g ran d id en tata X P .trem ulo id es P .trem u lo id es X P .grandidentata 3.0 2.5 3.5 2.8 4.2 5.8 3.0 3.5 2.5 2.2 5.3 4.5 P .trem uloides 2.3 5.2 1.0 1.0 1.7 2.3 (P .X rouleauiana) X P .trem u lo id es (P.X rouleauiana) X P .g ran d id en tata 2.0 5.7 3.0 4.0 4.4 4.2 4.7 3.2 5.8 6.0 3.3 1.8 C h i2 Value 20** 25** 27** 30** 16** 21** 1 Each mean r a n k i s t h e r a n k i n g o f n o n - p a r a m e t r i c d a t a f o r one t r a i t o f one t a x o n w i t h r e s p e c t to th e d a ta o f th e o th e r taxa. T h e s e r a n k i n g s a r e a v e r a g e d a c r o s s t h e number o f r e p l i c a t e s i n t h e t e s t (= mean r a n k s ) , i e . , The mean r a n k o f 6.0 f o r f a l l c o l o r i n P. g r a n d i d e n t a t a s i g n i f i e s t h a t t h i s s p e c i e s a l w a y s r a n k e d s i x t h i n t h e f a l l c o l o r data of every r e p l ic a t e . See M a t e r i a l s and M eth ods s e c t i o n f o r e x p l a n a t i o n o f t h e s c o r i n g o f e a c h c h a r a c t e r . 65 and t h e f e m a l e - w i t h i n - m a l e v a r i a n c e c o m p o n e n t was h i g h l y sig n ifican t (P<.01). have n o n -a d d itiv e g en etic v ariance x anthophylls scores for Autumn c o l o r a t i o n (dom inant e f f e c t s ) to as w e l l as a d d i t i v e f o r g e n e s t h a t p r o d u c e c a r o t e n e s an d ( y e l l o w - o r a n g e p i g m e n t s ) b e c a u s e t h e mean c o l o r f a m i l i e s w i t h t r e m b l i n g a s p e n p a r e n t a g e w e r e 2.3 (trem bling X b ig to o th ), poplar in asp en a p p e a r s 2.3 hybrid X tre m b lin g ) , co n trast, big to o th in c o l o r . A lleles fam ilies (the recip ro cal), an d 2.2 2.2 (w hite (trem b ling ). In a v e r a g e d 3.3, which i s orange-red f o r a n th o c y a n in p ig m en ts m ight be e i t h e r a t t h e same l o c i a s t h e c a r o t e n o i d a l l e l e s b u t a r e r e c e s s i v e to th ese a l l e l e s affected or th e anth o cy an in genes a re e p i s t a t i c a l l y by t h e c a r o t e n o i d genes. The number o f p r i m a r y b r a n c h e s p e r t r e e grow ing s e a s o n in th e sig n ific a n tly betw een T y p ically , fie ld the after (two y e a r s f r o m s e e d ) species an d h y b r i d s £ . Xs m i t h i i f a m i l i e s were i n t e r m e d i a t e , b u t t h e b r a n c h number o f t h e m a t e r n a l p a r e n t . number i n P. Xr o u l e a u i a n a b a c k c r o s s e s (T a b le 3.5). B ranching of tended to f a v o r A lso , branch favored th e aspen A d d i t i v e an d m a t e r n a l e f f e c t s may b e i n v o l v e d b u d r e l e a s e and t h e s u b s e q u e n t l a t e r a l aspen d u rin g the f i r s t grow ing s e a s o n in th e f i e l d . sig n ific a n tly co rrelated grow ing s e a s o n . in In ( r = .46) w e re w i t h b r a n c h number a f t e r T herefore, in branch form ation a d d i t i o n , b o t h h e i g h t ( r = .29) and d i a m e t e r fie ld d iffered t r e m b l i n g a s p e n p r o d u c e d f i v e o r m o re b r a n c h e s , w h e r e a s b i g t o o t h a s p e n p r o d u c e d few o r n o n e . p arent. one the f i r s t b r a n c h nu m b er i n y o u n g 66 t r e e s may b e d e t e r m i n e d by b o t h t h e s p e c i e s g e n o t y p e and t h e p h y sical s i z e a t t a i n e d by t h e g e n o t y p e (genotype x en v iro n m e n t). S i g n i f i c a n t d i f f e r e n c e s b e tw e e n s p e c i e s and h y b r i d s were found f o r bud o r i e n t a t i o n (Table 3.5). Bud d i v e r g e n c e was e s s e n t i a l l y a b s e n t i n t r e m b l i n g a s p e n an d u b i q u i t o u s b ig to o th aspen, a l t h o u g h t h e r e were e x c e p t i o n s . The v a r i a t i o n b e t w e e n an d w i t h i n t h e P. X s m i t h i i f a m i l i e s bud o r i e n t a t i o n was v e r y l a r g e . in for The mean o f t h e h y b r i d f a m i l i e s was a p p r o x i m a t e l y i n t e r m e d i a t e t o t h e p a r e n t s p e c i e s , b u t t h e bud o r i e n t a t i o n w i t h i n a h y b r i d m o re o f t e n o rien tatio n lik e th a t of the m atern al p a re n t. f a m i l y was Bud i n t h e P. X r o u l e a u i a n a b a c k c r o s s e s was i n f l u e n c e d by t h e a s p e n p a r e n t , b u t g e n e r a l l y r e s e m b l e d b i g t o o t h a s p e n b e c a u s e P. a l b a h a s d i v e r g e n t b u d s . Non­ a d d i t i v e g e n e t i c e f f e c t s p r o b a b l y were i n v o l v e d b e c a u s e of the u n p re d ic ta b le s e g re g a tio n of t h i s tra it in th e h y brid fam ilies. S i g n i f i c a n t d i f f e r e n c e s b e t w e e n s p e c i e s an d h y b r i d s w e r e f o u n d f o r bud s c a l e p u b e s c e n c e (Table 3.5). N o ticeab le p u b e s c e n c e on t h e b u d s c a l e s was a b s e n t i n t r e m b l i n g a s p e n , b u t was common i n b i g t o o t h f a m i l i e s ha d l i t t l e aspen. M o s t P. Xs m i t h i i bud s c a l e p u b e s c e n c e . Hybrid f a m i l i e s w i t h b i g t o o t h a s p e n a s t h e m a t e r n a l p a r e n t h ad s l i g h t l y m o r e pubescence than th e r e c i p r o c a l h ybrid. d e n s e t o m e n tu m on i t s bud s c a l e s , S i n c e P. a l b a h a s a t h e P. Xr o u l e a u i a n a b a c k c r o s s e s w i t h b i g t o o t h a s p e n h a d m ore p u b e s c e n c e t h a n b i g t o o t h f a m i l i e s , an d w i t h tre m b lin g aspen as th e b ack cro ss 67 parent, slig h tly The g r a d u a l l e s s pubescence than b ig to o th clin e fam ilies. f r o m P. t r e m u l o i d e s t o P. X r o u l e a u i a n a in t h e a m o u n t o f bud s c a l e p u b e s c e n c e s u g g e s t e d a d d i t i v e e f f e c t s w ere i m p o r t a n t . P h y sio lo g ic a l A bnorm alities S ig n ific a n t d iffe re n c e s existed h y b rid s b e t w e e n t h e s p e c i e s and i n t h e o c c u r r e n c e o f s t e m d i e b a c k an d bu d a b o r t i o n (T a b le 3.5). trem bling O n l y a few i n d i v i d u a l s f r o m t h e b i g t o o t h and f a m i l i e s h a d some t y p e o f s h o o t d i e b a c k . However, t h i s d i e b a c k was n o t uncommon i n a num be r o f h y b r i d fam ilies. B o t h P. Xs m i t h i i c r o s s e s an d t h e P. X r o u l e a u i a n a b a c k c r o s s e s had i n d i v i d u a l s w ith t h e d i s o r d e r . The h y b r i d d y s g e n e s i s was p r o b a b l y t h e d i e b a c k s y n d r o m e t h a t H e i m b u r g e r (1940) found in £ . X s m ith ii d u r in g h i s e a r l y h y b r i d i z a t i o n stu d ies. S ig n ifican t d ifferen ces in th e fre q u e n c y of r o o t c o l l a r s p r o u t i n g w e r e p r e s e n t b e t w e e n t h e s p e c i e s and h y b r i d s (T a b le 3 .5 ). Many P . Xs m i t h i i a n d (P . X r o u l e a u i a n a ) X P. t r e m u l o i d e s f a m i l i e s had f r o m o n e t o t e n s p r o u t s e m e r g i n g from t h e r o o t c o l l a r D espite t h i s d u r in g th e second growing s e a s o n . abundant sp ro u tin g , actively-grow ing term inal the tr e e s m aintained lead ers. The g e n e t i c r e g u l a t i o n o f e n d o g e n o u s h o r m o n e s i n t h e s e h y b r i d s may h a v e m alfu n ctio n ed , thereby, releasin g b a s a l buds from i n h i b i t o r developed b a s a l grew l e s s sp routing t h e a d v e n t i t i o u s and hormones. H ybrid f a m i l i e s that in th e second grow ing s e a so n o f t e n in h e ig h t than h y b rid f a m ilie s w ithout s p ro u ts. 68 The y o u n g s u c c u l e n t s h o o t t i p s o f t h e s e s p r o u t s w e r e s t r o n g sin k s f o r p h o t o s y n t h a t e p r o d u c e d by t h e tree. These s p r o u t s e i t h e r b e c a m e o v e r t o p p e d b y t h e c a n o p y an d d i e d o r t h e y continued t o grow and d i v e r t p h o t o s y n t h a t e fro m t h e m a i n stem . D iseases, In sects, and Deer An unnamed v i r u s l e a f s p o t d e s c r i b e d by Boyer was a s e v e r e p r o b l e m f o r a few P. Xs m i t h i i h y b r i d f a m i l i e s had t h i s d i s e a s e tre m b lin g aspen f a m il i e s . (1962) fam ilies. More t h a n d i d b i g t o o t h an d Boyer a l s o found t h i s to be t r u e w i t h h y b r i d a s p e n t h a t he had i n o c u l a t e d w ith t h e v i r u s . H o w e v e r , t h e r e w e r e no s i g n i f i c a n t d i f f e r e n c e s b e t w e e n sp ecies an d h y b r i d s in in cid en ce of t h i s d is e a s e . A s e r i o u s f u n g a l s h o o t p e s t was V e n t u r i a t r e m u l a e . h a s b e e n r e p o r t e d b y D an ce (1961) t o a t t a c k o n l y t h e y o ung s h o o t s o f b o t h b i g t o o t h an d t r e m b l i n g a s p e n . t h a t the It D an ce o b s e r v e d tim e span o f s u s c e p t i b i l i t y to V e n tu r ia tr e m u la e is about s ix weeks, b e g in n in g in e a r l y May. He r e p o r t e d th at t r e m b l i n g a s p e n i s more s e r i o u s l y i n j u r e d t h a n b i g t o o t h aspen because b ig to o th later; hence, in itiates t h e tim e d u r i n g which r e i n f e c t i o n b ig to o th d u rin g th e s u s c e p tib le In t h i s (T able 3.6) an d h y b r i d s h o o t g r o w t h two w e e k s stu d y , in period t h e r e were a l s o in fe ctio n rates is sh o rter. betw een t r e m b l i n g , b igtooth, aspen which s u p p o r t e d D an ce's f i n d i n g s . least su scep tib le. in sig n ific a n t differen ces T r e m b l i n g a s p e n was t h e m o s t s u s c e p t i b l e , was t h e can o c c u r whereas b ig to o th The h y b r i d s w e r e i n t e r m e d i a t e , 69 a lth o u g h h y b rid s w ith a tre m b lin g more s u s c e p t i b l e a s p e n p a r e n t w e r e much than th e w hite p o p la r x b ig to o th aspen h y b rid . Genes w ith a d d i t i v e e f f e c t s , c o n t r i b u t e d by one s p e c i e s , which were l a r g e