f ' MGRPHOLOGEGAL ANATOMELANDg gr PHYSMOGICALRESPONSESOF ; ' ' ~ FDA PRATENSIS L. "MERION' AND ~ ‘ ' I ~ FESTUCA RUBRA L. ‘PEN'NLAW‘N’ T0 * -‘ 3‘ ; REDUCED LIGHT mTEnsmEs ‘ ‘ tionforthe DegreeofthE f g? : EICHEGAN STATE UNIVERSITY ' ‘ ~ ‘ L :2 _ , .WAES FREEMAN wmm ‘ 5.3,. 1973» ’. ‘ ‘ . " " , “I .3.» - r3311?“ "[87]”?! gm“, 1. "r .t-l! ~,lr0"":' :' a~ ‘v.n- l' r! r! 7 «ram 93* fl '7‘, ‘17 ,. I . h ,- ,s-a ; ~99 v‘ F . . water-=3 This is to certify that the thesis entitled Morphological, Anatomical, and Physiological Responses of Po_§_ pratensisL. 'Merion' and Festuca rubr___a__ L. Pennlawn' to Reduced Light Intensities presented by James Freeman Wilkinson has been accepted towards fulfillment of the requirements for Ph.D. degree in Crop and Soil Sciences ? Win Major professor Date 14; _, J :2 .,, 7\3 \, 0-7639 BINDING av HMS & SEW 800K BINDERY INC. usmm BINDERS l Ila "" ' HIRI- ABSTRACT MORPHOLOGICAL, ANATOMICAL, AND PHYSIOLOGICAL RESPONSES OF POA PRATENSIS L. 'MERION' AND FESTUCA RUBRA L. 'PENNLAWN' TO REDUCED LIGHT INTENSITIES BY James Freeman Wilkinson Kentucky bluegrass (Poa pratensis L.) and red fescue (Festuca rubra L.) are both capable of adequate growth in full sun, whereas red fescue usually provides a more suitable turf in the shade. The objectives of this investigation were to characterize the morphological, anatomical, and photosynthetic-respiratory responses of Merion Kentucky bluegrass and Pennlawn red fescue to re- duced light intensities. It was anticipated this infor- mation might elucidate the shade adaptive mechanisms of red fescue. Light intensities of 2.7, 5.4, 10.8, 21.5, and 43 klux were established in separate growth chambers. Light quality, soil moisture, and soil temperature were standardized among growth chambers. James Freeman Wilkinson Morphological Responses Leaf length of both cultivars increased with de- creasing light intensity to 10.7 klux, but decreased at intensities below 10.7 klux. Each cultivar had narrower leaves with successive reductions in light intensity. Shoot angle was measured on plants grown singly. Both cultivars displayed a horizontal growth habit at high light intensities. The red fescue remained relatively horizontal under low light, whereas the Kentucky blue— grass exhibited a vertical growth habit. Both cultivars responded similarly in terms of clipping, dry weight, leaf area, percent moisture, and chlorophyll content. Clipping weights decreased, and percent moisture increased under low light intensities. Clipping leaf area was greatest at 10.7 klux, and de- creased at higher or lower light intensities. Chlorophyll/dm2 decreased, but chlorophyll/g increased as light intensity was reduced. Plant shoots and roots were separated following the final clipping. Shoot and root growth decreased under lower light intensities. However, the red fescue produced greater shoot weight than the Kentucky bluegrass under the 2 James Freeman Wilkinson lowest intensity, whereas the Kentucky bluegrass was superior at the highest light intensity. The Kentucky bluegrass produced less leaf area, fewer shoots/cmz, and fewer tillers/plant with each decrement of lower light, while the red fescue produced equal numbers in these cate- gories through 5.4 klux. Thus, Pennlawn red fescue was superior to Merion Kentucky bluegrass at low light inten- sities only in terms of shoot growth below the cutting height (verdure). Anatomical Responses Pennlawn red fescue displayed greater cuticle, vascular, and support tissue development at low light intensities. Stomatal density of both cultivars decreased under reduced light. Stomatal pore length did not vary with light intensity. Chloroplast density decreased with reduced light intensity for both cultivars. The distribution of chloro- plasts was not affected by light intensity. The Kentucky bluegrass displayed increased thylakoid and grana stack development at reduced light intensity, whereas the red fescue chloroplast ultrastructure remained unchanged. 