THESIS OVERDUE FINES ARE 25¢ PER DAY PER ITEM Return to book drop to remove this checkout from your record. ”AR 3" Z? 1‘35“" if???”— __' 2‘12! "En-h" .Jr- ' 4W III! I Immnmmfilmllnfimmfiu ;, ' 3 1293 00660 8313 OVERDUE FINES ARE 25¢ PER DAY PER ITEM Return to book drop to remove this checkout from your record. :IQW 113'9g2‘ f ‘ 09'? MAR 7 Z; 199‘: i377”); _ 2")“ 'u. ‘5‘- .Ir- ‘ O SEED SOURCE VARIATION AND GROWTH CONTROL OF SUGAR MAPLE (Acer saccharum Marsh.) SEEDLINGS BY Bruce Wade Wood A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Forestry 1979 ABSTRACT SEED SOURCE VARIATION AND GROWTH CONTROL OF SUGAR MAPLE (Acer saccharum Marsh.) SEEDLINGS BY Bruce Wade Wood Sugar maple (Acer saccharum Marsh.) seedlings grow slowly in the natural environment. Height growth occurs for about 8 weeks, then a resting bud is formed that will generally remain dormant until exposed to about 2000 hours of chilling. This slow and determinate growth characteristic presents a formidable barrier to forest geneticists who want to genetically evaluate seed sources and to commercial nurserymen who desire high quality seedlings in a relatively short time. Accelerated-optimal- growth (AOG) is a concept in tree production which combines containerized greenhouse production with control of growth and development by regulating factors which primarily affect tree growth. If the application of these factors to sugar maple could produce greater growth during the normal growing period and/or override the determinate growth characteristic and allow continuous growth, then it would be advantageous to researchers and nurserymen Bruce Wade Wood concerned with growing sugar maple. For these reasons various methods for regulating growth of sugar maple were studied. Results showed that seedlings grown in a green- house under continuous light (AOG) were much taller than seedlings produced in the outdoor nursery, even though they were grown for equal periods of time under identical natural daylight photOperiods. Seed source differences were detectable for AOG seedlings after 4 and 16 months from germination but only after 16 months for those grown in the nursery. Differences in several growth variables between peninsulas and correlation of 16-month AOG results with environmental factors indicate the existence of dif- ferent races between the Upper and Lower Peninsulas of Michigan. This conclusion was further supported by seed morphology. Based on AOG results, Upper Peninsula trees grow much smaller than those from the Lower Peninsula and Eastern Upper Peninsula trees grow taller than Western Upper Peninsula trees. If these patterns exist after AOG and nursery seedlings have been grown in common environ- ments for several years, then the AOG system would have considerably reduced the time required for genetic evalu— ation. Sugar maple growth and develOpment during the normal growth period were accelerated or otherwise con— trolled by carbon dioxide fertilization, temperature, Bruce Wade Wood and exogenous foliar applications of gibberellic acid (GA3)’ GA7, A4+7, and benzyladenine (BA). Applied GAS and BA affect height growth, component dry weights, total dry weight, leaf area, and rootzshoot ratio. 6A7 also affected root growth. The determinate growth nature of maple can be overridden and the growth apparently extended indefinitely by growing seedlings under continuous light and treating the resting bud with either GA or 6A3 or by 7 complete defoliation of the seedling. Budbreak response to bud applications of GA or 6A3 is dependent upon time 7 since budset. GAs were only effective when applied during about 2 months after budset. Defoliation treatments were effective up to at least 6 months after budset. Relatively low temperature (20° C vs 30° C) growing conditions par- tially prevented the cessation of determinate growth. Triacontanol, a recently discovered growth regu- lator, had no affect on growth of sugar maple. The photosynthetic and respiratory mechanisms of seedlings grown in either a constant CO2 concentration or varying temperature regimes became adapted to those growth conditions. The temperature-adapted mechanisms readapt to different temperatures after 1 month. COz-adapted seedlings were not able to readapt to lower C02 levels after 2 weeks of exposure at the lower levels. Transfer of seedlings adapted to CO2 or temperature levels to a lower CO2 concentration or different temperature environ- ments greatly decreases net photosynthesis. Bruce Wade Wood Carbon exchange rates of seedlings decreased as the seedlings aged and entered dormancy, with peaks in photosynthesis immediately after budset. At 32 weeks after germination, dark respiration exceeded net photo- synthesis. There were no differences in rates among leaf types of similar chronologic age. ACKNOWLEDGMENT S I wish to express my sincere appreciation to Dr. James W. Hanover, Chairman, for his assistance, support, and suggestions which made this study possible. My sincere gratitude goes to Dr. F. G. Dennis for his excellent advice and review, and to Drs. D. I. Dickmann and B. Hart for their essential contributions. Finally, I thank my wife, Kathryn, for her encouragement and much appreciated assistance. ii TABLE OF CONTENTS LIST OF TABLES . . . . . . . . . . . . LIST OF FIGURES . . . . . . . . . . . INTRODUCTION. . . . . . . . . . . . . Chapter I. ACCELERATED GROWTH FOR EARLY GENETIC EVALU— ATION OF SUGAR MAPLE . . . . . . . Abstract . . . . . . . . . . . Introduction. . . . . . . . . Materials and Methods. . . . . . . II. III. Iv. Results and Discussion . . . SUGAR MAPLE SEEDLING GROWTH. . Abstract . . . . . . . . Introduction. . . . . Materials and Methods. . . . Results and Discussion . . . HYDROPONIC SYSTEM FOR STUDYING ROOT GROWTH OF SUGAR MAPLE SEEDLINGS Abstract . . . . . . . . Introduction. . . . . Materials and Methods. . . . Results and Discussion . . . LACK OF EFFECT OF TRIACONTANOL ON SUGAR MAPLE SEEDLINGS. . . . Abstract . . . . . . . . Introduction. . . . . . Materials and Methods. . . . Results and Discussion . . . iii GROWTH-REGULATING CHEMICALS FOR ACCELERATING Page vii A OO‘U‘lnb 27 28 30 32 59 59 59 61 65 Chapter V. CARBON DIOXIDE, TEMPERATURE, AND AGE EFFECTS ON GROWTH, PHOTOSYNTHESIS, AND DARK RESPIRATION OF SUGAR MAPLE SEEDLINGS Abstract . . . . . . . . . Introduction . . . . . . . . Materials and Method . . . . . Results and Discussion. . . . . SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS . BIBLIOGRAPHY . . . . . . . . . . . iv Page 86 86 87 89 94 119 128 CHAPTER Table 1. CHAPTER Table 1. LIST OF TABLES I Effect of three production methods on mean growth of half-sib sugar maple progeny . Correlation coefficients between growth characteristics at 4 months of age with those at 16 months for sugar maple seed- lings grown by the AOG method . . . . Growth characteristics of sugar maple seedlings from various seed sources in Michigan's Upper and Lower Peninsulas . Correlation of characteristics of 16- month-old sugar maple seedlings grown under AOG with environmental variables at the seed source. . . . . . . . Climatic variables at seed source locations. . . . . . . . . . . Comparisons of characteristics of sugar maple seed collected from parents grow- ing in Michigan's Upper and Lower Penin- sulas . . . . . . . . . . . . Correlations between characteristics of sugar maple seed collected from parents growing in Michigan's Upper and Lower Peninsulas and several source variables. II Effects of defoliation and hormone appli- cations to buds on budbreak in sugar maple seedlings experiencing budset for different periods of time . . . . . Page 11 15 16 19 20 22 24 53 Table CHAPTER Table 1. CHAPTER Table 1. CHAPTER Table l. 2. Page The effects of defoliation and application of GA7 and GA3 to buds on growth follow— ing budbreak . . . . . . . . . . 55 Effects of degree of defoliation on bud- break of sugar maple seedlings . . . . 58 III Effects of photoperiod and gibberellin A7 treatments on root and shoot growth of sugar maple seedlings grown in an irrigation-type hydroponic system . . . 78 IV Growth responses of sugar maple seedlings to foliar applications of triacontanol . 84 V Effects of carbon dioxide levels on growth of sugar maple seedlings . . . . . . 95 Effects of temperature on growth of sugar maple seedlings . . . . . . . . . 100 vi LIST OF FIGURES CHAPTER I Page Figure 1. Location of the areas in Michigan from which sugar maple seeds were collected. Numbers refer to climatic data found in Table 5 . . . . . . . . . 2. Sixteen-month-old sugar maple seedlings grown for 2 periods of 4% months each under 2 cultural methods. Seedlings on the left were grown in plant bands in an outdoor nursery, while those on the right were grown in plant bands under accelerated-optimal-growth (AOG) con- ditions. Seedlings represent the tallest of the 2 treatments . . . . . 13 CHAPTER II Figure l. Defoliation treatments used to determine effects of defoliation on budbreak of sugar maple seedlings. Vertical line represents seedling stem and horizontal lines represent leaves remaining after pruning. . . . . . . . . . . . 34 2. Growth response of sugar maple seedlings to hormone and photoperiodic treatments. Vertical lines equal the standard error of the mean . . . . . . . . . . 36 3. Effects of hormone and photOperiod treat- ments on total dry weight accumulation of sugar maple seedlings. Vertical lines equal the standard error of the mean. . . . . . . . . . . . . 38 vii Figure Page 4. Dry weight distribution of sugar maple seedlings treated with various hormones and photoperiods. (A) Gibberellin A4+7 (B) Gibberellin A3 (C) N-6-Benzy1ade- nine. Photoperiods consist of natural and continuous consisting of natural plus fluorescent light during the natural dark period. Vertical lines equal the standard error of the mean . . 41 5. Effects of various hormone and photoperiod treatments on the root:shoot ratio of sugar maple seedlings. Vertical lines equal the standard error of the mean . . 43 6. Comparisons between GA7 and GA3 with respect to height increase and dry weight of sugar maple seedlings. Vertical lines equal the standard error of the mean . . . . . . . . 46 7. Component dry weights and root:shoot ratio of sugar maple seedlings treated with GA7 and GA3. Vertical lines equal the standard error of the mean . . . . . 49 8. Relative effects of GA7 and GA3 treatments on total leaf area and leaf number of sugar maple seedlings. Vertical lines equal the standard error of the mean . . 51 CHAPTER I I I Figure l. A hydroponic system for growing forest tree seedlings for root observation . . 63 2. Comparison of root development of sugar maple seedlings grown 3 months in paper plant containers containing an artificial soil mix, 3 months in an irrigation-type hydroponic system, and 1 year in an outdoor nursery . . . 67 viii Figure 3. Root and shoot growth rates of sugar maple seedlings grown under a natural photo- period in a hydroponic system. Week 0 = January 24. Vertical lines equal the standard error of the mean. Primary root equals tap root. Secondary roots refers to the 6 longest secondary roots . 4. Cumulative root number and ratio of ter- tiary to secondary roots in sugar maple seedlings grown under a natural photo- period in a hydroponic system. Week 0 = January 24. Vertical lines equal the standard error of the mean . . . . . 