l y P. t r e m u l o i d e s , a p p e a r in flu e n c e d aspen s u s c e p t i b i l i t y to have to V e n tu ria tr e m u la e . o f t h e s e g e n e s w e r e p r o b a b l y t h e same o n e s o r c l o s e l y to those th a t c o n t r o ll e d tim e of leaf Some linked f l u s h , s i n c e D ance's w ork and t h e l e a f f l u s h d a t a i n T a b l e 3.1 s u p p o r t t h i s hy pothesis. R e s i s t a n c e was f o u n d i n some b i g t o o t h w hereas o n ly d i f f e r e n c e s fam ilies, in t h e d e g r e e o f s u s c e p t i b i l i t y to V e n t u r i a w e r e f o u n d among t r e m b l i n g f a m i l i e s . T a b l e 3.6 . S u s c e p t i b i l i t y to V e n t u r i a tr e m u la e in p e r c e n t o f t h e p l a n t a t i o n mean f o r e a c h s p e c i e s an d h y b r id a t t h e S ix Lakes p l a n t a t i o n . Taxa S u sc ep tib ility in % of P l a n t a t i o n Mean T otal Number of P lo ts P ercentage of P lo ts Infected P. g r a n d id e n ta ta 31 72 8 (P .X rouleauiana) X P .g ran d id en tata 35 32 9 (P .X rouleauiana) X P .trem uloides 88 51 22 P .grandidentata X P .trem uloides 98 102 25 P . trem uloides X P .g ran d id en tata 93 97 23 120 315 30 P . trem uloides 70 The m o s t d e s t r u c t i v e p o p lar-g all b eetle, reported progeny t e s t s , grow th, t o b e a common a s p e n p e s t are h ig h ly su sc e p tib le fungal decay, to a tta c k . in fam ilies h eav ily -in fested . from a l l T w o -y ear-o ld on t h e m a i n s t e m . secondary fungal S tunted and H y p o x y lo n c a n k e r s s e c o n d a r y e f f e c t s o f S a p e rd a damage. Six Lakes s i t e , At t h e s p e c i e s an d h y b r i d s w e r e t r e e s h a d a s many a s s i x Damage f r o m s t e m b r e a k a g e an d p a t h o g e n s was m o s t p r o n o u n c e d on t h e d r y , sandy Six Lakes s i t e b etter (1972) This b o re r has been Th ey f o u n d t h a t o p e n s t a n d s , s u c h a s y o u n g stem b r e a k a g e , were t y p i c a l g alls Saperda in o rn a ta . b y Nord j e t a l . t h e Lake S t a t e s . i n s e c t i n t h e p r o g e n y t e s t was t h e p lan tatio n b e c a u s e t r e e v i g o r was lo w . site s (ie ., D ecatur), enough so t h a t stem damage from l a r v a l On t h e t r e e s were v ig o r o u s b o r i n g was m i n i m i z e d by p r o d u c t io n of s u f f i c i e n t xylem to p r e v e n t stem b re a k a g e . T h e r e w e r e no s i g n i f i c a n t d i f f e r e n c e s b e t w e e n s p e c i e s and h y b r i d s in s u s c e p t i b i l i t y (P. Xr o u l e a u i a n a ) X P. many g a l l s per tre e to Saperda a tta c k . However, tre m u lo id e s h y b rid s averaged tw ice as a s d i d P. g r a n d i d e n t a t a . A pparently i t was no c o i n c i d e n c e t h a t t h e f o r m e r t a x o n a l s o h a d t h e f a s t e s t g r o w i n g f a m i l i e s and t h e ones. By a g e t w o , fast-grow ing latter t r e e s had a t t a i n e d mm d i a m e t e r r a n g e t h a t G r i m b l e e t aJL. the p re fe rre d H eight stem s i z e ( r = . 28) th e s l o w e s t growing (1969) reported t o be fo r o v ip o s itin g Saperda b e e t l e s . and d i a m e t e r ( r = .3 2) w e r e s i g n i f i c a n t l y c o r r e l a t e d w i t h t h e number o f S a p e r d a g a l l s does not n e c e s s a r ily t h e 8-14 in fer p e r stem . t h a t v i g o r o u s t r e e s a r e m ore This 71 g e n e tic a lly s u s c e p tib le but instead s u p p o r t m o re l a r v a e suffered sm aller (g alls). sh ow s t h a t V igorous larg er trees t r e e s , how ever, l e s s stem b r e a k a g e from l a r v a l boring than d id trees. The a p p a r e n t l a c k o f s p e c i e s r e s i s t a n c e t h e s i g n i f i c a n t damage t h a t t h e p lan tatio n s g en etic l a r v a e c a u s e to young a s p e n s h o u l d b e c o n s i d e r e d when s e l e c t i n g tests of aspen taxa. s h o u ld be a v o id e d spraying t o S a p e r d a and if th is and s a n i t a t i o n sites for Poor to a v e r a g e asp en s i t e s in se c t is p resen t u n less a program A nother sh o o t i n s e c t , is t o be in stitu ted . t h e w i l l o w s h o o t s a w f l y (J a n u s a b b r e v i a t u s ) , was a s e r i o u s p e s t i n t h e n u r s e r y and a l e s s e r p ro b lem in th e E a st L ansing p l a n t a t i o n . The b i o l o g y o f t h i s in sect i n t h e L a k e s S t a t e s h a s b e e n d e s c r i b e d b y Osgood (1 96 2) and Gr aham e t £1^. (1963). L a n s i n g p l a n t a t i o n was g r e a t e s t and d e c r e a s e d the fo llo w in g root c o lla r damaged. the East in th e f i r s t grow ing se a so n two y e a r s . g r o w i n g s e a s o n 2. 5 p e r c e n t o f a l l a ll S h o o t dam ag e i n In th e second term in al s h o o t s a n d 60% o f s p r o u t s w e r e g i r d l e d an d e i t h e r k i l l e d or T h e r e was no p r e f e r e n c e f o r o n e t a x o n b y t h e w illo w shoot saw fly. H o w e v e r , P. X s m i t h i i f a m i l i e s suffered t h e m o s t w i l l o w s h o o t s a w f l y dam ag e b e c a u s e t h e a b n o r m a l root c o lla r s p ro u tin g of th e se h y b rid s p ro v id ed w ith s u c c u le n t s p ro u ts for o v ip o sitin g . which p ro d u ced numerous r o o t c o l l a r chosen for f u t u r e b r e e d i n g work. the s a w f l i e s These f a m i l i e s , sprouts, s h o u l d n o t be 72 The p o p l a r tentm aker i n s e c t problem . (C l o s t e r a The l a r v a e o f t h i s m o t h d e f o l i a t e d p e rc e n t of the tr e e s at the D ecatur p l a n t a t i o n E n t i r e cottonw ood p l a n t a t i o n s com pletely d e f o lia te d notodontid i n c l u s a ) was y e t a n o t h e r i n 1 9 83. in M i s s i s s i p p i h a v e been in as l i t t l e ( S t e i n and O l i v e r i a 35 as t h r e e days by t h i s 1979). M o r t a l i t y and g r o w t h l o s s h a v e been e c o n o m i c a l l y s i g n i f i c a n t in t h e s e cottonw ood p lan tatio n s. The p o p l a r t e n t m a k e r h a s b e e n r e l a t i v e l y unknown i n M i c h i g a n b u t r e c e n t l y h a s b e e n r e p o r t e d B errien, Cass, and S t . p a r t of the s t a t e . resista n ce Joseph c o u n tie s in th e s o u th w e s te r n T h e r e w e r e no d i f f e r e n c e s t o t h e t e n t m a k e r among t h e a s p e n F a m ilie s w ith e i t h e r in in g e n e t i c taxa a t D ecatur. tre m b lin g or b ig to o th aspen as the m a t e r n a l p a r e n t h a d 34 a n d 35 p e r c e n t d e f o l i a t i o n , resp ectiv ely . If th is i n s e c t becomes a p r o b le m in s o u th w e ste rn M ichigan, ch em ical c o n t r o l has been p ro v en to be e f f e c t i v e (C oster In a d d i t i o n to 1973). i n s e c t s an d d i s e a s e s , common p r o b l e m i n t h e p l a n t a t i o n s . B r o w s i n g and f a l l r u b b i n g b y m a l e d e e r dam ag ed o r k i l l e d many t r e e s . tree d e e r dam a g e was a t h e main s te m s o f H o w e v e r , t h e c o r r e l a t i o n b e t w e e n b r o w s i n g and h e i g h t was v e r y sm all ( r = .0 4) and i n s i g n i f i c a n t . P r e f e r e n c e f o r a p a r t i c u l a r a s p e n t a x o n was n o t e v i d e n t th is study. The i m p o r t a n c e o f d e e r b r o w s i n g d e p e n d s on t r e e v i g o r . d e e r brow sing a f t e r in in a p l a n t a t i o n F ast-grow ing t r e e s u s u a l l y escape two o r t h r e e y e a r s . Slow -grow ing t r e e s o r t r e e s p l a n t e d on p o o r s i t e s may b e s t u n t e d in d efin itely 73 and bec om e i n f e c t e d b y s e c o n d a r y p a t h o g e n s . Because d eer r e p e l l e n t s h a v e n o t g i v e n p r o m is in g r e s u l t s th u s f a r in aspen p l a n t i n g s (R eighard, p e r s o n a l o b servation), p la n tin g s u p e r i o r g e n o t y p e s and a v o i d i n g p o o r s i t e s w i l l lessen i m p a c t o f d e e r on a s p e n e s t a b l i s h m e n t an d g r o w t h . the 74 LITERATURE CITED A h l g r e n , C.E. 1 957. P henological o b se rv a tio n s of nineteen n ativ e tre e sp e c ie s. E cology 3 8 :6 2 2 -6 2 8 . B a r n e s , B.V. 1 9 69. N a t u r a l v a r i a t i o n and d e l i n e a t i o n o f c l o n e s o f P o p u l u s t r e m u l o i d e s a n d P. g r a n d i d e n t a t a i n n o r t h e r n Lower M i c h i g a n . sTTvae G e n e t i c a 1 8 : 1 3 0 - 1 4 2 . B o y e r , M.G. 1 9 62. n a tiv e aspen. A l e a f - s p o t t i n g d is e a s e of h y brid Can. J . B o t. 4 0 :1 2 3 7 - 1 2 4 2 . an d C o s t e r , J .E . 1973. System ic i n s e c t i c i d e s e f f e c t i v e a g a in s t p o p l a r t e n t m a k e r in co tto n w o o d p l a n t a t i o n s . Tree P l a n t e r s ' N otes 2 4 ( l ) : 3 3 - 3 4 . D a n c e , B.W. Can. J . 1961. Spore d i s p e r s a l B ot. 39:1429-1435. in P o l l a c c i a r a d i o s a . D o m a n s k i , R. and T.T. K o z l o w s k i . 1 968. V a r i a t i o n s in k i n e t i n - l i k e a c t i v i t y i n b u d s o f B e t u l a an d P o p u l u s d u r i n g r e l e a s e from dorm a n cy . Can. J . B o t. 4 6 :3 9 7 - 4 0 3 . G r a h a m , S . A . , R.P . H a r r i s o n , J r . , a n d C.E. W e s t e l l , J r . 1963. A spens: Phoenix T re e s o f th e G re a t Lakes R egion. Univ. o f M i c h . P r e s s , Ann A r b o r . 272 p p . G r i m b l e , D.G ., J . C . N o r d , a n d F .B . K n i g h t . 1969. O v i p o s i t i o n c h a r a c t e r i s t i c s and e a r l y l a r v a l m o r t a l i t y o f S a p e r d a i n o r n a t a and O b erea s c h a u m i i i n M ic h ig a n a s p e n . Ann. E n t o m o l . S o c . Am. 6 3 : 3 0 8 - 3 1 5 . H e i m b u r g e r , C. 1940. R e p o r t on p o p l a r h y b r i d i z a t i o n 1937 a n d 1 9 3 8 . F o re s try C h ro n icle 16:149-160. H e w e t t , E.W. and P.F. W a r e i n g . 