3 James Freeman Wilkinson Shade adaptation of Pennlawn red fescue may be related to greater development of the cuticle, vascular, and support tissues, and chloroplast ultrastructure. Stomatal and chloroplast size and distribution responses of the two cultivars to reduced light intensity were similar, and'cannot be associated with the ability of Pennlawn red fescue to provide a more desirable turf than Merion Kentucky bluegrass in the shade. Photosynthetic—Respiratory Responses Infrared CO2 analysis was used to measure assimi- lation rates of swards and individual plants. Both cul- tivars displayed decreased net photosynthesis (PN) and dark respiration (RD), lower light saturation levels, and lower light compensation points when grown under reduced light intensity. Swards generally had lower PN and RD rates, but higher light saturation levels and light com- pensation points than the individual plants. Both cultivars responded similarly to reduced light intensity in terms of PN, light saturation levels, and light compensation points. These factors could not James Freeman Wilkinson be associated with the ability of Pennlawn red fescue to provide a more desirable turf than Merion Kentucky blue- grass in the shade. RD of individual plants of the red fescue was reduced at the lowest light intensity, whereas the RD of the Kentucky bluegrass was not. This response may contribute to the positive CO2 balance of the red fescue at reduced light intensities, and thus to its shade adaptability. MORPHOLOGICAL, ANATOMICAL, AND PHYSIOLOGICAL RESPONSES OF POA PRATENSIS L. 'MERION' AND FESTUCA RUBRA L. 'PENNLAWN' TO REDUCED LIGHT INTENSITIES BY James Freeman Wilkinson A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Crop and Soil Sciences 1973 To my wife Cheryl for her love and understanding through my years of graduate study. ii ACKNOWLEDGEMENTS The author would like to express his gratitude to Dr. James B. Beard for his guidance and assistance throughout my graduate program. Special thanks are also given to Dr. Paul Rieke, Dr. Donald Penner, Dr. F. W. Snyder, and Dr. Joseph Vargas for their assistance in the completion of this investigation. iii TABLE OF CONTENTS LIST OF TABLES . . . . . . . . . . . . . . . . LIST OF FIGURES O O O O O O O O O O O O O O 0 INTRODUCTION . . . . . . . . . . . . . . . . . POA PRATENSIS L. 'MERION' AND FESTUCA RUBRA L. 'PENNLAWN' AT REDUCED LIGHT INTENSITIES: I. MORPHOLOGICAL RESPONSES. . . . . . . . . Abstract . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . Materials and Methods. . . . . . . . . Results 0 O O I O O O O O O O C C O O 0 Discussion . . . . . . . . . . . . . . References . . . . . . . . . . . . . . POA PRATENSIS L. 'MERION' AND FESTUCA RUBRA L. 'PENNLAWN' AT REDUCED LIGHT INTENSITIES: II. ANATOMICAL RESPONSES. . . . . . . . . . Abstract 0 O O O O O O O O O O O O O O IntrOduction O O O O O O O O O O O O 0 Materials and Methods. . . . . . . . . iv Page vi viii 10 16 20 23 33 33 35 38 TABLE OF CONTENTS (cont.) Page Results and Discussion . . . . . . . . . . . 43 References . . . . . . . . . . . . . . . . . 48 POA PRATENSIS L. 'MERION' AND FESTUCA RUBRA L. 'PENNLAWN' AT REDUCED LIGHT INTENSITIES: III. PHOTOSYNTHETIC-RESPIRATORY RESPONSES . . . . 65 Abstract . . . . . . . . . . . . . . . . . . 65 Introduction . . . . . . . . . . . . . . . . 67 Materials and Methods. . . . . . . . . . . . 72 Results and Discussion . . . . . . . . . . . 77 Conclusions. . . . . . . . . . . . . . . . . 82 References . . . . . . . . . . . . . . . . . 84 CONCLUSIONS. . . . . . . . . . . . . . . . . . . . . 91 LITERATURE CITED . . . . . . . . . . . . . . . . . . 96 Table 1.1. 11.1. II.2. II.3. 11.4. II.5. LIST OF TABLES Shoot angle of singly grown plants of Merion Kentucky bluegrass and Pennlawn red fescue at five light intensities. Vertical = 0°, horizontal = 90°. . . . The percentages of total cross sectional leaf area composed of epidermal, meso- phyll, vascular, and support tissues of Merion Kentucky bluegrass and Pennlawn red fescue grown at three light inten- Sities O O O O O O O O O I O O O O I 0 Number of stomata/mm2 on the adaxial and abaxial leaf surfaces of Merion Kentucky bluegrass and Pennlawn red fescue grown at three light intensities . . . . . . Stomatal pore length (microns) on the adaxial leaf surface of Merion Kentucky bluegrass and Pennlawn red fescue grown at three light intensities . . . . . . Percent of chloroplast cross sectional area composed of grana stacks of Merion Kentucky bluegrass and Pennlawn red fescue grown at two light intensities. Thylakoids per grana stack of Merion Kentucky bluegrass and Pennlawn red fescue grown at two light intensities. vi Page 25 50 51 52 53 54 LIST OF TABLES (cont.) Table IIIii. III.2. IIIO3. Page Net photosynthesis (PN) measured at pre- conditioning light intensity and dark respiration (RD) of swards and individual plants of Merion Kentucky bluegrass and Pennlawn red fescue grown at three light intensities. . . . . . . . . . . . . 