5. Cumulative root growth (tap root and 6 longest secondary roots) of sugar maple seedlings grown under 2 photoperiods (natural vs. continuous with supplemen- tal fluorescent light during the normal dark period) and 2 gibberellin A7 (0 ppm vs. 200 ppm as a foliar spray at biweekly intervals) treatments. Week 0 = Jan- uary 24. Vertical lines equal the standard error of the mean . . . . . CHAPTER V Figure l. The effects of carbon dioxide concentration on net photosynthesis and dark respira- tion of sugar maple seedlings precondi- tioned in 700, 1400, and 2100 ppm carbon dioxide atmospheres. Vertical lines equal the standard error of the mean . . 2. Effects of cool and warm temperatures on net photosynthesis of sugar maple seedlings grown in constant cool or warm environments. Vertical lines equal the standard error of the mean . . . . 3. Effects of cool and warm temperatures on dark respiration of sugar maple seed- lings grown in constant cool or warm environments. Vertical lines equal the standard error of the mean . . . . . ix Page 70 75 80 97 104 106 Figure 4. Changes in net photosynthesis and dark respiration with development of greenhouse-grown sugar maple seedlings with 1 leaf node. The states of development are as follows: (A) leaves 1/3 expanded, (B) leaves 2/3 expanded, (C) leaves fully expanded and has set bud, (D) time of budbreak on trees with 2 or 3 nodes, (E) time of second budset for trees with 2 and 3 nodes. Vertical lines equal the standard error of the mean . . . . . . . . . . . . 5. Changes in net photosynthesis and dark respiration with develoPment of green- house-grown sugar maple seedlings with 2 leaf nodes. The states of development are as follows: (A) leaves 1/3 expanded, (B) leaves 2/3 expanded, (C) leaves fully expanded and has set bud, (D) time of budbreak on trees with 2 or 3 nodes, (E) time of second budset for trees with 2 and 3 nodes. Vertical lines equal the standard error of the mean. . . . . 6. Changes in net photosynthesis and dark respiration with development of green- house-grown sugar maple seedlings with 3 leaf nodes. The states of develOpment are as follows: (A) leaves 1/3 expanded, (B) leaves 2/3 expanded, (C) leaves fully expanded and has set bud, (D) time of budbreak on trees with 2 or 3 nodes, (E) time of second budset for trees with 2 or 3 nodes. Vertical lines equal the standard error of the mean. . . . . Page 111 113 115 INTRODUCTION Sugar maple (Acer saccharum Marsh.) is a North American tree species native to the United States and Canada. Its natural range extends over most of the Eastern United States and Southeastern Canada. It is one of the largest and most important hardwoods within its range and is most valuable for its beautiful wood, maple syrup and sugar source, shade tree, and aesthetic qualities (Fowells 1965). The importance of these qualities makes genetic improvement of sugar maple a worthwhile undertaking. However, the relatively slow growth and determinate growth habit of sugar maple seedlings make genetic improvement a very slow process with useful information coming many years into the future. This limitation has hindered the accumulation of information about the amounts and geographic distribution of variation. 5) Sugar maple is a particularly difficult species to induce to grow continuously. It generally grows for only about 8 weeks and sets a resting bud that will remain dormant until it has experienced about 2000 hours of chilling (Taylor and Dumbroff 1975). Seedlings express this response even when grown in protective greenhouse environments where there is no apparent stress situation. This presents significant problems for the tree geneticist, breeder, and commercial nursery- man attempting to study or grow sugar maple. This problem is not unique for sugar maple but is also encountered with other valuable hardwood species. Thus, information acquired about its growth control can likely be applied to many other species. One way of obtaining both earlier genetic evalu- ation and larger seedlings in a shorter period of time is to implement cultural practices that offer the greatest potential for increasing growth and development. Accel- erated-optimal-growth (AOG) is a relatively recent growth concept that applies such cultural practices to produce larger and more vigorous seedlings in a shorter period of time. It incorporates various natural and artificial factors of the growth environment into a system that provides for programmed tree growth (Hanover 1972, 1976, 1977; Logan and Pollard 1976). Before growth and development of sugar maple seedlings can be successfully accelerated and otherwise regulated, it is necessary to determine how they are affected by various cultural practices during different develOpmental states. The main objective of this study was to investigate the effects of growth-stimulating factors on growth during both the grand period of growth, i.e., the period of growth and development from bud break to terminal bud formation, and the inductive phase, i.e., the period of cessation of growth during which growth and development may resume under suitable conditions (Samish 1954; Vegis 1964). A second objective was to gain a better understanding of the utility of these fac- tors for genetic evaluation and commercial seedling pro- duction. CHAPTER I ACCELERATED GROWTH FOR EARLY GENETIC EVALUATION OF SUGAR MAPLE Abstract A method is described for accelerating juvenile growth and development of sugar maple (Acer saccharum Marsh.) seedlings for early progeny and provenance evalu- ation and plantation establishment. Outdoor nursery treatments revealed few seedlot differences and no provenance differences at 4 and 16 months of age. In contrast, accelerated seedlings exhibited pronounced seedlot and provenance differences at both ages. Accel- erated trees had a 29 and 80% height superiority at 4 and 16 months, respectively. This was due to increased number of nodes and internode length, rather than more growth flushes. Provenance differences in height, date of bud- break, number of nodes, and growth flushes revealed by the accelerated treatment and supplemented by seed char- acteristics indicate existence of Upper and Lower Penin- sula races in Michigan. If long-term observations and correlative analyses of both nursery and accelerated treatments support these provenance and peninsula dif- ferences, then accelerated growth can considerably shorten the time required for genotypic evaluation of sugar maple. Introduction Forest tree seedlings used for genetic testing are often produced in outdoor nurseries. Such seedlings are often characterized by slow growth rates and may pro- duce trees of poor quality for establishing genetic plantings. This means that the investigator must either wait several years before seedlings can be planted in test plantations or establish plantations with small and poor quality trees that are susceptible to stress and competition. Assuming trees of acceptable quality are produced, several years must generally elapse before reliable genetic variation patterns can be discerned. Consequently, forest geneticists need methods that accelerate the identification of superior genotypes. The accelerated-optimal-growth (AOG) concept is a prac- tical method that may partially overcome the time limi- tations imposed by traditional methods and thereby better control seedlings' size and quality and perhaps reduce the time required to identify superior genotypes. AOG is based upon the programmed control of growth by the use of light, temperature, mineral nutrients, water, carbon dioxide, growth-regulating chemicals, container dimensions, etc. (Hanover, 1977, 1976; Hanover et a1. 1976). Applying the AOG concept to greenhouse production of containerized seedlings allows the investigator increased control over growth, development, and physio- logical status of seedlings. Thus, seedlings can be produced in a few months rather than years. A potential problem with the use of the AOG concept or greenhouse culture for accelerating tree improvement is the effect of growth control factors on either short- or long-term changes in seed source ranking (Faulkner 1967). The objectives of this study were: (a) to determine if such rank changes occur in sugar maple (Acer saccharum Marsh.), (b) to compare the magnitude of growth of AOG and nursery- produced seedlings, and (c) to investigate the use of AOG for use in making genetic evaluations. Materials and Methods Sugar maple seeds from 12 geographic areas were collected in Michigan's Upper and northern Lower Penin- sulas (Figure 1). Three to 10 individual trees were collected from each area for a total of 91 seedlots. Seedlots were kept separate by individual parents for establishment of a half sib-progeny test. When possible, seeds were collected from trees which were average or FIGURE 1. Location of the areas in Michigan from which sugar maple seeds were collected. Numbers refer to climatic data found in Table 5. better than others in the stand in form and height. Otherwise, selections were from accessible trees with sufficient seed. Seeds were air-dried at room temperature to 30% moisture. Seed width, wing width, wing length, and wing angle were measured on random samples from each seedlot. Before sowing, the seeds were stratified 4 months in moist perlite at 3° C. Seeds were then sown in plastic cases containing 5 X 5 X 28 cm polycoated paperboard plant bands filled with a 1:1:1 peat—perlite-topsoil potting mix. Those sown directly in the nursery soil were also spaced at 5 X 5 cm. The experimental design consisted of 6 trees of each seedlot in each of 3 blocks in each of 3 growth environments. The 3 growth treatments consisted of seedlings grown in the ground in the outdoor nursery and in plantbands in both the outdoor nursery and greenhouse. Greenhouse-grown seedlings were exposed to continuous light with the normal dark period being replaced by supplemental light from fluorescent tubes producing 50 chm-Zs-l at plant level. Moisture and nutrient element levels were maintained near optimum. Trees were grown in their respective environment for 16 months (including a leafless dormancy interruption of 5 months). After the first frost all trees were exposed to natural photoperiod and temperatures. Shortly after budbreak the AOG trees were again exposed to 10 continuous light and warm temperatures in the greenhouse environment. Therefore, length of growing season was essentially identical for the greenhouse and nursery treatments. At the end of the growth periods, measure- ments were made of height, budbreak, internode length, node number, and number of growth flushes. Results and Discussion Production Methods After all treatments had grown 4 months (first growing season) AOG seedlings were 29% taller than those grown outside (Table 1). There was no difference between the outdoor nursery treatments. By the end of the first growing season, nursery grown trees exhibited few seedlot differences and no provenance differences. However, it was possible to discern pronounced seedlot and provenance differences in AOG trees. After the second season, AOG trees were 80% taller than nursery trees (Table 1, Figure 2). Thus, AOG trees not only maintained their height superiority but increased it at an accelerated rate. Again, after 16 months there was no height dif- ference between nursery treatments. After 16 months AOG seedlings averaged 24 to 40% more nodes and averaged internode lengths 29 to 44% greater than nursery treat- ments. However, there was no increase in the number of flushes in the AOG trees (Table 1). 11 .