1973. ro b u sta : changes d uring c h i l l i n g P la n t. 28:393-399. II in C y to k in in s in P o p u lu s X and b u d b u r s t . P hysiol. H u l l , C.H. a n d N.H. N i e . 1981. SPSS U p d a t e 7 - 9 : New P r o c e d u r e s an d F a c i l i t i e s f o r R e l e a s e 7 - 9 . M cG raw -H ill Book C o . , New Y o r k . 402 p p . I s e b r a n d s , J.G. an d N.D. N e l s o n . 1 9 82. Crown a r c h i t e c t u r e o f s h o r t - r o t a t i o n , i n t e n s i v e l y c u l t u r e d P o p u lu s I I . 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P l a n t D i s . 6 7 : 1 8 7 - 8 9 . R e i g h a r d , G.L. 1984. P h y s io lo g ic a l g e n e tic s s tu d ie s of P o p u l u s g r a n d i d e n t a t a , P. t r e m u l o i d e s , and t h e i r h y b r i d , P . Xs m i t h i i . P h . D . T h e s i s . M i c h i g a n S t a t e U n i v . 110 p p . S a k a i , A. and C . J . W e i s e r . 1 9 73. Freezing r e s is ta n c e of t r e e s in N orth Am erica w ith r e f e r e n c e to t r e e r e g i o n s . Ecology 5 4 ( 1 ) :1 1 8 - 1 2 6 . S t e e l , R.G.D. a n d J . H . T o r r i e . Procedures of S t a t i s t i c s . York. 481 p p . 1960. P r i n c i p l e s and M c G r a w - H i l l Book Co., New 76 S t e i n , C.R. an d F.L. O l i v e r i a . 1979. S ta tu s of p o p la r te n tm a k e r in th e low er M i s s i s s i p p i R iv er D e l t a . U .S.D .A . F o r . S e r v . F o r e s t I n s e c t & D i s e a s e R e p o r t No. 7 9 - 2 - 7 . S t r a i n , B.R. 1 966. The e f f e c t o f a l a t e s p r i n g f r o s t on t h e r a d i a l grow th o f v a r i a n t quaking asp en b i o t y p e s . Forest S cience 12(3):334-337. W eir, R .J. 1983 . Economics o f T ree Im provem ent. IN / Tw entyS e v e n t h A n n u a l R e p o r t o f t h e N.C. S t a t e U n i v e r s i t y I n d u s t r y C o o p e r a t i v e T ree Im provem ent Program , p p .36-41. W r i g h t , J.W. 1 9 76. I n tr o d u c tio n to F o r e s t G e n e tic s. A c a d e m i c P r e s s , New Y o r k . 463 p p . Z s u f f a , L. 1 9 73. A summary r e v i e w o f i n t e r s p e c i f i c b r e e d i n g in th e genus P o p u lu s. IN/ P ro c. o f th e 14th m e e tin g of t h e C an a d ia n T ree Im provem ent Assoc. D.P. F o w l e r and C.W. Y eatm an ( E d i t o r s ) . F r e d e r i c t o n , N.B. p p . 1 0 7 - 1 2 3 . CHAPTER 4 C om parative P h y s i o l o g i c a l S tu d ie s o f P h o to s y n th e s is , Shoot and Root D e v e lo p m e n t, an d D ry M a t t e r P a r t i t i o n i n g P o p u l u s g r a n d i d e n t a t a , P, in t r e m u l o i d e s , an d P . X s m i t h i i (To b e S u b m i t t e d t o F o r e s t S c i e n c e ) ABSTRACT P h o t o s y n t h e s i s , s h o o t a n d r o o t d e v e l o p m e n t , an d d r y m atter p a r titio n in g were s t u d i e d in P o p u lu s g r a n d i d e n t a t a , P. t r e m u l o i d e s , an d t h e i r h y b r i d g as-ex ch an g e system , P. X s m i t h i i u s i n g h y d roponics, an d a n u r s e r y . no s i g n i f i c a n t d i f f e r e n c e s among t a x a and d a r k r e s p i r a t i o n rates. a closed There were in n e t p h o t o s y n t h e s i s Whole p l a n t p h o t o s y n t h e s i s and r e s p i r a t i o n were s i g n i f i c a n t l y c o r r e l a t e d w ith l e a f d r y w eight, shoot dry w e ig h t, high n et p h o to sy n th e tic and l e a f a r e a . S e e d lin g s w ith r a t e s and l a r g e l e a f a r e a s a s s i m i ­ l a t e d t h e m o st d r y m a t t e r , b u t d i d n o t n e c e s s a r i l y grow t h e talle st. P. t r e m u l o i d e s p r o d u c e d s i g n i f i c a n t l y m o r e p r i m a r y ro o ts less and secondary X sm ith ii produced than e i t h e r species ro o ts t h a n P. g r a n d i d e n t a t a . P. s l i g h t l y m o r e p r i m a r y and s e c o n d a r y r o o t s parent sp ecies. R ates o f r o o t grow th in b o th an d t h e h y b r i d w e r e s i m i l a r after f i v e weeks. J?. t r e m u l o i d e s h a d a 50% s m a l l e r r o o t t o s t e m r a t i o t h a n P. gran d id en tata. p arents. H y b r i d s h ad r a t i o s sim ilar to t h e i r m a te rn a l The g a s - e x c h a n g e an d h y d r o p o n i c s t u d i e s w e r e n o t e f f e c t i v e m ethods f o r p r e d i c t i n g a s p e n s grown u n d e r fie ld dry m atter pro d u ctio n of cond itio n s in t h e n u r s e r y . 78 INTRODUCTION Aspens a r e f a s t- g r o w in g tem perate tr e e s p e c i e s which h av e e v o l v e d m e t a b o l i c p r o c e s s e s t h a t prom ote r a p i d j u v e n i l e grow th. Numerous s t u d i e s o f k e y p h y s i o l o g i c a l t r a i t s have b e e n c o n d u c te d in a s p e n s to e l u c i d a t e which o f t h e s e t r a i t s are r e l i a b l e stu d ies i n d i c a t o r s of grow th p o t e n t i a l . (Gatherum e t 1967, P hotosynthesis Domingo an d G o r d o n 1 9 7 4 , O k a f o and H a n o v e r 1978 ) h a v e b e e n t h e m o s t f r e q u e n t l y reported, a lth o u g h th e r e s u l t s have not p ro v id ed c o n c lu s iv e ev idence th a t n e t p h o to sy n th e sis is s i g n i f i c a n t l y c o r r e la te d w ith grow th r a t e . An i n h e r e n t p r o b l e m w i t h p h o t o s y n t h e s i s s tu d i e s has been t h a t f i e l d d u p licated c o n d itio n s c a n n o t be e a s i l y i n t h e l a b and e v e n when t h e y a r e a p p r o x i m a t e d , th e s h o r t - t e r m n a t u r e of th e s e g a s-e x c h a n g e m easurem ents p r o b a b l y do n o t a c c u r a t e l y r e p r e s e n t t h e l o n g - t e r m g a s exchange p ro cesses in a n a tu r a l environm ent. In c o n t r a s t to p h o t o s y n t h e s i s , tra its such as l e a f a r e a , p artitio n in g h elp fu l other p h y s io lo g ic a l s h o o t and r o o t g r o w t h , a n d c a r b o n ( Z a v i t k o v s k i 1 9 7 1 , O k a f o 1976) in d e f i n i n g th e grow th p o t e n t i a l h a v e b e e n m o re of aspen s p e c ie s . These p h y s i o l o g i c a l p r o c e s s e s h a v e n o t y e t been i n v e s t i g a t e d i n c o m p a r a t i v e s t u d i e s b e t w e e n a s p e n s p e c i e s an d t h e i r h yb rid s. F u r t h e r m o r e , many o f t h e s e m easured under b o th tra its l a b o r a t o r y and f i e l d have no t been cond itio n s. U n d e rsta n d in g t h e r e l a t i o n s h i p betw een p l a n t p h y s i o l o g i c a l p r o c e s s e s and d r y m a t t e r p r o d u c t i o n w i l l p ro v id e the f o r e s t g e n e t i c i s t w ith im p o rta n t in fo rm a tio n co n cern in g th e 79 f e a s i b i l i t y of using tra its in d irect sele ctio n fo r biom ass y i e l d . in p h y s i o l o g i c a l Studying th e s e tra its in aspen s p e c i e s and t h e i r h y b r i d s w i l l g i v e an i n d i c a t i o n o f how s im ila r g e n e tic a lly these processes are p a r e n t s p e c i e s and t h e r e f o r e , i n t e r - an d i n t r a s p e c i f i c biom ass aid in t h e d i f f e r e n t in th e d e v e lo p m e n t o f h y b r i d i z a t i o n program s to im prove p ro d u ctio n . The o b j e c t i v e s o f t h i s s t u d y w e r e t o i n v e s t i g a t e photo sy n th esis, p artitio n in g s h o o t and r o o t d e v e l o p m e n t , and c a r b o n i n two s y m p a t r i c b u t e c o l o g i c a l l y d i s t i n c t aspen s p e c ie s (P o p u l u s g r a n d i d e n t a t a an d P. t r e m u l o i d e s ) and t o d e t e r m i n e how t h e s e i n t e r d e p e n d e n t p h y s i o l o g i c a l p r o c e s s e s were e x p r e s s e d ad d itio n , in t h e i r h y b r i d , P. X s m i t h i i . the im portance of th e s e p ro c e ss e s r e l a t i v e p l a n t biom ass p r o d u c tio n under b o th a r t i f i c i a l In to and n a t u r a l e n v i r o n m e n t s was e v a l u a t e d . MATERIALS AND METHODS P h o t o s y n t h e s i s Study S e e d lin g s of b ig to o th aspen trem b ling aspen (P. (P o p u l u s g r a n d i d e n t a t a ) , t r e m u l o i d e s ) , an d t h e i r X s m i t h i i ) w ere grown i n d o o r s in h ybrid (P. a g r o w t h f r a m e f o r 12 w e e k s . These s e e d l i n g s r e p r e s e n t e d s e v e n f u l l - s i b fam ilies. Each s e e d l i n g w a s g r o w n i n a 6 x 6 x 27 cm p o l y c o a t e d p a p e r p l a n t b a n d t h a t had b e e n f i l l e d p a rts p eat, in serted p e rlite , w ith m edia c o n s i s t i n g an d v e r m i c u l i t e . o f 1:1:1 The b a n d s w e r e i n p l a s t i c m i l k c a s e s w i t h 25 b a n d s t o a c a s e . s e e d l o t was sown p e r c a s e . The r o o t m e d i a was w a t e r e d One 80 w h en ev er t h e s u r f a c e became d r y , fe rtiliz e d and t h e s e e d l i n g s w e r e o n c e a week w i t h P e t e r s S o i l T e s t F e r t i l i z e r 20-20) a t a r a t e o f 6 m l / 1 . Mix was a p p l i e d (20- P e te r s S o lu b le T race E lem ent o n c e d u r i n g week t h r e e a t a r a t e o f 0.3 m l/1. L ighting for t h e s e e d l i n g s came f r o m c o o l w h i t e flu o re sc e n t bu lb s ( h i g h o u t p u t 800 mA) s u s p e n d e d o n e m e t e r above the c a s e s . The p h o t o s y n t h e t i c p h o t o n f l u x d e n s i t y (PPFD) was m e a s u r e d w i t h Model L I - 1 6 0 0 , L incoln, top of th e p l a n t ban d s. a Lambda q u a n t u m s e n s o r the T he PPFD d a t a w e r e c o l l e c t e d 20 ( m i d - c a n o p y ) , an d 40 cm ( t o p c a n o p y ) 42, over 1 0 an d 55 jumol s -Lm *, The p h o t o p e r i o d was 18 h o u r s hours d a rk n e ss. in The a v e r a g e PPFD's a t 0 1 2 - w e e k g r o w i n g p e r i o d w e r e 30 , resp ectiv ely . Inc. NE) a t 0, 2 0 , an d 40 cm a b o v e t h e w eeks 1 a n d 12 an d t h e n a v e r a g e d . (low er cano py), (Licor l i g h t and 6 A i r t e m p e r a t u r e s i n t h e room d u r i n g t h e g r o w i n g p e r i o d w e r e 2 4 ° +_ 4° C . T w e lv e weeks a f t e r t h e sowing d a t e , the f iv e l a r g e s t s e e d l i n g s from e a c h s e e d l o t w ere s e l e c t e d experim ent. The e x p e r i m e n t a l d e s i g n was a r a n d o m i z e d b l o c k w ith each b lo ck or r e p l i c a t e in terv a l. having r e p r e s e n t i n g a tw o-day tim e There were f i v e r e p l i c a t e s w ith each r e p l i c a t e seven testin g fo r the trees the seven (one t r e e per s e e d lo t) . The o r d e r o f t r e e s w i t h i n e a c h r e p l i c a t e was r a n d o m . Ten d a y s w e r e n e e d e d t o t a k e g a s - e x c h a n g e m e a s u r e m e n t s on a to tal of 35 t r e e s . 81 A sc h em atic diagram of th e p l a n t g a s -e x c h a n g e system w ith i t s electro n ic com ponents is p resented in F i g u r e 4.1. The v o l u m e o f t h e s y s t e m e x c l u d i n g t h e s h u n t p a t h w a y i s 111 lite rs. blow er A i r was c i r c u l a t e d b y a b e l t - d r i v e n c e n t r i f u g a l (Paxton Corp., h o u s i n g and s e a l s . S a n ta M onica, The a i r CA) t h a t had an a i r t i g h t f l o w was d i r e c t e d through g l a s s t u b i n g w h i c h was c o n n e c t e d b y c o u p l e r s w i t h t e f l o n s e a l i n g rin g s. The p l a n t c h a m b e r a n d m i s t c h a m b e r w e r e made o f p lex ig lass. The t h e r m o m e t e r and l i t h i u m c h l o r i d e h u m i d i t y s e n s o r s were housed in a p l e x i g l a s s box. c o p p e r T 's w ith v a l v e s which r e g u l a t e d th e system . m s ~ 1. A ir v elo city th re e co il t h a t were e n c l o s e d A d ig ital centigrade i n d e p e n d e n t l y by t h e r m o m e t e r was used to d e te rm in e th e c u r r e n t sy stem te m p e r a tu re . therm ocouple a tta c h e d tem perature tra c in g system . i n an air. t e m p e r a t u r e was m o n i t o r e d instrum ents. flo w through t h e r e l a t i v e h u m i d i t y an d a i r tem perature of the c i r c u l a t i n g System a i r the a i r i n t h e p l a n t c h a m b e r a v e r a g e d 2.1 A r a d i a t o r an d h e a t i n g i n s u l a t e d box r e g u l a t e d The s h u n t s a r e A to a S arg en t re c o rd e r gave a to m onitor tem perature changes A t h e r m i s t o r was u s e d t o c o n t r o l a v a r i a b l e output v o lta g e source t h a t o p erated the h e a te r elem ent. t e m p e r a t u r e was m a i n t a i n e d in th e System a i r a t 2 4 ° +_ 0 . 5 ° C . R e l a t i v e h u m i d i t y was m o n i t o r e d b y an e l e c t r o n i c hygrom eter S ilv er in d icato r S p r i n g , MD). (Hygrodynam ics In c., A narrow -range s e n so r head w ith e i g h t t e m p e r a t u r e p o s i t i o n s was u s e d M odel 15-3001, in c o n j u n c t i o n w ith th e KEY MIST CHAMBER INFORMATION FLOW HUMIDITY C02 TEMPERATURE RECORDER RECORDER RECORDER AIR FLOW HEATER SYSTEM COMPONENTS PRESSURE RELIEF COOLER / CONDENSER MONITOR / CONTROL UNITS SHUNT PLANT HUMIDITY co2 TEMPERATURE CHAMBER . SENSOR , SENSOR SENSOR HUMIDITY CONTROL TEMPERATURE CONTROL F i g u r e 4.1 . S c h e m a t i c d i a g r a m o f t h e p l a n t g a s - e x c h a n g e s y s t e m us ed in t h e p h o to sy n th esis study. 83 hygrom eter in d icato r to o b ta in a c c u r a te r e a d in g s o f r e l a t i v e hum idity w ith in a s p e c i f i e d h u m i d i t y was t r a c e d tem p eratu re range. The r e l a t i v e on a T e x a s I n s t r u m e n t s r e c o r d e r . D e v i a t i o n s g r e a t e r t h a n 1% f r o m 65% r e l a t i v e h u m i d i t y w e r e corrected operated by a h u m i d i f i e r / d e h u m i d i f i e r c o n t r o l the m istin g and c o o l i n g (radiator) c irc u it th at u n its. S y s t e m a i r was pumped f r o m t h e s y s t e m and t h r o u g h two s i l i c a g e l c o l u m n s b e f o r e e n t e r i n g an i n f r a r e d g a s a n a l y z e r (Beckman I n s t r u m e n t s , M ode l 864) w h e r e c a r b o n d i o x i d e c o n c e n t r a t i o n s were m easured. were t r a c e d The c a r b o n d i o x i d e on a T e x a s I n s t r u m e n t s r e c o r d e r . through th e a n a ly z e r , The l i g h t t h e a i r was r e t u r n e d source for lev els A fter passing to th e sy stem . th e p l a n t chamber c o n s i s t e d of f o u r 4 0 0 -w a tt and one 1 ,0 0 0 -w a tt m e t a l h a l i d e b u l b s (S y lv a n ia M etalarc) a t t a c h e d to p a r a b o l i c aluminum r e f l e c t o r s and s u s p e n d e d a b o v e and t o t h e s i d e s o f t h e chamber. The p h o t o s y n t h e t i c photon f lu x d e n s it y (PPFD) i n s i d e t h e p l e x i g l a s s chamber a t t h e b o tto m , m i d - s e c t i o n , a n d t o p was 7 1 5 , 7 6 5 , an d 1220 jamol , resp ectiv ely . These r e a d i n g s were th e a v e r a g e o v e r t h e t e n - d a y experim ental jjmol period. The mean o f t h e s e r e a d i n g s was 900 s “ ^m"2. B efore in s e r tin g chamber, a seed lin g in th e g a s -e x c h a n g e t h e s e e d l i n g was w a t e r e d an d a c o l l a r made f r o m a s i z e 16 r u b b e r s t o p p e r w a s p l a c e d a r o u n d t h e b a s e o f t h e stem . O p to sil The seam b e t w e e n t h e s t e m an d s t o p p e r was s e a l e d w i t h (U nitek Corp., M onrovia, CA), a s i l i c o n e - b a s e d 84 m olding m a t e r i a l . lig h t The s e e d l i n g was p r e c o n d i t i o n e d i n t e n s i t y and a i r to th e f lo w i n s i d e th e p l a n t chamber f o r a p e r i o d o f 20 m i n u t e s b e f o r e t h e g a s - e x c h a n g e s y s t e m was sealed to room a i r . N e t p h o t o s y n t h e s i s o f e a c h s e e d l i n g was d e t e r m i n e d from t h e tim e p e r i o d t h a t t h e p l a n t n e ed ed to d e p l e t e t h e CO2 c o n c e n t r a t i o n 265 ppm. i n t h e g a s - e x c h a n g e s y s t e m f r o m 340 ppm t o When t h e C02 c o n c e n t r a t i o n d e c r e a s e d t o 2 65 ppm, t h e p l a n t c h a m b e r was c o v e r e d w i t h b l a c k c l o t h an d a l l l i g h t s were t u r n e d o f f . D a r k r e s p i r a t i o n was d e t e r m i n e d f r o m t h e i n c r e a s e i n C 0 2 l e v e l s i n t h e s y s t e m a f t e r 30 m in u tes of d a rk n e ss. A l l d a t a i n ppm w e r e c o n v e r t e d t o mg C02 dm” 2 h r “ l . F o llo w in g th e g a s-ex ch an g e m easurem ents, le a f area of e a c h s e e d l i n g was o b t a i n e d b y a L I - 3 0 0 0 P o r t a b l e A r e a M e t e r (LiCor In c., L incoln, n e a re st centim eter. NE). L e a v e s and s t e m s w e r e d r i e d a t 1 0 5 ° C f o r 48 h o u r s . stem s were w eighed Stem h e i g h t was m e a s u r e d to the i n an o v e n O v e n - d r y w e i g h t o f t h e l e a v e s and 0.1 g r a m . Two-way a n a l y s e s o f v a r i a n c e w e r e c a l c u l a t e d f r o m e a c h s e e d l o t an d s p e c i e s g r o u p . were a l s o c a l c u l a t e d to for data Pearson c o r r e l a t i o n s f o r r e l a t i o n s h i p s betw een th e d a t a . H ydroponic Study The h y d r o p o n i c s y s t e m u s e d t o s t u d y a s p e n r o o t g r o w t h was m o d e l e d a f t e r an i r r i g a t i o n - t y p e w a t e r c u l t u r e stu d ies t h a t was d e v e l o p e d by d e S t i g t e r m o d i f i e d b y Wood a n d H a n o v e r (1980). for root (1969) and l a t e r Wood's s y s t e m was 85 s l i g h t l y m odified to avoid m aintenance p ro blem s. was c o n s t r u c t e d The s y s t e m i n a g l a s s h o u s e and s u p p l e m e n t a l lig h tin g 1 0 s -Lm *) f r o m c o o l w h.i t e f l u o r e s c e n t t u b e s was (100 p m o l p ro v id ed . The p h o t o p e r i o d was m a i n t a i n e d T em perature ranged at 16 h o u r s . f r o m 20 °C a t n i g h t t o 25°C i n S eed f r o m t h e s e v e n s e e d l o t s th e day. used in th e g as-ex ch an g e e x p e r i m e n t w e r e sown i n 15 cm h i g h p l a s t i c c a s e s f i l l e d 60% p e r l i t e a n d 40% p e a t . s e v e n cm t a l l , w ith When t h e s e e d l i n g s w e r e f i v e t o t h e y w e r e r e m o v e d f r o m t h e c a s e s and t h e i r r o o t s w e re g e n t l y w ash ed w i t h w a t e r and p l a c e d i n 61 x 30 x 10 cm r o o t t r a y s t h a t w e r e o r i e n t e d a t a 2 0 ° a n g l e f r o m h o riz o n ta l on a g r e e n h o u s e b e n c h . co n stru cted The t r a y s w e r e f r o m 2 mm PVC s h e e t s an d had r e m o v e a b l e a l u m i n u m c o v e r s an d f a l s e b o t t o m s t o a v o i d p o o l i n g o f w a t e r a r o u n d the ro o ts . The n u t r i e n t so lu tio n p r e p a r e d 2.5 t i m e s t h e s t r e n g t h (1 98 0) f o r t h e s y s t e m was u s e d by Wood a n d H a n o v e r an d was c h a n g e d o n c e d u r i n g week 4 o f t h e 8 - w e e k experim ent. B efore p la c in g o f IN HC1 w e r e seed lin g s tray , 1 , 1 5 0 ml a d d e d t o t h e 230 l i t e r s i n t h e s y s t e m t o l o w e r t h e s o l u t i o n pH f r o m 7.8 t o 6 . 0 . experim ent, in th e D uring the course of th e a c i d was o c c a s i o n a l l y a d d e d t o m a i n t a i n t h e pH betw een 6 .0 -6 .5 . The t r a y s w e r e c o n n e c t e d 1.9 cm I.D. conducted rig id p o ly v in y l to a 2 0 0 - l i t e r c h lo rid e (PVC) f e e d e r t a n k by tubing which t h e n u t r i e n t s o l u t i o n by g r a v i t y from t h e f e e d e r t a n k to t h e t r a y s and from t h e t r a y s b a c k to a 2 0 0 - l i t e r drainage tank. Ea ch t r a y h a d three 0.9 mm I.D. trick le 86 irrig atio n c a p illa ry m atics In c., tu b es w ith b e l l W atertow n, NY) c o n n e c t i n g w ith th e top o f th e tr a y . clo th l i n e r on which s e e d l i n g from th e b o tto m t u b i n g which c a r r i e d r o o t s grew. the s o lu tio n in to the overhead The c l o t h The n u t r i e n t of each tr a y When t h e d r a i n a g e t a n k f i l l e d pump was a c t i v a t e d t h e f e e d e r PVC t u b e These tu b e s d r i p - i r r i g a t e d was 50% c o t t o n a n d 50% p o l y e s t e r . drained w e i g h t s (Chapin W a te r - into the lin er so lu tio n 1. 