£w3oumlamfiaumonpmumuoamoo¢~ .umoa omcom OHQHDHDS m.cmocsa an wuflaflnmnoum mo Ho>oH wm on» an umnuocm oco Eoum ucmumwmaw waucm0flwwcmflm uo: mum umuuma meow may ha bosoHHOM mosHo> .mcEsHoo cwnuwza n H.m o N.H n H.m n o.m~ a o.oa ~00< m m.m m N.H m m.m m o.vH m m.> Ampcon unwamv hummusz m m.m m H.H m m.m o n.ma Ho v.n Apcsoumv hummusz So umnEsz Honesz 80 So .OE ma .OE ma .05 ea .08 ma .08 v pocumz coauosooum cumcmq mwocumucH monmsam mmwoz unmwom .mcmmoum magma ummsm nflmuwamn mo nuzoum some so mwonumfi cofluospoum mounu mo powwmm .H mqmde FIGURE 2 . 12 Sixteen-month-old sugar maple seedlings grown for 2 periods of 4% months each under 2 cul- tural methods. Seedlings on the left were grown in plant bands in an outdoor nursery, while those on the right were grown in plant bands under accelerated-optimal-growth (AOG) conditions. Seedlings represent the tallest of the 2 treatments. 13 FIGURE 2 14 Second season growth characteristics of AOG trees were significantly correlated with first season characteristics only for the following variables (second season characteristics given first): height vs. height, flush number vs. height, node number vs. node number (Table 2). Although statistically significant, all cor- relations were low. The low correlation between first and second season height for AOG seedlings suggests that subtle environmental interactions are taking place or genotype expression changes with age. Thus, prediction of second season height or any other measured growth characteristic based upon first season height or number of nodes does not appear to be feasible. Statistical comparison of growth characteristics for nursery-grown trees revealed a few seedlot differences but no provenance or peninsular differences (Table 3). In contrast, AOG trees exhibited seedlot, provenance, and peninsular differences in height, but not in node number or number of flushes. Since there were few seed- lot differences in the nursery-grown treatments, it was not possible to determine the influence of the treatments on the change in seedlot ranking. Variation Patterns t. LP seedlings were 10% taller than UP seedlings after one season and 29% taller after two. Second season heights of trees from the eastern UP averaged 15 TABLE 2. Correlation coefficients between growth charac- teristics at 4 months of age with those at 16 months for sugar maple seedlings grown by the A061 method. Characteristics Characteristics at 16 Months2 at 4 Months Height gIfigfizs Egggzr Nodes/Flush ................... r-—-—---------------- Height 0.36** 0.40** 0.20 0.18 Number nodes 0.12 0.22 0.47** 0.17 1Accelerated—optimal-growth. de = 82. ** Significant at the 1% level. 16 .Ho>OH mm osu um DCOHOMMAc >Hucmowmacmflm uoc mum mcfisaoo mmo:u :fi mosam> m .Hw>ma mm on» um ucwumwwwp >Hucm0flmwcmflm uoc who umuuma meow mnu xn co3oHaom mammE .mCOmHHomEoo :mHSmcflcmm cwnuw3= cam :mmHDmcficmm :mm3uwfl: :wnuws 0cm mcESHoo aficufiz m .mHsmcficom Hm3oqv .mafimcflcwm membm .ouflm Hangman mo mcomfiummeoo How umounu mucovsum m:flm5 mammamcm HMOfiumflumumm .mpcmn Hanan ca czoum mmcflanomma N.H v.m vH w N.H m.m 0 on m HH O «N ma cumummz N.H v.~ vH m ~.H w.m 0 HM m HA m ma van :uwcuuoz N.H m.N vH m N.H N.m 9 mm m 0H a an m: cumummm N.H m.N vH m N.H m.m m mm o m m ma mm: cuoumwz moanmCHcmm cflnuw3 N.H v.m vH m N.H o.m n Hm n Ha Q Hm oHsmcacom hosoq . . . . m m m m DmCHcom Momma mm H mm m ova mm mm a 0H m vm OH ma H mmHsmcficwm cmw3umm Hmnfisz umnEdz Eu EU monasz HOQEDZ Eu EU mwma .08 .08 .08 .05 .0E .08 .08 .06 .05 ca um ma as ea um v um ma um ma um 0H um v um ma um cmsHm opoz ucmflom unmflmm nmsam mcoz ucmfimm unmwom xmounpsm mmCOmfiummfiou H>uwmusz nuzouolHmEflumolcoumuoHoood oounom oomm .mmHSmCHcom Hm3oq 0cm Momma w.comw£ofiz :fl moousom comm mDOHum> Eouw mmcwapomm manna woman mo moflumfluouomumco su3ouw .m mqmdfi 17 11% taller than their western counterparts, while those from the northern LP averaged 24% taller than those from the eastern UP. There was no difference between northern LP and western LP sources. Northern UP sources were 41% taller than western UP sources at 16 months. These height differences were due to differences in internode length since the number of flushes or nodes did not differ with provenance (Table 3). Thus there was no provenance- photoperiod interaction with respect to flush or node number. Budbreak of UP trees was earlier than LP trees. Those from the western UP broke bud 3 days earlier than those from the eastern UP. Seedlings from the northern LP broke bud earlier than those of either the eastern UP or western LP. This observation suggests that northern LP trees may be well adapted for growth in the western UP. Since their growth is greater than those from the western UP, it may be advantageous to use northern LP trees in the western UP when establishing sugar maple plantings in the western UP. Differences in progeny height growth between the two peninsulas and between the eastern and western UP are important to anyone handling seed or seed— lings from these sources. The differences in height growth and consequently volume could conceivably affect lumber or fiber yields, assuming the trend holds true for the adult trees. 18 Height at 16 months was positively correlated with growing season, and with mean annual and mean January temperatures, and negatively correlated with latitude (Table 4). The actual climatic conditions at the locations of the seed sources are presented in Table 5. Mean annual temperature and growing season accounted for 82 and 58%, respectively, of the variation in height growth. These correlations suggest that height growth is an adaption to the temperature and length of growing season under which the parent trees have evolved and is of selective advantage in these environments. Obviously, seedlings which are defoliated prematurely by frost and then reflush or which fail to harden pr0perly will have a lesser chance of survival than seedlings which grow rapidly but cease growth before damaging frost. The number of flushes, number of nodes, and nodes per flush were not correlated with any source variable (Table 4). Source also affected budbreak with UP seedlings breaking bud an average of 4 days earlier than those from the LP. Budbreak in northern LP trees was earlier than in those from the eastern UP. Western LP trees were much later than any other source. Surprisingly, date of budbreak was not correlated with growing season. How- ever, it was correlated with mean annual temperature and negatively correlated with latitude (Tables 4 and 5). Eighty-two percent of the variation in budbreak could be l9 .suflaflhmnoua mo Hm>wa Am man an pamoflmflcmflm a. .UDQ mxoun mcflawmmm umuwm ms» wumo may mm3 ucwEwHSmme mo mmmmH ac. mo. so. «mm. mm. m Aoov musumumosmu humsamb com: «H. OH. OH. no. me. m Aoov musumummfiou wash :mmz Ha. ma. mo. «om. «Hm. m Aoov muoumummfimu Hmsccm cmmz mm.- so.s HH.- .56.- .mm.. OH 1mmmummoc waspflumq mw.u Hm. AH. .ms. mm. m Imsmcc commmm mafizoum mo numcmq llllllllllllllllllllllllll HllllllllIlllllllllllllllll zmsam mmooz mmnmsam mnucoz xmmunpzm Mom m0 m0 ma um mo mp moanmwum> mousom mwpoz HonEsz umnEsz unmwom Hmuoo .oousom boom may no moanmaum> Housmacouw>co spas wo< Hops: csoum mmcflaommm mHQmE Homsm paonnucoaloa mo moflumflumuoonmno mo coflumamuuoo .v mqmmpv :Ommom oca3oum mo numcma Na aa ca 0 m h o m v m N a oasmcacmm Hosea maswcacom uw3oa maDmCacom momma masmcacmm Momma :uoumoz cuonuuoz cuoummm cuoumoz moanmaum> Oaumfiaao WCOH#MUQH OUHDOW mywmvm .mcoauMUOa oUHDOm noon um moaQMaum> oaumfiaau .m mamdfi 21 attributed to mean annual temperature. The correlation coefficient between length of growing season and mean annual temperature was 0.93. The lack of correlation of budbreak with growing season may be partially due to limited numbers of observations. Trees evolving in areas of high mean annual temperature are probably exposed to a relatively long and warm growing season. This suggests that early flushing of buds is characteristic of trees from environments where mean annual temperature is low. Seedlings adapted to regions with short growing seasons tend to flush early and, thus, capitalize on suitable growing conditions. The observation that UP trees broke bud 4 days earlier than those from the LP suggests that this is an important long-term survival mechanism, espe- cially when they are naturally relatively slow growing due to the probable trade-off of growth rate for cold hardiness. Certain sugar maple seed characteristics also exhibit within and between peninsula differences (Table 6). Seeds collected from the UP had wings closer together, and with greater wing length and width than LP seedlings from the western LP. Those from the western UP had smaller wing angles but shorter wing length and width than those from the eastern UP. Sources from the northern LP had a greater wing angle and smaller wing width than those from the western LP. Seed width did not differ with sources (Table 6). 22 TABLE 6. Comparisons of characteristics of sugar maple seed collected from parents growing in Michigan's Upper and Lower Peninsulas. Seed Characteristics Seed Source Comparisonsl Wing Wing Wing Seed Angle Length Width Width Degrees mm mm mm Between Peninsulas Upper Peninsula 17 b2 22 b 9 b 16 a Lower Peninsula 24 a 19 a 7 a 15 a Within Peninsulas Western UP3 13 c 22 b 8 c 16 a Eastern UP 4 21 b 30 c 9 d 15 a Northern LP 19 b 20 ab 7 b 15 a Western LP 32 a 18 a 6 a 15 a 1Statistical analysis using Student's t-test for comparisons of unequal size. 2Within columns and within "between peninsula" and "within peninsula" comparisons, means followed by the same letter are not significantly different at the 5% level of probability. 3Upper Peninsula 4Lower Peninsula 23 Seed characteristics were correlated with environ- mental variables (Table 7). Wing angle was not signifi- cantly correlated with any parameter, though within and between peninsula differences were evident. Wing length and width were strongly correlated (negatively) with mean July temperature, which accounted for 97 and 81% of the variation in wing length and width, respectively. Thus, high temperatures during seed development may cause a reduction in length and width of the wings. Mean July temperature was not associated with differences in seed width or wing angle, and no seed characteristic was cor- related with growing season or mean annual temperature. These patterns of variation show no clear adaptive advan— tage of the seed characteristics with respect to their source environments. The contrast between growth and seed character- istics of parents and seedlings from Michigan's two penin- sulas suggests the existence of different races of sugar maple. Similar results have been observed by Wright (1972) for several conifer species. He reasoned that the peninsula differences are due primarily to differences in climatic selection pressures and the range gap between peninsulas. The UP has generally lower seasonal temper- atures, shorter growing season, and different photoperiods. These factors may act individually or interact in a subtle manner such that they effect the fitness of sugar [5 24 TABLE 7. Correlations between characteristics of sugar maple seed collected from parents growing in Michigan's Upper and Lower Peninsulas and several source variables. Seed Characteristics Source Variables df Wing Wing Wing Seed Angle Length Width Width Degrees mm mm mm ---------------- r---————-—-————-— Length of growing season (days) 5 -.32 -.47 -.53 -.73 Latitude (degrees) 10 .24 .78** .46 .69** Mean annual temperature (°C) 3 -.71 -.81 -.78 -.87 Mean July temperature (°C) 3 -.68 -.98** -.90* -.48 Mean January temperature (°C) 5 -.09 .76* -.73 -.86* */** Significant at 5 and 1% levels, respectively. 