9 cm I.D. to th e d ra in a g e PVC tank. to the 1 2 0 - l i t e r l e v e l , a sump an d t h e n u t r i e n t s o l u t i o n was pumped up feeder tank. The n u t r i e n t s o l u t i o n then f l o w e d f r o m t h e f e e d e r t a n k and t h r o u g h a f i v e m i c r o n f i l t e r which removed p a r t i c u l a t e s . filte r, to A fter passing through the t h e n u t r i e n t s o l u t i o n e n t e r e d t h e PVC t u b i n g l e a d i n g the tr a y s and t h e c y c l e r e p e a t e d itse lf. R o o t and s h o o t m e a s u r e m e n t s b e g a n when t h e new w h i t e ro o ts of the s e e d l i n g s h a d r e a c h e d 1 0 - 2 0 cm i n l e n g t h . Roots w ere r e f e r e n c e d w ith s t a i n l e s s the ro o t tip s on t h e t o be m e a su re d . s te e l nuts p laced a t f i r s t d a y o f e a c h week t h a t g r o w t h was M easurem ents of r o o t , w e r e t a k e n o n c e a week f o r f i v e w e e k s . leaf, A fter the f i f t h w e e k , t h e l e a v e s , s t e m s , and r o o t s o f a l l h arv ested , o v en -d ried , an d w e i g h e d . w ith a L I-3 0 0 0 P o r t a b l e Area M ete r and s t e m g r o w t h s e e d l i n g s were L e a f a r e a was m e a s u r e d (LiCor, L i n c o l n , NE). The e x p e r i m e n t was a c o m p l e t e l y r a n d o m i z e d d e s i g n w i t h three tre e s per s e e d lo t. a n a l y s i s of v a r ia n c e . Data w ere a n a l y z e d by one-way C o r r e l a t i o n s were c a l c u l a t e d r e l a t i o n s h i p s betw een th e d a t a . fo r the 87 N u rse ry Study On J u n e 4 t h , 1 9 8 3 s e e d f r o m t h e s e v e n s e e d l o t s u s e d i n t h e g a s - e x c h a n g e and h y d r o p o n i c s y s t e m s w e r e sown i n a n u r s e r y in a random ized b l o c k d e s i g n w ith The s e e d l i n g s o f t h e s e v e n s e e d l o t s thinned four r e p l i c a t e s . in e a c h r e p l i c a t e were to e i g h t t r e e s p er s q u a re f o o t in J u l y . s e e d l i n g s were f e r t i l i z e d (20-20-20) six fun gi. w ith P e te rs S o il T est F e r t i l i z e r tim es d u rin g a p p l i e d o n c e a week t h e P lictran The t h e summer. B e n e l a t e was f i r s t month t o c o n t r o l d a m p i n g - o f f was s p r a y e d tw ice to c o n tr o l m ite s . Ten t r e e s per s e e d l o t in each r e p l i c a t e were ran d o m ly s e l e c t e d and h a r v e s t e d w eight, on S e p t e m b e r 2 7 t h . H eight, c a l i p e r , an d b u d n u m b e r w e r e m e a s u r e d . bud s e t , and leaf f a ll not h arv ested . variance. D ates of dry leaf flu sh , were r e c o r d e d f o r a n o t h e r te n t r e e s D ata were a n a l y z e d by two-way a n a l y s i s o f C o r r e l a t i o n s were c a l c u l a t e d fo r the d a ta . RESULTS AND DISCUSSION P h o to sy n th esis, R e sp ira tio n , and S h o o t Growth D ata from t h e p h o t o s y n t h e s i s e x p e r i m e n t a r e T a b l e 4.1. b igtooth h y brid (PN). (P. g r a n d i d e n t a t a ) , (P. trem bling Xs m i t h i i ) i n r a t e s (P. (1978). in t h i s p h y sio lo g ical trem u lo id es) , betw een PN r a t e s a s p e n a g r e e d w i t h O k a f o and T h e i r PN r a t e s w e r e s i m i l a r study. an d of n et p h o tosynthesis The l a c k o f s i g n i f i c a n t d i f f e r e n c e s o f b i g t o o t h an d t r e m b l i n g found in T h e r e w e r e no s i g n i f i c a n t d i f f e r e n c e s b e t w e e n aspen Hanover liste d H ybrid aspen s u f f e r e d ab n o rm alities to th e ones no a p p a r e n t in p h o t o s y n t h e s i s s i n c e t h e i r PN 88 r a t e s were e q u a l to tre m b lin g aspen. However, l a r g e PN r a t e s o f u p t o 15 mg C 0 2 dm “ 2 h r “ ^ r e p o r t e d f o r w h i t e p o p l a r b ig to o th aspen h y b rid s observed in t h i s study. (Domingo and G o r d o n 1974) w e r e n o t The PN r a t e s o f P. X s m i t h i i suggested t h a t genes c o n t r o l l i n g were s i m i l a r T a b l e 4.1. the p h o to sy n th e sis p ro cess in P . g r a n d i d e n t a t a and P. t r e m u l o i d e s . P h o t o s y n t h e s i s , r e s p i r a t i o n , l e a f a r e a , and p l a n t d r y w e i g h t d a t a from t h e f o u r a s p e n t a x a in th e p h o to sy n th e sis stud y. Taxa C h a r a c te r M easured N e t P h o t o s y n t h e s i s (PN) (mg C0 2 dm"2h r _ 1 ) Whole P l a n t Pj, (mg C02 h r ” 1 ) D a r k R e s p i r a t i o n (RD) (mg C02 dm” 2h r _ 1 ) Whole P l a n t Rd (mg C0 2 h r ” 1 ) r d/ p n R a t i o (no u n i t s ) T o t a l L e a f Number ( l e a v e s > 2 cm) T o t a l L eaf Area (dm” 2 ) S p e c i f i c L e af Area (dm2 g “ 1 ) PN p e r L e a f D r y W e i g h t (mg CO, h r “ 1 g " 1 ) T o t a l L e a f D ry W e i g h t (grams) S t e m D ry W e i g h t (grams) W hole P l a n t D ry W e i g h t (grams) H e i g h t (cm) . / 1 2 2 4 / q l F-V alue TXT4 S i g n i f i c a n c e GXG1 GXT2 TXG3 5.7 6.3 6.3 6.3 n.s. 61.1 73.4 70.5 58.2 * 1.3 1.2 1.2 1.5 n .s. 13.7 13.5 13.4 13.3 n .s. .2 4 .19 .20 .24 n .s. 13 19 19 31 10.8 11.7 11.1 9.2 n .s. 5.2 5.0 6.0 6.3 *** 30.2 34.8 37.8 39.6 n .s. 2.1 2.4 1.9 1.5 ★★ 0.6 0.6 0.7 0 .6 n .s. 2.7 3.0 2.6 2.1 ** 32 37 41 45 ** * l i i c i u f j ^ d ii u X 'd X c V cX o f *** l c o e'er c u X v c i y < P o p u l u s g r a n d i d e n t a t a X £ . g r a n d i d e n t a t a (x o f 10 s e e d l i n g s ) P . g r a n d i d e n t a t a X P . t r e m u l o i d e s (mean o f 5 s e e d l i n g s ) . P. t r e m u l o i d e s X P . g r a n d i d e n t a t a (mean o f 10 s e e d l i n g s ) . P . t r e m u l o i d e s X P . t r e m u l o i d e s (mean o f 10 s e e d l i n g s ) . 89 On a w h o l e p l a n t b a s i s , higher h y b r i d s h ad s i g n i f i c a n t l y n e t carbon d io x id e f ix a ti o n parent species. than e i t h e r T h i s was p r o b a b l y d u e t o t h e a r e a in th e h y b r i d s . into larg er leaf H o w e v e r , s o m e o f t h e l o w e r l e a v e s on e ach s e e d l i n g had t o be rem oved b e f o r e seed lin g o f t h e two the rubber in sertin g th e s t o p p e r , so t h i s h y p o t h e s i s c a n n o t be s u p p o r t e d by t h e d a t a . D i f f e r e n c e s among a s p e n t a x a i n d a r k r e s p i r a t i o n p e r u n i t l e a f a r e a and t o t a l d a r k r e s p i r a t i o n n o n - s i g n i f i c a n t in t h i s a ls o been re p o rte d study. and t h e b l a c k a n d b a l s a m p o p l a r s and K o z l o w s k i S p ecific Dark r e s p i r a t i o n r a t e s h a v e t o b e n o n - s i g n i f i c a n t among a s p e n s p e c i e s (O k a fo and H a n o v e r 197 8) (Luukkanen p e r p l a n t were 1972). l e a f a r e a was h i g h , an d s i g n i f i c a n t d i f f e r e n c e s e x i s t e d betw een s e e d l i n g s w ith e i t h e r b i g t o o t h or tre m b lin g aspen as m a te rn a l p a r e n ts . The l o w l i g h t i n t e n s i t y o f t h e g r o w t h f r a m e an d t h e a b s e n c e o f w in d produced a s h a d e - l e a f m orphology in th e l e a v e s . an d H a n o v e r area (1978) in t h e s e thickness) affected aspen. m aternal f o u n d no d i f f e r e n c e s two s p e c i e s , s p e c i f i c by t h e a r t i f i c i a l T h i s was a l s o lig h tin g ev ident in s p e c i f i c le a f area in b i g t o o t h a s p e n from t h i s S i n c e O kafo leaf (le af s t u d y was l e s s t h a n was t r e m b l i n g in t h e h y b r i d s w ith b i g t o o t h parentage. Not s u r p r i s i n g l y , t r e e s w ith b ig to o th m a te rn a l p a r e n t a g e a l s o ha d s i g n i f i c a n t l y h i g h e r H o w e v e r , PN p e r l e a f d r y w e i g h t was l e s s l e a f dry w eight. in t h e s e trees. 90 S elf-shad ing com parison, h y b rid s. higher by t h e l a r g e l e a v e s may h a v e b e e n a f a c t o r . s t e m d r y w e i g h t was s i m i l a r Shoot (stem + l e a v e s ) in a l l species In and d r y w e i g h t was s i g n i f i c a n t l y i n b i g t o o t h a s p e n and t h e h y b r i d s . D espite having l e s s l e a f a r e a , l e a f d r y w e i g h t , and s h o o t d r y w e ig h t th a n b i g t o o t h a s p e n and t h e h y b r i d s , t h e h i g h e s t PN p e r tre m b lin g aspen did p o sse ss l e a f d r y w e i g h t an d t h e r e f o r e , was t h e most p h o t o s y n t h e t i c a l l y e f f i c i e n t s p e c i e s . C o r r e l a t i o n s b e t w e e n t h e g a s - e x c h a n g e d a t a showed t h a t PN was s i g n i f i c a n t l y c o r r e l a t e d a t t h e 5% l e v e l w i t h h e i g h t (r=.39) but nothing e l s e . PN was p o s i t i v e l y c o r r e l a t e d w ith l e a f ( r = . 0 5 ) , s te m ( r = . 3 2 ) , and s h o o t ( r =.12) d r y w e i g h t . A l t h o u g h s m a l l and n o n - s i g n i f i c a n t , these p o s itiv e c o r r e l a t i o n s were c o n t r a r y to t h e n e g a t i v e c o r r e l a t i o n s reported b y O k a f o an d H a n o v e r (1978) b e t w e e n PN and d r y m a t t e r p r o d u c t i o n trem bling for the r e l a t i o n s h i p i n b i g t o o t h an d aspen. W h o l e p l a n t p h o t o s y n t h e s i s was s i g n i f i c a n t l y c o r r e l a t e d a t t h e 1% l e v e l w ith l e a f w e ig h t ( r = .6 7 ) , stem w e ig h t ( r = .6 9 ) , s h o o t w e ig h t ( r = .7 1 ) , l e a f a r e a ( r = .6 2 ) , and sp ecific leaf area (r=-.45). was s i g n i f i c a n t l y c o r r e l a t e d (r= .3 4 ), and T otal p la n t dark r e s p i r a ti o n a t t h e 5% l e v e l for le a f area l e a f d r y w e i g h t ( r = .3 9 ) , stem d r y w e i g h t ( r = .3 8 ) , shoot d ry w eight (r= .41). D ark r e s p i r a t i o n rates s i g n i f i c a n t l y and i n v e r s e l y c o r r e l a t e d a t t h e 5% l e v e l (r=-.37) w ith leaf area. were 91 These c o r r e l a t i o n s s u g g e s t t h a t a s p e n s e e d l i n g s which h a v e b o t h h i g h P N r a t e s and l a r g e l e a f a r e a s w i l l a s s i m i l a t e t h e most d r y m a t t e r . A pplying t h i s h y p o th e s is to the d a ta i n T a b l e 4 . 