25 maple. This difference in selection pressure has been operating since the glaciers retreated from the region. Consequently, trees in the UP should be more cold hardy than those in the LP. Because cold hardiness and growth rate are generally negatively correlated, UP trees might be expected to grow more slowly. This was indeed what was observed. Perhaps this accounts for the observation of less growth and earlier budbreak for western UP vs. eastern UP and UP vs. LP trees. The range gap between the two peninsulas created by the Straits of Mackinac is about 4 miles from the tree line on each peninsula. Since sugar maple is primarily bee pollinated (Kirbel and Gabriel 1969), the vast majority of sugar maple seed falls within a relatively short distance of the source (Wright 1976). Gene flow is greatly inhibited by this small range gap. The only natural avenues open for gene flow from the LP into the UP are around Lake Michigan via Wisconsin and around Lake Huron via Ontario. Both routes are several hundred miles long. Thus, distance in a continuous range can also act as an isolating mechanism. The combination of distance, range gap, and different selection pressures may have facilitated the development of distinct races between the two peninsulas. When the observation of peninsula differences in growth characteristics, correlation of these growth 26 characteristics with environmental factors at the source of origin, seed differences between peninsulas, dif- ferences in selection pressure, and the barrier to gene flow are evaluated collectively, then there seems to be good evidence that distinct races exist between peninsulas. This will be determined by evaluation of AOG and nursery- produced seedlings upon outplanting. If confirmed, then the use of AOG for early genetic evaluation would have considerably reduced the time required to make meaningful genetic evaluations. This study provides evidence that it is possible to extract meaningful and representative genetic information from certain provenance or progeny test grown for a relatively short time under growth accelerating conditions. Consequently, accelerated growth techniques seem to have potential as tools for early gene- tic evaluations of forest tree species. CHAPTER II GROWTH-REGULATING CHEMICALS FOR ACCELERATING SUGAR MAPLE SEEDLING GROWTH Abstract The possibility that growth regulators might be used to accelerate and/or manipulate growth and develop- ment of sugar maple (Acer saccharum Marsh.) was investi- gated. Repeated foliar sprays of gibberellins (GA3, GA4+7, GA7) greatly increased stem elongation at all concentrations and slightly increased total dry weight at low concentrations. They increased internode length and leaf numbers and reduced root growth, thereby decreas— ing the root:shoot ratio. GA7 and GA4+7 were more effec- tive than was GA3. Benzyladenine (BA) increased dry weight of both root and shoot at low concentrations and inhibited stem elongation at all concentrations tested. At high concentrations, BA inhibited both root and shoot growth. The root:shoot ratio increased with increasing BA concentrations. Response to GA varied with seed source. Seedlings grew more under continuous light than under natural photoperiod. The GA growth effect was more pronounced under continuous light. 27 28 After 2 months of inactivity, resting buds were easily induced to grow by a single drOp of GA or GA 7 3 solution. BA had no effect on budbreak and indole-3- acetic acid (IAA) was only slightly effective. At 4 and 6 months no hormone treatment could induce budbreak, but complete defoliation was 100% effective at all three times. Leaving a single leaf on the seedling completely inhibited budbreak. The new growth produced after GA- induced budbreak consisted of more and longer internodes than did that after defoliation-induced budbreak. The results indicate that exogenous applications of BA and certain GAs provide a method for controlling growth and development of sugar maple seedlings. Introduction Accelerated-optimal-growth (AOG) is a relatively recent cultural system developed for controlling seedling growth by varying the environmental conditions in which a seedling is grown. These components may include light, temperature, mineral nutrients, carbon dioxide, growth- regulating chemicals, etc. (Hanover 1976, 1977; Hanover et a1. 1976). Incorporation of the AOG concept with greenhouse production of containerized seedling systems allows acceleration of growth and development of tree seedlings, resulting in a larger product in a much shorter period of time. Large seedlings can often be produced in months rather than years. 29 AOG implies use of a growing cycle that produces seedlings of desired size and physiological status for outplanting at a predetermined time. Before such a cycle can be efficiently and/or successfully implemented, it is important to know how to control height growth and espe- cially bud dormancy. Seedlings of several tree species exhibit a relatively strong determinate growth habit under AOG conditions. They typically exhibit one or two flushes of terminal growth followed by formation of a resting bud while environmental conditions are still favorable for continued growth. At this time, height growth will usually not resume until the resting bud has been exposed to a prolonged cold treatment. Sugar maple (Acer saccharum Marsh.) exhibits such behavior. Once it has formed a resting bud, approximately 2000 hours of cold chilling are required to induce budbreak. The ability to delay budset and thus produce large seedlings in a short period of time requires a knowledge of the factors regu- lating this determinate growth habit. One method of regulating meristematic activity is to apply growth regu- lators (Wareing and Phillips 1970). Our purpose was to determine if growth of sugar maple seedlings could be controlled by application of chemical growth regulators and/or by defoliation. 30 Materials and Methods Sugar maple seed for the following experiments were collected from Michigan sources and kept separate by seedlot. Seeds were air-dried at room temperature to about 30% moisture and stratified in moist perlite for 4 months at 3° C. {Germinated seedlings were sown in 5 X 5 X 28 cm polycoated paper plant bands contained in plastic cases and filled with a peat-topsoil (1:1) potting mix. Seedlings were grown in a greenhouse under natural daylight plus 100 chm-Zs-1 of continuous fluorescent light during the normal dark period, unless otherwise stated. Experiment 1. To investigate the potential for controlling growth with plant hormones, seedlings were treated at 12 weekly intervals with foliar sprays of GA3, a GA mixture (donated by Abbot Labs, Chicago; sample 4+7 was predominately GA7), or N-6—benzyladenine (BA). Growth regulators were dissolved in 95% ethanol and applied at 0, 150, 300, 600, and 1200 ppm in a water solution with 0.1% Tween-80. Seedlings were grown under both natural and continuous photOperiods to determine the effects of photoperiod and photoperiod-chemical interaction upon growth and budbreak. Treatments included 2 photOperiods, 3 hormones, and 5 concentrations of each hormone, and in a factorial arrangement of 30 treatments. Six trees of each of 5 seedlots were used per treatment. Hormone 31 treatments began 6 weeks after planting, and growth was recorded weekly for 12 weeks and dry weight was deter- mined at the end of 12 weeks. Experiment 2. To compare the effectiveness of GA3 and GA7 in accelerating growth, seedlings were sown in a randomized complete block design with 3 replicates of GA3 and GA7 were applied as 6 weekly foliar sprays at 0, 50, 100, 200, and 400 ppm in a water solution with 95% ethanol and 0.1% Tween-80 6 weeks after planting and at weekly intervals thereafter. Plot means were derived from measurements of 36 trees. At age 14 weeks, height, component dry weight, and leaf area were measured. Experiment 3. A third experiment was designed to determine if bud dormancy could be broken either by hormone application or defoliation and to determine if effectiveness varied with time of treatment. Experimental design was 4 randomized complete blocks of 11 treatments times 3 stages of development, using 24 trees per treat— ment per stage. Treatments were GA7, GA3, BA, IAA (0, 400, and 800 ppm), complete defoliation, and both ethanol-treated and nontreated controls. Hormones were dissolved in 95% ethanol and applied as a single drOp to the terminal bud. One-year-old seedlings were treated 2, 3, or 4 months after budset. Both time of budbreak and growth in height were recorded. 32 Experiment 4. To determine the degree to which leaves control budbreak, l-year-old trees with 3 foliated nodes, which had set buds 2 months earlier, were partially or wholly defoliated. Eight (Figure 1) defoliation treat- ments were applied in a randomized complete block design with 3 blocks. Six trees were used per treatment per block and budbreak was recorded. Results and Discussion Experiment 1. Effects of hormone treatment. Treatment of sugar maple with GA3 and GA4+7 greatly accelerated height growth, response increasing with increasing GA concentration for seedlings grown in both natural and continuous photoperiods (Figure 2). GA4+7 was generally more effective than GA3. In contrast, BA inhibited growth slightly, as previously reported (Fox 1964). Seedlings treated with concentrations of GA greater than 300 ppm were very spindly and had small leaves, while those treated with BA were short and stocky. Seedlings grown under continuous light were taller than similarly treated seedlings under natural light in almost all cases. The distribution and accumulation of total and component dry weights were very different for GA vs. BA treated seedlings. GAs increased total dry weight at slightly low concentrations, but not at high levels (Figure 3). GA was more effective at low levels 4+7 FIGURE 1. 33 Defoliation treatments used to determine effects of defoliation on budbreak of sugar maple seedlings. Vertical line represents seedling stem and horizontal lines represent leaves remaining after pruning. II_| IF. IT LI 35 .cowE may mo uouuo puwpcmum on» aosgw mmcaa aooauum> .mucoEuomuu oaCOaHomouonm can ocoeuos o» mmcaapwom magma Hmmsm mo oncommmu nuzouw .N mmDOHm 36 15:: 20.2323on 8a. can con om. o __I.I.I.I.I..I.l.l.I.I.l..l.l.IMT.I.l.l.l.l.I..l.l.l.h......I%3«fl.l. __ V \ $.\ \ a (a + .953: ..I.I._ ~.1.¢ .mmcaacwmm mamas woman mo ceaumanfidoum unmao3 who amuou co mucmEummuu teammmouonm 0cm mcoauos mo muoommm .m WMDUHm 38 1:9: 20.29.2323 m 88:. 08. So can on. o o (- ... .955: Tz /’ ' ” I I (a + 32.050193 n + 9.: o: 5.34“” + no.5”!— __ N+Q(0 ¢ _Do¢OEO—uu3a «(O + 3303:0133 O (OOIJ‘CW) IHOIJM no 1V101 N P or 9. 39 under both photoperiods than was GA3, suggesting that GA may be the active GA in sugar maple stem elongation. 7 BA greatly increased dry weight at 150 ppm but strongly decreased it at higher concentrations under both photo- periods. The increase was due to increased root and shoot dry weights (Figure 4). GA4+7 and 6A3 increased only shoot dry weight (Figure 4). Root:shoot ratios for the 2 GA treatments generally decreased with increasing concentration, indicating an alteration of the normal distribution of photosynthate (Figure 5). In contrast, the root:shoot ratio of BA-treated seedlings increased with increasing concentrations due to an inhibition of root growth, rather than to a redistribution of photo- synthate. This inhibitory effect of cytokinins on root growth has been observed for other species (Gaspar and Xhauffaire 1967). Significant interactions between seedlot and gib- berellin concentration were evident, with certain seed- lots being much more responsive to GA than were others. Some seedlings grew very rapidly, then the upper portion of the shoot died. These seedlot interactions could be due to either differences in sensitivity or to differences in the seedlings' ability to absorb and translocate the exogenously applied GAS. No such interactions were observed with BA. FIGURE 4. 40 Dry weight distribution of sugar maple seed- lings treated with various hormones and photo- periods. (A) Gibberellin A4+7 (B) Gibberellin A (C) N-6-Benzyladenine. Photoperiods con- s1st of natural and continuous consisting of natural plus fluorescent light during the natural dark period. Vertical lines equal the standard error of the mean. 41 8 v- I a E .- 2 9 II 3 E O o I l l l f ‘9 - nuzvuoumu C _ _.._ Oct-l: lupplomonnl _______ shod: supple-noun! ‘6 ; I\ .__.._ r009: wpplononnl A ._. ............... too-I: natural 12 ’I "\ _.-.-. alumna-“rd I \\ W root: occur-l 0 150 300 goo FIGURE 4 communion (nun) 42 .comfi map mo uouum Unopcmum may amsgm mmcaa amoauum> .mmcaaoomm magma woman mo Canon uoonmuuoou may no mucmsummuu UOaHOQODOSQ can OGOEHos m90aum> mo myommmm .m mmDOHh 43 DON: .52: 29252320 600 u can on. m mmDUHm O t q 3 q 0”." 100N531008 44 The results indicate that the gibberellines and BA can be of practical value in manipulating growth of seedlings when they are used at the proper concentrations. They can be especially useful for manipulating the root: shoot ratio of seedlings. Seedlot-GA concentration interactions indicate that these hormones must be used with caution, otherwise growth of some seedlots can be adversely affected. Experiment 2. Comparative effectiveness of GA3 vs. GA7. Experiment 1 indicated that GA4+7 increased shoot growth rate and dry weight accumulation more than GA3. The trees treated w1th GA4+7 too spindly for good survival and growth after outplant- and GA3 were generally ing due to frequent spray with high GA concentrations. Experiment 2 was an attempt to accelerate both height and weight growth of seedlings by treating with optimal concentrations and to determine which GA was more effec- tive. All GA treatments greatly increased height, and GA7 was twice as effective as GA3 at each concentration (Figure 6). The effect of GA was due to an increase in both number of nodes and internode length. The dif- ferences between GA types and concentrations were due to increases in internode length. Dry weight did not parallel height in GA treat- ments. Total seedling dry weight generally decreased 45 FIGURE 6. Comparisons between GA7 and GA3 with respect to height increase and dry weight of sugar maple seedlings. Vertical lines equal the standard error of the mean. 46 .9. x as; 5.20;; >80 auomno uoou How mmcaapomm mom» ummuom mcazoum How vamMm vasomoupwn d .a mmeHm FIGURE 1 63 64 chloride (PVC) tubing running the length of the system. This allows for recirculation of nutrient solution for several days. Root trays are made from 2 mm PVC sheets with removable aluminum lids (Figure l). Trays are 10 x 30 x 61 cm. A false bottom was found to increase the versa- tility of the system by allowing for the study of trees that produce small diameter roots and grow slowly in height (e.g., sugar maple) as well as trees that produce large diameter roots and grow rapidly in height (e.g., black walnut). Removal of the false bottom allows place- ment of a germinating walnut in the system, especially since the first leaves appear several centimeters up the stem. However, with sugar maple, stem height growth is relatively slow during the time of expansion of the first leaves, thus requiring the use of a false bottom to raise the leaves above the lid of the root tray (Figure 1). When trees are placed in the plant holder (Figure 1), cotton must be packed around the stem to keep the tree in a suitable position, and the root sys- tem must be covered with plastic, keeping a small (0.5 cm) space between the nylon cloth and the plastic, to main- tain high relative humidity and prevent root dessication and root "humping." 65 Plant Material and Experi- mental Design Sugar maple seed from a single seedlot were air- dried at room temperature to 30% moisture. They were stratified in moist perlite at 3° C for 4 months, then germinated and sown (January 24) in the trays, using 6 trees per treatment. Treatments were natural light, natural light plus gibberellin A (GA7), continuous 7 light, and continuous light plus GA7. Supplemental light 23.1) was provided by fluorescent tubes during (100 chm" the night to provide a continuous photoperiod. GA7 treatments were applied as a foliar spray at biweekly intervals for 8 weeks beginning at 5 weeks of age. GA7 was applied at 200 ppm in a water, ethanol, and 0.1% Tween-80 solution. A quarter strength general purpose nutrient solution, pH 5.5-6.0, was supplied. Root and shoot growth and development were monitored by weekly photographs from which measurements of growth were made. The data were analyzed using analysis of variance, and differences among treatment means were evaluated with Duncan's Multiple Range Test. Results and Discussion Performance of the Hydro- ponic System Root systems in the hydroponic system were better developed than those of equal age greenhouse-grown and one-year-old nursery-grown seedlings (Figure 2), although FIGURE 2. 66 Comparison of root development of sugar maple seedlings grown 3 months in paper plant containers containing an artificial soil mix, 3 months in an irrigation-type hydroponic system, and 1 year in an out- door nursery. FIGURE 2 68 root development in greenhouse-grown and hydroponic-grown seedlings were about a third taller than those in root trays. Of particular interest was the observation that one-year-old nursery-grown seedlings had relatively poorly developed root systems with respect to both root length and number. Obviously, the 3 different environ- ments have influenced the intensity and course of root growth. This observation is common when comparing root development between heterogenous root and shoot environ- ments (Lyr and Hoffmann 1969). Stem height growth followed the pattern often observed for sugar maple seedlings in greenhouse and nursery environments (Figure 3), being most rapid during the first week after germination and ceasing by the fourth week, with formation of a resting bud that will usually not reflush without cold treatment. Root and shoot growth rates were parallel during the first 3 weeks following germination, although root growth was about 50% greater than shoot growth during the first week. This suggests the adaptive importance to a young seedling of establishing a root system capable of supplying support, nutrient elements, and water very soon after germination. Growth in height ceased after 3 to 4 weeks, and primary root (tap root) growth dropped to half the first week's rate. During this time secondary roots were developing, but their growth rate was also decreasing. This general FIGURE 3. 69 Root and shoot growth rates of sugar maple seedlings grown under a natural photOperiod in a hydroponic system. Week 0 = January 24. Vertical lines equal the standard error of the mean. Primary root equals tap root. Secondary roots refers to the 6 longest secondary roots. 7O secondary roots \ \ \ III 4 - u 2 \xxx 2 \x 2 ll \\\ m m 1T m r .I o. + Ill ... 8 w. w. ...I .. ... a 0 III]! .....r. 6 Aov m m .vall .....T 1...»: h c" 2" \\\ s\ ... k S D. D. ((((((( x .....T .4: G _ . I n... ((((( II...|I. .. e . [Iii l..| 2 W — . \\ ....o 1" . u ‘‘‘‘‘ . i _ .1 \\\\\\ .Iurll 0E . _ ... ...... ..... .. G \\\\\\ 1...... 8A (...... II.........|. ..................... ......l1I 6 ...... ......I... Illlqull I”! \ 4 hhv/I h...\\| \\AHHWTMH. at £331fllri¢a , 0 8 6 4 2 O 8 6 4 2 0 1. 1. 1. 1. 1. 33?: 2.3. 1:596 FIGURE 3 71 decline in stem height and root growth rates possibly reflects the transfer of photosynthate to expanding leaves and the thickening stem. The primary root and total root system (primary root plus major secondaries) resumed rapid growth after the third week and continued without declining for 4 additional weeks. During this time, growth rate of the root system was not only much greater than that of the primary root but was accelerat- ing, suggesting that development of the major secondary roots has priority over primary root growth during this stage of seedling development. After about 8 weeks of age, growth rates of both the primary and the major secondaries declined steadily with intermittent spurts of increased growth (Figure 3). The greater decline in growth rate of major secondaries relative to that of the primary root suggests that primary root growth is more important at this stage of development. After 6 months, mean primary root growth had stabilized at about 1 cm per week. However, primary root growth in some trees had completely ceased by this time, even though leaves were green and apparently photo- synthetically active. Perhaps the basal metabolism of the seedling required most of the photosynthate, leaving very little for new growth, or photosynthate was going into root storage products rather than growth. If the latter were true, then longitudinal root growth may not 72 be as important as radial growth at a certain point in development. Roots of trees in temperate latitudes experience a period of rest in winter. The beginning of this period depends upon the species and upon the environment (Lyr and Hoffmann 1969). Rest may be responsible for cessation of root growth, even though the foliage is still apparently actively photosynthe- sizing. A second flush of root growth occurred 4 months after germination (Figure 3), corresponding with the natural second flush that most trees experience in autumn (Lyr and Hoffmann 1969). This so-called "autumn" peak occurred in major secondary roots but not in the primary root, suggesting that development of the entire root system is more important than development of only the primary root during this second period of activity. Shoot and root growth rates resulting from the hydroponic technique paralleled very closely the reported growth pattern exhibited by trees growing under natural environments. This means that the technique probably provides an environment suitable for root growth which is close to that of the outdoor environment, thus allow- ing experimental manipulation. The hydroponic system is, therefore, useful for studying many aspects of root phy- siology and genetics since it allows continuous and simultaneous observation or measurement of root growth and development. 