1 , t h e two a s p e n h y b r i d s s h o u l d h a v e p r o d u c e d more d r y m a t t e r than t h e two p a r e n t s p e c i e s . p r o d u c t i o n b y t h e h y b r i d s was i n d e e d e q u a l Shoot biom ass or s u p e rio r t h e b i o m a s s p r o d u c e d by b i g t o o t h an d t r e m b l i n g to aspen. However, i t was n o t known how much r o o t b i o m a s s was p r o d u c e d which i s very im portant because of the c lo n a l h a b it of aspens. A p r o b l e m w i t h t h e PN a n d l e a f a r e a h y p o t h e s i s w a s t h a t trem b lin g aspen, the t a l l e s t . estim atin g w hich had t h e l o w e s t d r y w e i g h t , was a l s o The i m p o r t a n c e o f PN m e a s u r e m e n t s f o r fie ld p ro d u ctiv ity is d eb atab le. G ifford (1974) argued t h a t h ig h p h o t o s y n t h e t i c e f f i e n c y becomes i r r e l e v a n t by th e tim e a l l o th er p h y s io lo g ic a l p ro c e sse s have i n t e r a c t e d w ith p l a n t grow th. Ceulem ans e t a l . (1980) r e p o r t e d t h a t t h e PN m e a s u r e m e n t b y i t s e l f was n o t s i g n i f i c a n t l y c o r r e l a t e d w ith f i e l d p o p lar clones. However, a later p r o d u c tiv ity of six s t u d y ( C e u l e m a n s an d I m p e n s 1 9 8 3 ) w i t h 18 p o p l a r c l o n e s s h o w e d PN r a t e s t o b e s i g n i f i c a n t l y c o r r e l a t e d w ith f i r s t - y e a r co n trast, le a f area index shoot len g th . ( A n d e r s o n 1979) and In le a f area ( I s e b r a n d s a n d N e l s o n 1982) h a v e b e e n shown t o b e l i n e a r l y related to p o p la r biom ass p ro d u c tio n . grow th i s e s s e n t i a l genes th a t c o n tro l for S ince ra p id shoot i n t o l e r a n t s p e c ie s such as aspen, c e l l d i v i s i o n s in th e p e r i p h e r a l (leaf) 92 and a p i c a l ( s h o o t ) m e r i s t e m s may b e c o n s i d e r a b l y m o r e i m p o r t a n t t h a n g e n e s w h i c h r e g u l a t e C02 f i x a t i o n (net p h o to sy n th esis). H y d r o p o n ic s : P l a n t Growth and Biom ass P a r t i t i o n i n g A pical l e a f p ro d u ctio n of h y d ro p o n ic ally -g ro w n seed lin g s species varied little and h y b r i d betw een th e fo u r (Fig. least. A pical in term ed iate, 4.2), but d iffered s p e c i e s and h y b r i d s . p ro d u ced t h e most a p i c a l the f ro m week t o week w i t h i n e a c h a s p e n sig n ific a n tly Trem bling aspen l e a v e s p e r week and b i g t o o t h a s p e n l e a f p r o d u c t i o n i n t h e h y b r i d s was a l t h o u g h l e a f nu m b er m o r e c l o s e l y c o r r e s p o n d e d to th e number o f l e a v e s o f th e m a t e r n a l p a r e n t . of le a v e s (in c lu d in g branch le a v e s) s ig n i f i c a n t l y higher an d t o t a l in t h e t r e m b l i n g The n u m b e r l e a f a r e a were x b ig to o th hy b rid s ( T a b l e 4.2) b e c a u s e t h i s h y b r i d and t r e m b l i n g aspen averaged 7 and 6 b r a n c h e s , r e s p e c t i v e l y , w h e r e a s b r a n c h e s w e r e a b s e n t i n b i g t o o t h a s p e n and t h e b i g t o o t h x t r e m b l i n g h y b rid s. T herefore, genes re g u la tin g w e r e n o n - a d d i t i v e and h a v e a m a t e r n a l (GxT) e a r l y branch form ation o rig in . A l t h o u g h l e a f a r e a was s i g n i f i c a n t l y l a r g e r i n trem bling x b ig to o th (TxG) h y b r i d s , the co rrelatio n (r=.79) b e t w e e n h y b r i d l e a f a r e a and s h o o t d r y w e i g h t was h i g h b u t not s ig n i f i c a n t ( T a b le 4.3). b ig to o th an d (r=.92) can tly co rrelated trem bling However, aspen le a f area (r=.88) and p l a n t sig n ifi­ a t t h e 1% l e v e l w i t h s h o o t d r y w e i g h t . L e a f a r e a was a l s o s i g n i f i c a n t l y c o r r e l a t e d ( r = . 88) were of both ( r = .9 4 ) dry w eight for a ll w ith r o o t sp ecies 93 com bined. sp ecific B i g t o o t h and t r e m b l i n g a l s o ha d s l i g h t l y le a f areas T a b l e 4.2. (heavier leaves) low er than the h y b rid s . S h o o t an d r o o t m e a s u r e m e n t s o f t h e f o u r a s p e n t a x a f r o m t h e h y d r o p o n i c s t u d y a f t e r week 5 . Taxa GXG1 GXT2 TXG3 TXT4 F-V alue S igni fic a n c e Number o f L e a v e s 17 22 88 68 ** L e a f Area 31 57 86 52 ** 3.6 3.9 3.9 3.4 55 71 101 92 ** Number o f B r a n c h e s 0.0 0.2 7.2 6.2 * Number o f 1 ° R o o t s 12 16 17 15 n .s. Mean R o o t G r o w t h o f P r i m a r y R o o t s (cm) 59 73 74 61 n.s. Mean Number o f 2 ° R oots P er 1° Root 204 212 227 148 ** R o o t t o S te m R a t i o 1.1 1.0 0.6 0 .5 ** Root t o Stem +Leaf R atio .29 .28 .21 .19 ** C h a r a c t e r M easured (dm^) S p e c i f i c L eaf Area (dm g ) H eight (cm) n.s. * / * * S i g n i f i c a n t a t t h e 5 a n d 1% l e v e l s , r e s p e c t i v e l y . ^ P o p u l u s g r a n d i d e n t a t a X P . g r a n d i d e n t a t a (x o f 6 s e e d l i n g s ) . 2 P . g r a n d i d e n t a t a X P . t r e m u l o i d e s (mean o f 3 s e e d l i n g s ) . 3 P . t r e m u l o i d e s XP . g r a n d i d e n t a t a (mean o f 6 s e e d l i n g s ) . 4 P. t r e m u l o i d e s XP . t r e m u l o i d e s (mean o f 6 s e e d l i n g s ) . W eekly h e i g h t h yb rids ex h ib ite d increm ent (Fig. 4.3) a norm al grow th c u rv e . in a l l s p e c i e s and H eight d i f f e r e n c e s ( T a b l e 4. 2) w e r e s i g n i f i c a n t a t t h e 1% l e v e l , a n d t o t a l h e i g h t was g r e a t e s t i n t h e TxG h y b r i d s . In a d d i t i o n to the LEAF PRODUCTION PER WEEK 9 N U M B E R 6 7 BIOTOOTH X BIOTOOTH B—BBIOTOOTH X TREMBLINB ♦— ♦TREMBLING X BIOTOOTH * ” ** TREMBLING X TREMBLING 6 0 F 5 N E W 4 L E 3 EL tr fl V E S 2 1 0 1 2 3 4 5 WEEK F i g u r e 4. W e e k ly a p i c a l h y b rid s. l e a f p r o d u c t i o n o f h y d r o p o n i c a l l y - g r o w n a s p e n and a s p e n HEIGHT INCREMENT (CM) PER WEEK 20 H E I G H T I N C R E M E N T BIGTOOTH X BIGTOOTH Q—BBIGTOOTH X TREMBLING «— 4 TREMBLING X BIGTOOTH * —* TREMBLING X TREMBLING 18 16 . S ------ 14 . 12 _ 10 I N 8 _ C M 6 . ! 1 1 1 1 2 3 4 1--------- 5 WEEK F i g u r e 4 . 3. Weekly h e i g h t i n c r e m e n t o f h y d r o p o n i c a l l y - g r o w n a s p e n and a s p e n h y b r i d s 96 h etero sis in th ese h y b rid s, the GxT h y b r i d s a l s o g r e w b e t t e r th a n what a d d i t i v e e f f e c t s a l o n e c o u ld e x p l a i n . a d d itiv e genetic variance T his non­ in h e i g h t g row th f u r t h e r s u p p o rte d t h e f i n d i n g s o f l a r g e amounts o f n o n - a d d i t i v e v a r i a n c e the l e a f nu m ber and le a f area d ata. P r i m a r y r o o t p r o d u c t i o n was s l i g h t l y trem bling a s p e n and t h e h y b r i d s t h a n (T a b le 4.2). Genes f o r aspen to be dom inant to appear W eekly r o o t g ro w th in itia lly (Fig. greater prim ary 4.4) g reater two s p e c i e s . in in b i g t o o t h a sp en root those in itiatio n in trem bling in b i g t o o t h a s p e n . of th e prim ary r o o t s was i n t h e two h y b r i d s , b u t b y week 5, t h e r a t e o f r o o t g r o w t h i n t h e h y b r i d s h ad d e c r e a s e d the in to t h a t of R o o t g r o w t h i n t h e two a s p e n s p e c i e s rem ained s t a b l e o v e r th e f iv e - w e e k - p e r io d . T h e r e w e r e no s i g n i f i c a n t d i f f e r e n c e s among t h e s p e c i e s an d h y b r i d s i n to tal p rim ary r o o t grow th a f t e r T a b l e 4.3. f i v e weeks. C o r r e l a t i o n s b e t w e e n l e a f a r e a an d p l a n t d r y w e i g h t o f a s p e n s e e d l i n g s gro w n i n t h e h y d r o p o n i c s y s t e m . L e a f A rea o f Each Taxa P l a n t Biom ass Populus Populus Populus A ll g r a n d i d e n t a t a 1 Xsmi t h u 2 t r e m u l o i d e s 3 S p e c i e s 4 ------------------------------------------- r ----------------------------------------- S h o o t Dr y W e i g h t R o o t Dry W e i g h t T o t a l Dry W e i g h t */** S i g n i f i c a n t a t 1 d . f . = 6. 2 d . f . = 9. 3 d . f . = 6. 4 d . f . = 21. . 9 2 ** . 9 2 ** . 9 5 ** .79 ns .86 * .8 4 * t h e 5 and 1% l e v e l s , . 8 8 ** . 9 1 ** . 9 7 ** resp ectiv ely . . 8 8 ** . 8 8 ** .9 4 ** ROOT GROWTH (CM) OF PRIMARY ROOTS PER WEEK 20 BIGTOOTH X BIGTOOTH B - -BBIGTOOTH X TREMBLING R 0 0 TREMBLING X BIGTOOTH “* TREMBLING X TREMBLING 18 . T T I P G R 0 16 . az: 14 _ W T H I N C M 12 . 10 . \ 8 \ , , 1 1 1 2 3 4 \ 1---------- 5 WEEK F i g u r e 4 . I. Weekly p r i m a r y r o o t g r o w t h o f h y d r o p o n i c a l l y - g r o w n a s p e n and a s p e n hy b rid s. 98 Secondary r o o t p ro d u ctio n ( T a b l e 4. 2) was s i g n i f i c a n t l y g reater i n b i g t o o t h a s p e n an d t h e h y b r i d s t h a n aspen. In c o n t r a s t to prim ary r o o t p ro d u c tio n , secondary ro o t p ro d u c tio n those in t r e m b lin g aspen. in tr e m b l i n g genes for in b i g t o o t h aspen were dom inant to Secondary r o o t p ro d u c tio n per week ( F i g . 