73 Root growth rates indicated correlative recip- rocal effects between roots. Certain major secondary roots grew at rates highly correlated with primary root rates, while others did not. Perhaps this reflects a balance in roots just as there is an Optimal balance in root/shoot ratios (Kramer and Kozlowski 1960). This is supported by the observation that on several occasions either primary root or major secondary roots would cease growth for several weeks and then resume growth. This renewed growth was often rapid, commonly doubling its length within 2 or 3 weeks. Secondary roots forming near the base of the primary root during the first 2 or 3 weeks after germi- nation generally did not develop into major secondary roots. They grew very rapidly for 2 or 3 weeks then‘ either ceased growth or died. Secondary roots were initiated about 1 week after primary root emergence, while tertiary roots about 2 weeks later (Figure 4). Tertiaries did not exceed secondaries until after 20 weeks. After 6 months the major roots had almost ceased growth; however, a very large increase in the number of minor secondaries occurred at this time, resulting with 70% more secondaries than tertiaries. At 6 months of age, seedlings had an average of 341 roots. There was a large amount of variation in root morphology between seedlings. The root system ranged FIGURE 4 . 74 Cumulative root number and ratio of tertiary to secondary roots in sugar maple seedlings grown under a natural photoperiod in a hydro- ponic system. Week 0 = January 24. Vertical lines equal the standard error of the mean. 20 0 FIGURE 75 IIIIIIIIIIII 'er'iary -....- secondary _. _____ tertiary / secondar I I I-----‘) I’ \ I \ I \ .’ \\ o. A ’ ’ \ I \ I \ . I” \\ x’”, \\ .l I L “.1 I, h -\ / ! x ,’ .l \\ \ x .I ”H I J “I ‘ I . 00““ I .9} '1 ll fifie‘v+ F.’. I e .+{"‘ ‘ I I J I, {:‘L“ ‘é‘. o 2 4 6 8 101214161820222426 AGE (weeks) 4 d C d “bibbuabs LA TERTIARY/ SECONDARY 76 from trees with a very strong primary root with few major secondaries to trees with essentially no primary root and many secondaries. Thus, there is either a large amount of genetic variation in root morphology and/or root morphology is easily affected by small changes in root environment. If these differences are primarily genetic, then much potential should exist for selecting and breeding and tailoring root systems for the environ- ment in which trees are to be grown. This possible wide variation in root form suggests the potential for using intergenotypic interactions to increase unit area yields of forest products. Allard and Adams (1969) have suc- cessfully used this technique to increase the yield of similar grain varieties by 6%. Use of more diverse varieties could result in yield increases of 25%. In light of the possible genetic variation observed in sugar maple, genetics of competition with respect to intraspecific root differences warrants investigation. Upon defoliation of a single seedling at about 16 weeks, an immediate cessation of root growth was observed. This supports the observation of Webb (1976) who found that root elongation rates of first—year sugar maple seedlings appeared to be dependent on current photo- synthate production by the shoot. 77 Effects of Photoperiod and GA7 Photoperiod did not affect cumulative growth of the primary root and major secondaries; however, GA7 treatment inhibited root growth (Table 1) within 3 weeks of initial treatment (Figure 5), primarily by reducing growth rates of major secondary roots. There was no effect on primary root elongation rates (Table l). GA7 also greatly decreased the number of secondary and ter- tiary roots, while photoperiod had no effect. There were no photoperiod-GA interaction effects on any measured 7 variable. Supplemental light and GA7 treatments induced various degrees of budbreak (Table l), and the effects were additive. The resulting increases in shoot growth reduced root-Shoot ratios significantly. 78 .umoa cocoa mamauaaz m.amocoa means wuaaanmnoum mo ao>oa mm 0:» pm ucouommac zaucmoamaCOam uoc who umuuoa mean on» an owsoaaom who noan3 mucwsumouu hm :aaamumnnam no GOaMOQOuonm canvas can Gazaoo m casuaz monam> m muoou aumpcooom umomcoa 0 van noon moem .muoou >Hmccooom “momGOa m can uoou mmea m m.o b a.» om m a.a m me m we m mm m ~.em m ~.~ m moa Ema com a o.a m a.a m m a.a a mm 9 mm A wma n o.vm m m.m n «ma sum 0 ha :aaaonmnnaw m S.o a o.n me m ~.a m mm m we m moa m S.me m ~.~ m Sea amucmemaaasm n a.a m m.h ma m o.a m am a vm m moa m o.mv m m.m mm oma amunumz vOaHomouonm EU a nonssz Honssz Honfiaz x3\Eo x3\Eo Eu caumm oaumm SwamSm boom uoonm unwaom xmoum myopcooom whoauuos >uo©cooom amuoa uoom moa £u3ouw m ucoEumoua 0» poonm cam 0» aamuoe uoom >MMauuo9 OQSB uoom ovum suzouw magma Hmmsm mo nu3oum uoonm .Eoumxm vasomoupwa om>pIGOauomauua co Ca czoum mmcaavoom paw uoou :0 mucofiumouu hm :aaaouonnam can poauomouosm mo muoommm .a mam¢9 FIGURE 5. 79 Cumulative root growth (tap root and 6 longest secondary roots) of sugar maple seedlings grown under 2 photoperiods (natural vs. continuous with supplemental fluorescent light during the normal dark period) and 2 gibberellin A7 (0 ppm vs. 200 ppm as a foliar spray at biweekly intervals) treatments. Week 0 = January 24. Vertical lines equal the standard error of the mean. 26 A 24 E 22 3’ 20 I 18 316 “14 601' IV I—1O CUMULA 0'0me FIGURE 5 80 ............ supplemental ...... natural - .. - supplemental + GA 7 - ..... natural + GA 7 ‘1 0 2 4 6 8101214161820222426 AGE (weeks) CHAPTER IV LACK OF EFFECT OF TRIACONTANOL ON GROWTH OF SUGAR MAPLE SEEDLINGS Abstract Triacontanol, a 30-carbon primary alcohol, with growth-promoting effects in some plant systems, was evaluated to determine if it has potential for acceler- ating and/or altering sugar maple (Acer saccharum Marsh.) seedling growth. Foliar spray applications of 0, l, and 10 ppm triacontanol applied as both single and repeated weekly treatments did not significantly promote or inhibit height growth, total leaf area, root to ShOOt ratio, total dry weight, component dry weights, or bud dormancy. Introduction Triacontanol is a naturally occurring straight- chain 30-carbon saturated alcohol (CH3(CH2)28CH20H) which promotes growth and markedly increases harvest yields in several horticultural and agronomic crop species (Ries and Wert 1977; Ries et al. 1977; Ries et a1. 1978; Han- garter et al. 1978; Bittenbender et a1. 1978). Most of 81 82 the tested species have been either annuals or biennials. Their response warrants an evaluation of triacontanol's effectiveness on perennial woody species such as fruit and forest trees. Our objective was to determine if triacontanol would promote growth of sugar maple (Aggr saccharum Marsh.) seedlings. Materials and Methods Sugar maple seed for this study was collected from several Michigan sources and bulked. Seeds were air-dried at room temperature to about 30% moisture and stratified 4 months at 3° C in moist perlite. Germinated seedlings were sown in 5 X 5 X 28 cm polycoated paper plant bands filled with a peat-vermiculite-perlite (1:1:1) potting mix and contained in plastic cases. Seedlings were grown in a greenhouse under natural day- light supplemented with 100 chm-zs”l of continuous fluorescent light during the night. Greenhouse temper- atures ranged from 20° to 30° C. Seedlings were grown at near optimum moisture and nutrient levels. They were fertilized with 25-0-25 Peters solution every two to three weeks. Seedlings were planted in a randomized complete block design with 4 replicates. Triacontanol was applied in 3 concentrations and 2 modes of application. Plot means were composed of 12 trees. Triacontanol was applied at 0, l, or 10 ppm in a water emulsion with 0.1% 83 Tween-20, either as a single foliar spray to runoff or 10 consecutive weekly sprays. Treatment began 3 weeks after germination when leaves of the first node were about 75% expanded. Sprays were applied in early morning when the greenhouse temperature was generally near 20° C. Solutions were refrigerated between sprayings and allowed to warm to room temperature before application. The seedlings were measured in October after 4 months of growth, and the data analyzed by analysis of variance, using Duncan's Multiple Range Test to test the signifi— cance of treatment differences. Results and Discussion Triacontanol had no promotive or inhibitory effect of height growth, total leaf area, root to shoot ratio, total dry weight, or component dry weights. Visual observation did not suggest any differences in leaf mor- phology (Table 1). Thus, triacontanol does not act as a growth regu- lator in sugar maple seedlings, at least under the experi- mental conditions imposed here. Possibly the concentration of triacontanol was not high enough to induce a growth response, although the same concentrations are effective in promoting growth in several horticultural and agronomic species (Ries et al. 1978; Ries et a1. 1977). The rela- tively high daytime temperature at which the seedlings were grown resulted in poorer seedling growth than that 84 .wuaaanmnoum mo aw>oa wm on» up ucmoawacmam mwocmummmap oz a was mam mmv.a amm.e am~.a mos. Sam.~ Ema ca ama mm~ mma.a moe.e SSI.I mmm. mme.~ sad a «II sum Sam.a Sam.q oka.a mam. ~m¢.~ Sam o mwmumm pmumomom SNH new mea.a mm~.e mm~.a we». sm~.~ sag ca maa «mm m-.a Gem.¢ me~.a Ran. oov.~ sad a sea mom «Ho.a meo.v mo~.a mam. mom.~ Ema o wwumm mamcam 85 ~50 m m m m aouoa mm>mma Ewum Doom unwao: comm mama uommwwmoom cowumwawmmm . imam: sun m p n z mo mCOauooaammm umaaow ou macaacmom mamas ummsm mo noncommmu nu3ouo a.aocmucoomauu .a mamde 85 observed at cooler temperatures. This may have prevented action of triacontanol, assuming it is active in sugar maple. If true, there may be a triacontanol-temperature interaction. Triacontanol may exist in the xylem sap of sugar maple trees (Robert Haus, personal communication). It increased to a very low concentration just prior to spring budbreak and later decreased. This observation suggests that triacontanol may play a role in regulating budbreak. However, the seedlings in our study were treated before, during, and after budset, and there was no apparent effect of triacontanol on date of budset or on budbreak. This suggests that either triacontanol is not involved in budbreak or it acts in conjunction with another growth promoters or inhibitors. This study indicates that under the described set of experimental conditions triacontanol does not stimulate growth of sugar maple seedlings, and therefore has no potential for accelerating and/or altering tree seedling growth such as described by Hanover (1976). However, it may be effective on other tree species either as a spray or as a seed oak (Ries et a1. 1978). CHAPTER V CARBON DIOXIDE, TEMPERATURE, AND AGE EFFECTS ON GROWTH, PHOTOSYNTHESIS, AND DARK RESPIRATION OF SUGAR MAPLE SEEDLINGS Abstract Sugar maple (Acer saccharum Marsh.) seedlings grown 4 months at elevated atmospheric carbon dioxide levels (700, 1400, and 2100 ppm) elevated levels resulted in substantial increases in height, organ dry weights, and leaf area with increasing carbon dioxide concentra- tions. The photosynthetic mechanism of these seedlings was adapted to the environment in which they develOped, but respiration was not. When seedlings preconditioned at either 1400 or 2100 ppm carbon dioxide were grown in a 700 ppm environment for 2 weeks, net photosynthesis decreased by 25%. Seedlings grown continuously at 20° C were 94% taller and had 2.5 times more nodes than those at 30° C. The photosynthetic system apparently adapted to the tem- perature at which the seedlings developed. Photosynthe- tic measurements of seedlings preconditioned at 20° and 30° C and subsequently exposed to 30° and 20° C, 86 87 respectively, showed an 18% decrease in net photosyn- thesis. The photosynthetic mechanism was capable of readapting at least twice to new temperature environments. Rates of photosynthesis and dark respiration in greenhouse-grown seedlings generally were highest early in development and decreased with leaf age, regardless of leaf types. A large increase in net photosynthesis always followed budset. At 22 weeks after germination, sharp decreases in both photosynthesis and dark respir- ation occurred in all seedlings, regardless of leaf type. At 32 weeks, rate of respiration exceeded that of net photosynthesis. Introduction Accelerating and manipulating growth by controlling environmental factors is advantageous in the production of forest tree seedlings for both research and commercial purposes (Hanover 1976, 1977; Logan and Pollard 1976). Atmospheric carbon dioxide level and temperature are 2 factors that greatly influence seedling growth and develop- ment and may affect growth even after outplanting due to acclimation or adaptation to the greenhouse environment. Exposure of seedlings to higher or lower temperatures may result in a decrease in photosynthetic rates and change the point of Optimal photosynthetic temperature. Many woody species experience temperature-related adaptive 88 changes in both photosynthesis and respiration (Mooney and West 1964; Rook 1969; Strain 1969; Strain et al. 1976; Strain and Chase 1966). Photosynthesis of forest tree seedlings in out- door or greenhouse atmospheres is almost always below Optimal levels because of low CO2 concentrations (Salis- bury and Ross 1969). CO -enriched atmospheres are used 2 in greenhouse production of horticultural and field crops (Wittwer and Robb 1964; Ford and Thorne 1967). Growth of many tree species is stimulated by C02 enrichment (Funsch et a1. 1970; Yeatmen 1970; Zimmerman et al. 1970; Stanley 1971; Tinus 1976; Wood and Hanover 1979). This technique might accelerate tree seedling growth and development for physiological and genetic evaluation but has received very little attention. It may be possible that CO2 levels can also induce adaptive responses in forest trees. Sugar maple seedlings typically exhibit a deter- minate growth habit and grow relatively slowly under con- ditions that greatly accelerate growth of seedlings of many other forest tree species. An understanding of the developmental patterns of photosynthesis and respir- ation in leaves might aid in overcoming this problem. Knowing how long the leaves can be expected to produce significant levels of photosynthate is also important. 89 The objectives of this study with greenhouse- grown sugar maple seedlings were to determine: (a) the influence of CO2 and temperature on growth, net photosyn- thesis, and dark respiration; (b) adaptation of the photosynthetic and respiratory mechanisms to certain CO2 and temperature levels; and (c) age differences in photosynthesis and dark respiration of leaves from seed- lings in different developmental states but of equal age. Materials and Methods Seeds were collected from natural forest in Michigan and kept separate by seedlot. They were air- dried at room temperature to about 30% moisture and stratified 4 months at 3° C in moist perlite. Germinated seedlings were then bulked and planted in 5 X 5 X 28 cm polycoated paper plant bands containing a topsoil-peat- perlite (1:1:1 v/v) potting mix. Experiment 1. The purpose Of this experiment was to investigate the potential for accelerating seedling growth by C02 enrichment of the atmosphere and to deter- mine if the photosynthetic and dark respiratory mechanisms become adapted to these elevated CO2 levels. Seedlings were grown in air-tight transparent fiberglass chambers within a greenhouse and were exposed to normal light 2 during the day and to 100 chm- s"1 of continuous supple- mental fluorescent light during the night. Continuous 90 light was used to prevent budset due to imposition of long nights from becoming a limiting factor in height growth. Temperature within the chambers ranged from 20° C at night to 35° C during the day. Experimental design consisted of 3 blocks, each with 3 CO2 concen- trations--700, 1400, and 2100 ppm, and 36 trees per treatment. These levels were monitored daily with a Beckman 864 infared gas analyzer and maintained at i 100 ppm by bleeding in CO2 gas. Chambers were opened to the greenhouse atmOSphere for a few minutes every 3 or 4 days to allow fresh air to replace air within the chambers. Fans in each chamber provided continuous air movement. After growing 4 months in COz-enriched atmospheres, growth measurements were made and healthy appearing seed- lings were transported into the laboratory for photosyn- thesis and dark respiration measurements. After removal from the CO2 environment in which they were grown, seed- lings were exposed to greenhouse ambient CO2 levels (approx. 700 ppm) for 2 weeks, then preconditioned in each of the 3 test environments for 1 hour, then tested at each CO2 level used in the growth phase. Initial CO2 level was established by exhaling small amounts of C02- enriched air in the vicinity of the uptake tubing from the pump to the chamber. The attached leaves of 3 seed— lings (3 trees per plot mean and 3 replicates) were 91 sealed in a water-jacketed plexiglas chamber (0.95 1). Illumination was provided by one 400-watt color-improved mercury vapor lamp positioned above and perpendicular to the leaf surface. Photon flux density at the leaf surface was 500 chm-zs_l (3,200 ft. c.), as determined by a Lambda quantum sensor. Temperature was maintained at 25° 1 0.5° C by circulating water from a constant temperature bath through the plexiglas water jackets. Air flow was at 400 cc min. ‘1. Net photosynthesis and dark respiration were determined by measuring the rate of CO change (mg/dmZ/m) in a closed system between 670- 2 730 ppm, 1370-1430 ppm, and 2070-2130 ppm. Dark respir- ation was measured after each photosynthetic measurement by placing a black cloth over the leaf chamber. Leaf area was then measured with a Lambda LI-300 portable area meter. Experiment 2. In this experiment, we wanted to investigate the sensitivity of sugar maple seedling growth to temperature and to determine if the photosyn- thetic and respiratory mechanisms of sugar maple can become adapted to the temperature conditions in which they are grown. Three blocks of seedlots (from 12 bulked sources) were germinated and grown for 2 months in the greenhouse under continuous light. They were then trans- ferred to growth chambers at constant 20° or 30° C. 92 Height and node number were recorded after 2 months under these conditions. Photon flux density was 100 11Ecm-zs-1 from an arrangement of fluorescent and incandescent light bulbs. The vapor pressure deficit in both chambers was 12.5 mmHg. To determine whether or not temperature adaptation occurs in sugar maple, seedlings were moved to growth chambers after 3 months in a greenhouse under continuous light. They were placed in a split-plot design with 6 blocks of 2 growth temperatures and 2 measurement temper- atures. Growth and measurement temperatures were 20° i 0.5° and 30° 1 0.5° C. Means for CO2 exchange rates were composed of 3 trees. At the end of 3 months photosyn- thesis and respiration were measured at each of the test temperatures and the seedlings were then transferred to another chamber and grown for 1 month at 25° C (a neutral temperature). Photosynthesis and respiration were then measured at each of the test temperatures. Photosynthetic and respiratory measurements were the same as in the previous experiment with respect to instrumentation and light conditions. Attached leaves of 3 trees were placed in the leaf chamber at the test temperatures and allowed to precondition for about 1 hour. CO2 exchange rates were measured at both 20° and 30° C for trees grown at these 2 temperatures, with sequence random. Only seedlings with 2 leaves (1 node) were used. 93 Experiment 3. To determine develOpmental dif- ferences in photosynthesis and dark respiration of green- house-grown trees, bulked seedlings (from 20 Michigan sources) were grown 32 weeks (from germination) in a greenhouse where temperatures ranging from 20° to 40° C. Supplemental fluorescent light at 100 IJEcmt'zs—l during the night provided continuous photoperiod. Trees were planted in 4 blocks with 3 tree classes (single node, double node, and triple node: totaling 6 leaf types), and measurements were made 20 times over a period of 32 weeks. The plot mean for the CO2 exchange measurements consisted of 3 trees and this was replicated 3 times. Sugar maple seedlings grown in the greenhouse typically produce 1 leaf node and then promptly set bud; a few weeks later they may break bud and produce 1 or more new nodes before setting a resting bud. Therefore, trees are pro— duced having 1, 2, 3 nodes, etc. Instrumentation and light and temperature treat- ments for the CO2 exchange measurements were the same as in Experiment 1. Seedlings were watered to field capacity 2 days prior to measurement. They were preconditioned to the test conditions for 15 minutes. Leaves were then cut from the shoot and the petiole immersed in a small test tube containing distilled water. Measurements were com- pleted within 20 minutes. CO2 exchange rates were measured between 300 and 360 ppm. Preliminary studies 94 showed that CO2 exchange rates were not affected until 45 minutes after detachment. Results and Discussion Experiment 1. Height, leaf area, and organ dry weights Of sugar maple seedlings were greater in enriched CO2 atmospheres (Table 1). These responses increased with increasing CO2 levels, although growth increase per unit CO2 added declined. Seedlings at the 2100 ppm level had 62% more dry weight and a reduced root:shoot ratio relative to the controls (700 ppm). This ratio difference was primarily due to an increase in stem weight. Diminishing returns for dry weight gain increase per unit increase of CO2 may be attributed to (a) C02 saturation of the photosynthetic reactions and (b) the known interaction between light intensity and CO2 may occur (Salisbury and Ross 1969). C02 is generally the limiting factor in photosynthesis; however, at high CO2 levels light intensity becomes limiting. This is illus- trated in Figure l by the ObServation of diminishing returns of net photosynthesis with increasing CO2 levels at a constant photon flux density. A plant can more efficiently use CO2 at high atmospheric levels when light intensity is high. When intensity is low, efficiency of CO2 utilization is greatly diminished (Salisbury and Ross 1969). This means that a grower can use CO2 more 95 .ume mmcmm mamauanz m.cmucso ha am>ma mm may no unmnmmmap aaucmoamacmam mum HODDOa mean can >3 Om3OaaOm no: can cEano m casua3 mosam> a m ap.a a eaa o mom a owoa o omoa a me o moa Sam ooam n m~.~ m ooa n can a cam b omea n km n ma Sam ooea n wo.~ a mm m mew m och m owed a am am am Ema och IIIIIIIIIIIIIII OEIIIIIIIIIIIIIII ANEOV AEEV mm>mma Eoum uoom aouoa pond mama Hobos ucwficoua>cm £u3ouw mpaann conumo poonm\uoom unmamm unmao3 aha .mmcaapwmm magma noosm mo cu3oum :0 maw>ma wpaanO conumo mo muommmm .a mamda 96 FIGURE 1. The effects of carbon dioxide concentration on net photosynthesis and dark respiration of sugar maple seedlings preconditioned in 700, 1400, and 2100 ppm carbon dioxide atmospheres. Vertical lines equal the standard error of the mean . 97 3.6 3.2 .'° on 1° a. 2.0 'I/. 0 ,__0' 700 not photosynthesis Q” 0....-.0 1400 n61 photosynthesls O .......... O 2100 net photosynthesis 700 dark resplratlon 1.2 ..... 1400 dark resplratlon ................ 