4.5) d e c r e a s e d fro m w e e k s 1 t o 4 and t h e n stab ilized . The d e n s i t y o r number o f s e c o n d a r y r o o t s p e r cm of p rim ary ro o t d e c re a se d and began to l e v e l over the o f f i n w e e k 5. five-w eek-period (Fig. 4.6) T h e r e w e r e no s i g n i f i c a n t d i f f e r e n c e s among t h e s p e c i e s and h y b r i d s . The r o o t d a t a sh ow ed t h a t t r e m b l i n g a s p e n p r o d u c e d more p r i m a r y r o o t s an d l e s s However, Okafo r o o t g r o w t h r a t e s w e r e t h e same i n t h e two s p e c i e s . (1976) and t r e m b l i n g A fter secondary ro o ts than b ig to o th aspen. found s i m i l a r r o o t grow th p a t t e r n s in b ig to o th a s p e n s e e d l i n g s grown in a s o i l e s s m e d ia . f i v e weeks, b o th h y b r id s i n t h e p r e s e n t s t u d y had p r o d u c e d s l i g h t l y m o r e p r i m a r y an d s e c o n d a r y r o o t s t h a n e i t h e r b ig to o th or tre m b lin g aspen, b u t ro o t p ro d u ctio n in t h e s e h y b r id s had d e c l i n e d to th e r a t e s of th e p a r e n t s p e c i e s b y week 5. Carbon p a r t i t i o n i n g (Fig. 4. 7) betw een the stem , and r o o t s was s i g n i f i c a n t l y d i f f e r e n t a t t h e 1% l e v e l b ig to o th , ratio s trem bling, and h y b r i d a s p e n , an d t h e r o o t an d r o o t t o s t e m + l e a f r a t i o s h ighly s ig n ific a n t. p a rtitio n e d equal ( T a b l e 4.2) leaves, among to stem were a l s o B i g t o o t h a s p e n and GxT h y b r i d s a m o u n t s o f c a r b o n t o t h e s t e m an d r o o t s . On t h e o t h e r h a n d , t r e m b l i n g a s p e n and TxG h y b r i d s SECONDARY ROOT PRODUCTION PER WEEK 80 70 _ N E W BIOTOOTH X BIGTOOTH BIGTOOTH X TREMBLING ♦ —<* TREMBLING X BIGTOOTH * - - * TREMBLING X TREMBLING b— s R 0 0 T S 50 - P E R 40 . H E E K 30 . io I 3 7 5 WEEK F i g u r e 4. 5. W e e k ly s e c o n d a r y r o o t p r o d u c t i o n o f h y d r o p o n i c a l l y - g r o w n a s p e n and h y b rid s. DENSITY OF SECONDARY ROOTS (PER CM OF PRIMARY ROOT) 7 A— * BIGTOOTH X BIGTOOTH 0 ® BIGTOOTH X TREMBLING TREMBLING X BIGTOOTH * - - * TREMBLING X TREMBLING s E C 6 0 N 0 5 fl R Y R 4 n 'A 's . \ 0 0 T S 3 P E R 2 C M 1 0 I 2 3 4 5 WEEK F i g u r e 4. Number o f s e c o n d a r y r o o t s p e r cm o f p r i m a r y r o o t o f h y d r o p o n i c a l l y - g r o w n a s p e n and a s p e n h y b r i d s . CARBON PARTITIONING (OVEN-DRY HEIGHT IN GRAMS) 40 35 H E I G H T 30 □ BIGTOOTH X BIGTOOTH m i l BIGTOOTH X TREMBLING TREMBLING X BIGTOOTH TREMBLING X TREMBLING I 25 I N 20 G R A 15 M S 10 5 i **** 0 ROOTS STEM LEAVES T TOTAL PLANT ORGAN F i g u r e 4.7 . C o m p a r a t i v e c a r b o n p a r t i t i o n i n g b e tw e e n t h e r o o t s , s t e m , and l e a v e s o f h y d r o p o n i c a l l y - g r o w n a s p e n and a s p e n h y b r i d s . 102 p a rtitio n ed to t w i c e a s much c a r b o n t o t h e s t e m t h a n t h e y d i d the ro o ts . They a l s o had f i v e in th e sh o o t than th e ro o t. was 3.5 t o t i m e s a s much d r y m a t t e r T h i s same s h o o t t o root ra tio 1 f o r b i g t o o t h a s p e n and t h e GxT h y b r i d s . The p h y s io lo g ic a l p ro c e sse s causing t r a n s lo c a tio n of photosynthate stro n g ly to th e m e r is te m a tic in flu e n c e d by m a te rn a l sinks appeared (cytoplasm ic) to be effects in t h e h y b rid s. T h e s h o o t t o r o o t r a t i o s o f t r e m b l i n g a s p e n a n d t h e TxG h y b rid s in t h i s reported poplars. for s tu d y were co m p arab le b y G o r d o n an d P r o m n i t z (1 976) A high sh o o t to ro o t r a t i o in te n siv e po p lar c u ltu re to th e r a t i o s for (6:1 ) field -g ro w n is a d e sirab le (Dickmann 1 9 7 5 ) . tra it I f hydroponic s t u d i e s c o u ld a c c u r a t e l y d e t e c t g e n e t i c d i f f e r e n c e s betw een dry m atter p a r titio n in g screening p a t t e r n s in s p e c ie s or c l o n e s , f o r h ig h s h o o t to r o o t r a t i o s would be p o s s i b l e . The p r e c i s i o n o f t h i s t e s t s y s t e m , h o w e v e r , w i l l d e p e n d upon how t h e g e n o t y p e x e n v i r o n m e n t i n t e r a c t i o n p artitio n in g h y b rid s. p artly a f f e c t s carbon in ea c h s p e c i e s or c l o n e . D ifferences variance early in t h e amount o f n o n - a d d i t i v e g e n e t i c f o r d r y m a t t e r p r o d u c t i o n were found The TxG h y b r i d s had t h e i n t h e two l a r g e s t d ry m a tte r biom ass, because o f overdom inant e f f e c t s (h etero sis). Under t h e n e a r o p tim u m g r o w i n g c o n d i t i o n s o f t h e h y d r o p o n i c s y s t e m a n d g l a s s h o u s e , n o n - a d d i t i v e g e n e t i c v a r i a n c e was e x p r e s s e d i n many l e a f , ad d itiv e stem , an d r o o t t r a i t s in t h e s e h y b r id s . e f f e c t s w e r e a l s o e v i d e n t i n t h e GxT h y b r i d s , Non­ 103 a l t h o u g h no o v e r d o m i n a n t e f f e c t s w e r e p r e s e n t . The i n t e r m e d i a c y o f p l a n t d r y w e i g h t f o r t h e GxT h y b r i d s i n relatio n to th e d ry w e ig h ts o f b i g t o o t h and t r e m b l i n g a s p e n i n d i c a t e a d d i t i v e g e n e t i c e f f e c t s were a l s o in v o lv ed in carbon a s s im ila tio n w ith in th e h y b r id s . N u r s e r y Growth D ata The h e i g h t g r o w t h r a n k i n g s o f t h e a s p e n s p e c i e s and h y b r i d s grown in t h e n u r s e r y w ere i d e n t i c a l to t h o s e o f t h e indoor p h y sio lo g y s tu d ie s h yb rids e x h ib ite d no h e t e r o s i s . fic a n tly co rrelated calip er (r= .91). m ediate (ad d itiv e t r a i t s m easured, Table 4 . 4 . ( T a b l e 4 .4) e x c e p t t h a t t h e TxG S tem d r y w e i g h t was s i g n i ­ a t t h e 1% l e v e l E xcluding c a l i p e r , effects) w i t h h e i g h t ( r = . 8 6 ) and th e h y b r i d s were in ter­ to th e p a r e n t s p e c i e s in th e grow th a l t h o u g h s m a l l m a t e r n a l e f f e c t s were p r e s e n t . Mean g r o w t h d a t a o f 40 s e e d l i n g s f o r e a c h o f f o u r a s p e n t a x a gro w n i n t h e n u r s e r y f o r o n e y e a r . H eight (cm) C aliper (mm) Populus g ran d id en tata 57 6.4 7.4 34.5 P .g ra n d id e n ta ta X P .trem u lo id es 67 7.3 9.6 52.5 P .trem u lo id es X P .g ran d id en tata 74 7.3 11.1 59.0 P .trem u lo id es 82 7.2 15.3 60. 5 S ig n ificance of F-V alue ** * ** Taxa Bud Number * / * * S i g n i f i c a n t a t t h e 5 an d 1% l e v e l s , S tem Dry W e i g h t ( g ra m s ) resp ectiv ely . 104 Phenology d a ta ( T a b l e 4.5) in term ed iacy of the h y b rid s. s e t an d l e a f f a l l ) ag ain dem onstrated However, grow th c e s s a t i o n These n o n - a d d i t i v e e f f e c t s were i n f l u e n c e d by c h a n g e s in e n v i r o n m e n t a l such as th o se T able 4 . 5 . (bud i n t h e GxT h y b r i d s was s t r o n g l y i n f l u e n c e d by t h e b i g t o o t h p a r e n t . and t h e r e f o r e , the stim u li would n o t be e v i d e n t in u n ifo rm e n v ir o n m e n ts in th e p h y s i o l o g i c a l stu d ies. Mean p h e n o l o g y d a t a o f 40 s e e d l i n g s f o r e a c h o f f o u r a s p e n t a x a g row n i n t h e n u r s e r y . Phenology C h a r a c t e r s * '2 Leaf Flush (Days) Taxa P opulus g ran d id en tata Bud Set (Days) Leaf F all (Days) L e a f Area D uration (Days) S tem E longation (Days) 10 136 187 177 126 P .g ra n d id e n ta ta X P .trem u lo id es 8 136 185 177 128 P .trem u lo id es X P .g ran d id en tata 6 140 190 184 134 P .trem u lo id es 5 146 206 201 141 * A l l p h e n o l o g y c h a r a c t e r s w e r e s i g n i f i c a n t l y d i f f e r e n t among a s p e n t a x a a t t h e 1% l e v e l . 2 Days t o l e a f f l u s h , b u d s e t , an d l e a f f a l l w e r e b a s e d on May 1 st as the f i r s t day. C onclusions Many s h o o t a n d r o o t t r a i t s i n t h e h y b r i d s f r o m t h e p h o t o s y n t h e s i s and h y d r o p o n i c s t u d i e s e x h i b i t e d genetic variance. pronounced n o n -ad d itiv e N o n - a d d i t i v e v a r i a n c e was n o t a s in t h e n u r s e r y - g r o w n h y b r i d s . The c o n t r o l l e d 105 e n v iro n m e n ts appeared to enhance th e n o n - a d d i ti v e e f f e c t s which p r o b a b l y c o n t r i b u t e d rankings to th e d i f f e r e n c e s in the s p e c ie s for p l a n t dry w eights over the th re e stu d ies. A l a r g e p o r t i o n of t h i s grow th v a r i a t i o n m ight be a t t r i b u t a b l e to e n v iro n m e n ta l lig h tin g because tre e s from t h e p h o t o s y n t h e s i s s t u d y had " s h a d e - l e a v e s " , t r e e s w ith " s u n - le a v e s " stu d ies. This s i t u a t i o n The r e s u l t s in c o n t r a s t to i n t h e h y d r o p o n i c and n u r s e r y p ro b a b ly confounded from t h e s e t h r e e the r e s u l t s . s t u d i e s do i n d i c a t e th at h e i g h t grow th d i f f e r e n c e s betw een aspen s p e c i e s can be e v a l ­ uated e a r l y w ith b a s ic p h y s io l o g i c a l sp ecific p h y sio lo g ical processes s t u d i e s ; how ever, (ie ., using n et photosynthesis) to s c r e e n f o r p o t e n t i a l g r o w t h r a t e in a s p e n s was n o t f o u n d t o be e f f e c t i v e . The u t i l i t y of th ese b a s ic s tu d ie s to s e l e c t f a s t - g r o w i n g t r e e s was p r o b a b l y d e p e n d e n t upon t h e a m o u n t o f ad d itiv e tra it. and n o n - a d d i t i v e g e n e t i c v a r i a n c e i n h e r e n t i n e a c h F ield t e s t s o f P. g r a n d i d e n t a t a , P. P. X s m i t h i i h a v e shown a d d i t i v e e f f e c t s but n o n -ad d itiv e e f fe c ts p h y sio lo g ical tra its trem u lo id es, fo r h e ig h t grow th, for s p e c i f i c m orphological (R eighard 1984). N on-uniform e n v i r o n m e n t s may n e u t r a l i z e o r r e d u c e e p i s t a t i c p lasm ic e f f e c t s , t h e r e b y , m aking i t d i f f i c u l t from c o n t r o l l e d e n v i r o n m e n t a l s t u d i e s grow th p o t e n t i a l in n a t u r a l and (n atu ral) and c y t o ­ to use d a ta for p ro je c tin g sp ecies environm ents. Before desig n in g p h y s i o l o g i c a l e x p e rim e n ts to d e te rm in e grow th p o t e n t i a l aspens, a t h o r o u g h u n d e r s t a n d i n g o f how e n v i r o n m e n t a l c o n d itio n s a f f e c t gene e x p ressio n and s h o u ld be g a in e d . in 106 LITERATURE CITED A n d e r s o n , H.W. 1979. Biomass p r o d u c t i o n o f h y b r i d p o p l a r grown i n m i n i r o t a t i o n . IN / P o p l a r r e s e a r c h , management an d u t i l i z a t i o n i n C a n a d a . D . C . F . F a y l e , L. Z s u f f a and H.W. A n d e r s o n ( e d . ) . O n t . M in . N a t u r a l R e s o u r c e , F o r e s t R e s . I n f o r m . P a p . No. 1 0 2 . R e p . 