2100 dark resplratlon €02 EXCHANGE RATE (mg €02 dm‘z M4) at 700 1400 2100 co2 MEASUREMENT LEVEL (Ppm) FIGURE l 98 effectively by tailoring the CO level to the light 2 intensity in the greenhouse. CO2 levels should be rela- tively high during the day but should be allowed to decrease to the ambient level during the night. Our observations indicate that growth of sugar maple seedlings can be increased by the incorporation of CO2 into the cultural system. As a result of such a practice trees should be more vigorous for outplanting and other uses. The photosynthetic mechanism was affected by the environment in which seedlings were grown (Figure 1). Trees grown in 700 ppm CO2 produced more net photosynthate when measured at the 700 or 2100 ppm level than did seed- lings grown at higher CO2 levels. Trees grown at 2100 ppm produced the least net photosynthate when measured at the 700 or 1400 ppm level but were intermediate in production at the 2100 level. These observations indicate that the photosynthetic mechanism of seedlings is affected by the CO2 environment in which they are grown. Enzyme or iso- enzyme changes in the reductive pentose phosphate pathway may occur. CO2 adaptation in Chlorella has been attributed to changes in the activity Of at least one of these enzymes (Reed and Graham 1977). Dark respiration was not affected by theCO2 level in which seedlings were grown (Figure 1). Increasing CO2 levels decreased dark respiration for all 3 treatments. 99 Dark respiration rates at 1400 and 2100 ppm were only 75 and 38%, respectively, Of that at 700 ppm C02. This study illustrates the potential usefulness of CO2 fertilization of greenhouse-grown trees. The photosynthetic mechanism Of seedlings can be expected to be adapted to the CO2 concentration in which they develop. Seedlings grown at a relatively constant high CO2 level may experience a reduction in net photosynthesis of 25% or more for at least 2 weeks after outplanting. Whether the photosynthetic mechanism will readapt to the ambient outdoor CO2 environment is unknown; however, it seems likely. If leaves are unable to readapt to the out- door level, then chances Of survival after outplanting may be affected; but if readaptation is possible, it should be done before outplanting. This could be accom- plished in either of two ways: First, they could be moved to the outdoor environment and allowed to readapt before outplanting; second, a period of growth at a lower CO2 level could be imposed on the seedling prior to removal from the greenhouse. This might produce seedlings that are adapted to both high and low CO2 levels. Experiment 2. After 2 months at constant temper- ature sugar maple seedlings were 94% taller and had 28 times as many nodes at 20° than at 30° C (Table 2), and growth was active only at 20° C. A cool environment 100 TABLE 2. Effects of temperature on growth of sugar maple seedlings. Growth Temperature Height (cm) Nodes o l 30 C 6.8 a 2 a 20° C 13.2 b 5 b 1Values within a column and not followed by the same letter are significantly different at the 5% level. 101 appears to be essential for growing large sugar maple seedlings in greenhouses. fixUnder natural conditions, height growth Of sugar ... / maple seedlings occurs in early spring when temperatures are relatively low. By late spring or early summer, when temperatures are relatively high, seedlings have set a resting bud which generally does not break until exposed to about 2000 hours of temperatures 5° C or lower (Taylor ‘x. and Dumbroff 1975). This determinate growth may be largely controlled by relatively high temperatures experienced in late spring or summer. Previous obser- vation of greenhouse photoperiod studies with sugar maple showed that exposure to continuous light and warm (23° to 35° C) temperatures increased height growth and node formation slightly in comparison with natural photoperiod controls. This effect could be either photoperiodic or ,photosynthetic. Certain forest tree species have been shown to be photoperiodically sensitive with respect to Charmancy (Young and Hanover 1977; Butler and Downs 1960; Nitsch 1957; Williams et a1. 1972). If sugar maple is Ffliotoperiodic sensitive, then these observations suggest triat phytochrome may be a switching system for regulating hfaight growth and bud formation, while temperature con- tltols expression Of the phytochrome response. Temperature Ccruld conceivably affect the relative levels of growth 102 promoters and inhibitors, with promoter levels being higher and inhibitor levels lower under long days and cool temperatures (20° C). After seedlings had grown 3 months at either 20° or 30° C, net photosynthesis and dark respiration were well conditioned to these temperatures. Net photosyn— thesis of seedlings grown in both environments decreased when measured at the other growth temperature (Figure 2). Dark respiration of trees grown at 20° C increased two- fold at 30° C; however, temperature did not affect dark respiration of trees grown at 30° C (Figure 3). These differences were probably not due to inadequate precon- ditioning, because there was no difference between measurements made at preconditioning periods of 30 minutes or 24 hours. Growing temperature did not significantly effect net photosynthesis when measured at the temperature at ‘which the seedlings were grown, i.e., net photosynthesis (of trees grown at 20° and measured at 20° C did not ciiffer from trees grown at 30° and measured at 30° C (Figure 2). This was also true when measured at the 1:emperature in which they were not grown, although net I>hotosynthesis decreased 18% in both treatments. This :indicates that changes occurred in both cool and warm Eadapted seedlings that allowed them to maximize photo- Synthetic rates under each temperature environment. TPhis adaptation of CO2 exchange to temperature has also 103 FIGURE 2. Effects of cool and warm temperatures on net photosynthesis Of sugar maple seedlings grown in constant cool or warm environments. Vertical lines equal the standard error Of the mean. 104 1.2 U 30": 3mo. 1.0 20' :3 mo. NET rnorosvmussls (me C02 clwr2 hr") ‘ 20° :3 me. + 1mo. at 25° 30° : 3 me. + 1mo.at 25° 20 30 GROWTH TEMPERATURE (C°) FIGURE 2 105 FIGURE 3. Effects of cool and warm temperatures on dark respiration of sugar maple seedlings grown in constant cool or warm environments. Vertical lines equal the standard error of the mean. 106 1.2 1.0 3 3mo. +1 me. at 25° «'- 3mo. : 3mo. + 1 mo. at 25° DARK RESPIRATION (ms co, dun-2 M4) 20 30 GROWTH TEMPERATURE (C°) FIGURE 3 107 been observed in a number of other species (Mooney and West 1964; Rook 1964; Strain 1969; Strain and Chase 1966; Strain et a1. 1976). The ability to adapt to temperature probably provides a distinct selective advantage which increases survival under a wide range of temperature con— ditions. This characteristic may be a major factor con- tributing to the ability of sugar maple to occupy such a wide natural range (Fowells 1965). Seedlings of both treatments were grown in a common greenhouse environment with temperatures ranging from 20° to 35° C for 2 months then transferred to growth chambers and exposed to either constant cool or warm con- ditions for 3 months. Thus, any differences were induced within this 3-month period. To better understand the ability of these seedlings to readapt to temperature, they were grown at a constant neutral (25° C) temperature for 1 month after the initial measurement. NO difference in net photosynthesis Of the cool adapted trees was evi- dent at either 20° or 30° C. Net photosynthesis of warm adapted trees was much greater (equal to 20° C trees measured at 20° C) at 20° than at 30° C (Figure 2). Per- haps this latter response is due to accelerated senescence resulting from 3 months of growth at 30° C. This may also account for the lack of difference in net photosynthesis of seedlings grown at 30° for 3 months and measured at 20° C with the same seedlings when measured at 20° after 108 growing at 25° C for 1 month. Dark respiration patterns differed little from the 3-month measurements (Figure 3), escept for an increase in trees transferred from 20° to 25° C. These observations suggest that the dark respir- ation mechanism Of leaves is not as easily adapted as is the photosynthetic mechanism, which adapts fairly rapidly and readapts to the original temperature. Readaptation occurred after leaves were 6 months Old and senescing, hence temperature adaptations are not restricted to young foliage. C>This study shows that growth of sugar maple seed- lings can be greatly accelerated by growing at cool, rather than warm, temperatures. Photosynthetic and respiratory mechanisms of seedlings grown in a greenhouse at a relatively constant temperature adjust to that temperature. When outplanted at a temperature differing from that to which they are adapted, net photosynthesis decreases and respiration may increase. Readaptation to normal outdoor temperature can be expected within a :month or two. Therefore, a delayed temperature adaptation ndght cause a loss in growth for the first few weeks after outplanting. This may be a factor contributing to the difficulty of establishing sugar maple plantings (von Althen 1971, 1972, 1974). 109 Experiment 3. Photosynthetic and respiratory rates for all seedlings were highest in very young expanding leaves (Figures 4, 5, and 6). These rates declined rapidly until budset (4 weeks old). Net photosynthesis increased dramatically 5 weeks after germination, while dark respiration continued to decrease. This response was correlated with budbreak. It was Observed in both seedlings that were about to form new nodes and in seed- lings which did not experience a second budbreak. In leaves on seedlings with 2 or 3 nodes, this increase in photosynthesis was soon followed by a sharp rise in dark respiration rate. Presumably this was a response to the actively expanding newly formed leaves because it did not occur in single node seedlings. Both photosynthetic and respiratory rates then decreased in all seedlings until budset at 10 weeks Of age. During the 2-week period following budset, there was a second large increase in net photosynthesis in almost all leaf types, even though the l—node seedlings did not reflush after the initial budset. However, this increase did not occur in leaves at the lower node of 3-node seedlings. The peak in net photosynthesis just after budset, even in l-node seedlings, suggests a nonrandom relation- ship. The leaves were fully expanded at this time, con- sequently maximum export would be expected to be occurring at this time (Thrower 1964). Something may be preparing 110 . 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State-lac a .250. cote.“ gazes?! ....ov III 0.0 3250. .23.: 3305:3221. .EI _ r .03... 630. » 2.2.2.322... .0: II a 0.6 114 .cmmE m2» m0 Houum oumccmum may Hmsvw mmcfla Hmowunm> .mmooc m Ho N nuHB mmmuu How ammusn @coowm mo mafia Amy .mmco: M MD N Sufi? mmwuu :0 xmwnncan mo mafia an. .osn umm mm: cam Umvcmmxm zaasm mm>mma AUV .Umocmmxm m\~ mm>mma Amy .cmccmmxw m\a mm>mma Adv "msoHHOM mm mum vamEQon>m© mo mmumum was .mmwoc mmma m sufl3 mmzwacmmm magma Hmmsm :3oumlmmsoscmmum mo unmEmon>m© nuflz :ofipmuflmmmu xumc can mfimwzucwwouosm um: :fl mmmcmnu .m mmDOHm 115 ZO_.—11 sugar maple, the results can probably be applied to ITUDSt tree species in general and especially for determi- n ate hardwoods . BIBLIOGRAPHY BIBLIOGRAPHY Allard, R. W., and W. Adams. 1969. The role of inter- genotypic interaction in plant breeding. Proc. 12th Int. Cong. Genetics. 3:349. Bachelard, E. P. 1968. Effects of seed treatments with gibberellic acid on subsequent growth of some eucalypt seedlings. New. 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