1 1 . 1 3 p p . C e u l e m a n s , R. an d I . I m p e n s . 1 98 3. N et CO2 e x c h a n g e r a t e and s h o o t g r o w t h o f y o u n g p o p l a r (P o p u l u s ) c l o n e s . J. Expt. B ot. 3 4 :866-870. C e u l e m a n s , R . , I . I m p e n s , F. H e b r a n t , a n d R. M o e r m a n s . 1980. E v a lu a tio n of f i e l d p r o d u c tiv ity of s e v e ra l p o p lar clones b a s e d on t h e i r g a s e x c h a n g e v a r i a b l e s d e t e r m i n e d u n d e r lab o rato ry co n d itio n s. P h o to sy n th e tic a 14:355-362. D ickm ann, D.I. 1975. P la n t m a te r ia ls a p p ro p ria te for i n t e n s i v e c u l t u r e o f wood f i b r e i n t h e N o r t h C e n t r a l Region. Iowa S t a t e J . R e s . 4 9 : 2 8 1 - 2 8 6 . Domingo, I . L . an d J .C . G o r d o n . 1974. P h y sio lo g ic a l responses o f a n a s p e n - p o p l a r h y b r i d t o a i r t e m p e r a t u r e and s o i l m o istu re. B o t. Gaz. 1 3 5 :1 8 4 -1 9 2 . G a t h e r u m , G.E., J .C . G o r d o n , a n d B .F .S . B r o e r m a n . 1967. E f f e c t s o f c l o n e an d l i g h t i n t e n s i t y on p h o t o s y n t h e s i s , r e s p i r a t i o n , and g ro w th o f a s p e n - p o p l a r h y b r i d s . S ilv ae G enetica 16:128-132. G i f f o r d , R.M. 1974. A com parison of p o t e n t i a l p h o to s y n th e s is , p r o d u c t i v i t y , and y i e l d o f p l a n t s p e c i e s w i t h d i f f e r i n g p h o to s y n th e tic m etabolism . A u s t r a l . J. P l a n t P h y s i o l . 1:107-117. G o r d o n , J .C . an d L.C. P r o m n i t z . 1976. A p h y sio lo g ical a p p r o a c h t o c o t t o n w o o d y i e l d i m p r o v e m e n t . I N / P r o c . Symp. on Cottonw ood and R e l a t e d S p e c i e s . B.A. T h i e l g e s and S .B . L a n d , J r . ( e d . ) , L o u i s S t . U n i v . , B a t o n R o u g e , pp. 66-88. I s e b r a n d s , J.G. an d N.D. N e l s o n . 1982. Crown a r c h i t e c t u r e o f s h o r t - r o t a t i o n , i n t e n s i v e l y c u l t u r e d P o p u lu s I I . Branch m o r p h o l o g y an d d i s t r i b u t i o n o f l e a v e s w i t h i n t h e c r o w n o f P o p u lu s ' T r i s t i s ' as r e l a t e d to biom ass p r o d u c tio n . Can. J . F o r. R es. 1 2 :8 5 3 -8 6 4 . L u u k k a n e n , 0 . an d T.T. K o z l o w s k i . 1972. Gas e x c h a n g e P opulus c l o n e s . S ilv a e G en etica 21:220-229. O k a f o , O.A. 1976. C om parative p h y sio lo g y t r e m b l i n g a s p e n (P o p u l u s t r e m u l o i d e s a s p e n (P o p u l u s g r a n d i d e n t a t a M ic h x . ) p o p u latio n s. Ph.D . T h e s i s , M ichigan in six and d e v e l o p m e n t o f M ic h x .) and b i g t o o t h from M ic h ig a n S t . U n i v . 103 p p . 107 O k a f o O.A. an d J.W. H a n o v e r . 1 9 78. C om parative p h o to s y n th e s is and r e s p i r a t i o n o f t r e m b l i n g an d b i g t o o t h a s p e n s i n r e l a t i o n t o g r o w t h and d e v e l o p m e n t . F o r. S c i. 24:103-109. R e i g h a r d , G.L. 1984. P hysiological g en etics stu d ies of P o p u l u s g r a n d i d e n t a t a , P. t r e m u l o i d e s , a n d t h e i r h y b r i d , X sm ith ii. P h . D . T h e s i s , M i c h i g a n S t . U n i v . 110 p p . d e S t i g t e r , H.C.M. 1969. A v ersatile c u l t u r e fo r ro o t-g ro w th s tu d ie s . 60:289-295. W ood, B.W. a n d J.W. H a n o v e r . 1980. m aple in a h y d ro p o n ic s y ste m . ir r ig a tio n - ty p e w aterZ. P f l a n z e n p h y s i o l . Root g ro w th o f s u g a r For. S c i. 26:231-237. Z a v i t k o v s k i , J. 197 1. Dr y w e i g h t a n d l e a f a r e a o f a s p e n t r e e s in n o r th e rn W isconsin. XVth IUFRO C o n g r e s s . U n i v . o f F l o r i d a , G a i n e s v i l l e , FL. M a rc h 1 5 - 2 0 . p p . 1 9 1 - 2 0 5 . CONCLUSIONS AND RECOMMENDATIONS S u c c e s sfu l e s ta b lis h m e n t of p l a n t a t i o n s of aspen (P o p u l u s t r e m u l o i d e s , fie ld sites P. g r a n d i d e n t a t a , P. X s m i t h i i ) on O l d ­ i n M i c h i g a n was a c h i e v e d when good weed c o n t r o l w i t h o u t e x c e s s i v e h e r b i c i d e damage w ere com bined. Deep- p l a n t i n g a s p e n s e e d l i n g s 15 cm a b o v e t h e r o o t c o l l a r was n o t d eleterio u s p lan tatio n s, an d r e d u c e d h e r b i c i d e d a m a g e . herbicide i n j u r y , d e e r b r o w s i n g , an d S a p e r d a damage s i g n i f i c a n t l y a f f e c t e d first two y e a r s . an d g r o w t h d u r i n g t h e t o S e c t i o n L e u c e s p e c i e s and s o i l - in tera ctio n s F urtherm ore, su rv iv al More r e s e a r c h on t h e t o x i c i t y o f p r e - em ergent h e r b ic id e s herb icide H o w e v e r , a t some in n o n - a g r i c u l t u r a l so ils a re needed. a s p e n s h o u l d n o t b e p l a n t e d on s i t e s w h e r e s e e d l i n g s a r e n o t v i g o r o u s e n o u g h t o o u t g r o w d e e r and S a p e r d a dam a g e w i t h i n two t o t h r e e y e a r s . S ig n ific a n t g en etic v a ria tio n i n g r o w t h r a t e was f o u n d b e t w e e n and w i t h i n f a m i l i e s o f P. t r e m u l o i d e s , P. g ran d id en tata, an d t h e h y b r i d s . The 20 b e s t f a m i l i e s (top 10%) a v e r a g e d 25% a b o v e t h e m e a n f o r b o t h h e i g h t a n d d ia m e te r grow th a f t e r tw o g r o w i n g s e a s o n s i n t h e fie ld . A g e - a g e c o r r e l a t i o n s b e t w e e n a g e s o n e and t h r e e w e r e m oderate b u t s i g n i f i c a n t . T herefore, p l a n t a t i o n s a re the o b j e c t i v e , p o s s i b l e by s e l e c t i n g if sh o rt-ro tatio n some g a i n i n y i e l d may b e t h e b e s t f a m i l i e s and i n d i v i d u a l s . H o w e v e r , U pper P e n i n s u l a t r e m b l i n g and b i g t o o t h a s p e n fam ilies p lanted i n s o u t h e r n Lower M i c h i g a n s t o p p e d g r o w t h 108 109 earlier t h a n Lower P e n i n s u l a f a m i l i e s b e c a u s e o f e c o t y p i c d ifferen ces asso ciated w ith p h o to p erio d These e c o ty p e d i f f e r e n c e s in teractio n ) (genotype x e n v iro n m e n t betw een p l a n t i n g th e geographic d is ta n c e s and t e m p e r a t u r e . sites s h o u ld be c o n s id e r e d are g re a te r than 325 km. A d d i t i v e g e n e t i c v a r i a n c e was f o u n d f o r h e i g h t , an d o t h e r g r o w t h - r e l a t e d M ating d e s i g n s (ie ., tra its volum e, in th e asp en progeny t e s t . N o r t h C a r o l i n a D e s i g n 2) t h a t i d e n t i f y a d d i t i v e e f f e c t s w ould be u s e f u l in h eritan ce p a tte rn s. was f o u n d if and f u r t h e r c l a r i f y M ost n o n - a d d i t i v e g e n e t i c v a r i a n c e in m o rp h o lo g ic a l tra its. H y b r i d i z a t i o n o f P. t r e m u l o i d e s an d P. g r a n d i d e n t a t a d i d n o t p r o d u c e h e t e r o t i c progeny e x c e p t in th e h y d ro p o n ic system . h y b rid iza tio n stu d ies on s e l e c t i n g g en etic F uture s p e c ie s in th e asp en s s h o u ld f i r s t c o n c e n t r a t e p a r e n t s w i t h good co m b in in g a b i l i t y variance) for i m p o r ta n t economic t r a i t s im plem enting th e h y b r i d i z a t i o n (ad d itiv e before phase. The p h o t o s y n t h e s i s an d h y d r o p o n i c s t u d i e s in dicated t h a t t h e g ro w th p e r f o r m a n c e o f t h e h y b r i d s r a n g e d from average t o s u p e r i o r when c o m p a r e d w i t h t h e p a r e n t s p e c i e s . The f i e l d b etter aspen. s t u d i e s , h o w e v e r , showed t h a t m o s t h y b r i d s w e r e no than in term ed iate These e a r l y in grow th t o resu lts t r e m b l i n g and b i g t o o t h s u g g e s t t h a t P. X s m i t h i i d o e s n o t prom ise to be a c o m m e rc ia lly v a l u a b l e h y b rid . In co n trast, (P. t h e grow th p e rfo rm a n c e of th e trih y b rid X r o u l e a u i a n a X P. t r e m u l o i d e s ) and u n p u b l i s h e d d a t a o f t h e P. Xr o u l e a u i a n a h y b r i d stro n g ly suggest th a t these 1 10 h y b r id s s h o u ld be em phasized stu d ies. in f u t u r e h y b r i d i z a t i o n To d e v e l o p a b r e e d i n g p r o g r a m u s i n g more g e rm p la s m o f b o t h P o p u l u s a l b a these h y b rid s, and P. g r a n d i d e n t a t a is n e c e s s a ry because o f th e r e l a t i v e l y narrow g e n e tic b ase fo r both s p e c ie s in t h e c u r r e n t p ro g e n y t e s t s . c o n t r o l l e d m a tin g s betw een s e l e c t e d In a d d i t i o n , f a m ilie s of trem b lin g a sp e n s h o u ld be i n i t i a t e d b e c a u s e o f t h e e x c e l l e n t g row th o f t h i s s p e c i e s in a l l p lan tatio n s. A tre m b lin g aspen im provem ent program w ould be p a r t i c u l a r l y u s e f u l for s it e s t h a t a r e e c o l o g i c a l l y u n s u i t a b l e f o r P. X r o u l e a u i a n a hybrids. The q u a n t i t y o f g e n e t i c v a r i a t i o n , co n tro lled p o llin a tio n s , the ease of and t h e i n h e r e n t e a r l y f l o w e r i n g in t h e a s p e n s p r o v i d e am ple mechanisms f o r p r o d u c in g g en etically -im p ro v ed sp ecies. seed so o n e r th a n m ost M ichigan t r e e