87 Light saturated net photosynthetic rate (PN) of swards and individual plants of Merion Kentucky bluegrass and Pennlawn red fescue at three light intensities. . . 88 Light saturation levels and light compen- sation points of swards and individual plants of Merion Kentucky bluegrass and Pennlawn red fescue grown at three light intensities. . . . . . . . . . . . . . . . 89 vii LIST OF FIGURES Figure 1.1. Spectral distribution within the growth chambers . . . . . . . . . . . . . . . . . 1.2. (A) Average leaf length (cm) above cutting height, and (B) leaf width measured on the youngest, fully expanded leaf 1 cm from the collar prior to weekly clipping of Merion Kentucky bluegrass and Penn- lawn red fescue grown at five light intensities. Leaf widths are placed into classes . . . . . . . . . . . . . . . 1.3. (A) Clipping dry wt. (mg/pot) above 5 cm after 1 week's regrowth, and (B) clipping percent moisture on a fresh weight basis of Merion Kentucky bluegrass and Pennlawn red fescue grown at five light intensities 1.4. (A) Leaf area (cm2) of clippings collected above 5 cm after 1 week's regrowth, and (B) leaf area (dmz) below 5 cm 14 weeks after germination of Merion Kentucky blue- grass and Pennlawn red fescue grown at five light intensities . . . . . . . . . . 1.5. (A) Milligrams total chlorophyll/dmz, and (B) mg chlorophyll/g dry wt. of clippings of Merion Kentucky bluegrass and Pennlawn red fescue grown at five light intensities. . . . . . . . . . . . . . viii Page 26 27 28 29 30 LIST OF FIGURES (cont.) Figure I.6. II.1. II.2. II.3. 11.4. 11.5. III.1. (A) Shoot dry wt. (g/pot) below 5 cm, and (B) root dry wt. (g/pot) 14 weeks after germination of Merion Kentucky bluegrass and Pennlawn red fescue grown at five light intensities. . . . . . . . . . . . (A) Shoots/cmz, and (B) average number of tillers/plant 14 weeks after germination of Merion Kentucky bluegrass and Pennlawn red fescue grown at five light intenSitieSo O O O O O O O O O O O O O O Merion Kentucky bluegrass (A) and Pennlawn red fescue (B) leaf cross sections grown at 10.8 klux. Note the well defined cuticle layer of red fescue. X40. . . . Merion Kentucky bluegrass leaf cross sections grown at 43 (A) and 2.7 (B) klux X400 0 O O O O O O O O O O O O O O I O O Pennlawn red fescue leaf cross sections grown at 43 (A) and 2.7 (B) klux. X400. Transmission electron micrographs of Merion Kentucky bluegrass chloroplasts grown at 43 (A) and 2.7 (B) klux. X21,000. . . . Transmission electron micrographs of Penn- lawn red fescue chloroplasts grown at 43 (A) and 2.7 (B) klux. X21,000 . . . . . Comparison of the spectral distribution in the assimilation chamber and growth Chalmers O O O O O O O O O I O O O O O 0 ix Page 31 32 55 57 61 63 90 INTRODUCTION Maintenance of an attractive turf in shade presents numerous difficulties for even the most skilled profes- sional turfmen. A 1966 Pennsylvania survey of 326 golf. courses indicated growing turf in shade to be the number one management problem (12). It has been estimated 20% of the turf grown in the U.S. is subjected to some degree of shade (3). Kentucky bluegrass (Poa pratensis L.), the most widely grown cool season turfgrass, has not performed satisfactorily in shade in the past (4, 19). Red fescue (Festuca rubra L.), on the other hand, is capable of pro- viding a more suitable turf in shade. It would be desir- able to more fully understand the shade adaptive mechanisms of red fescue. If the mechanisms were elucidated, it may be possible to rapidly screen turfgrass species and culti- vars for shade tolerance. The objectives of this investigation were to study the morphological, anatomical, and photosynthetic-respiratory responses of Merion Kentucky bluegrass and Pennlawn red fescue to reduced light intensity. Each aspect was studied individually, and the results are presented in three sep- arate sections. It was anticipated this information might elucidate some of the shade adaptive mechanisms of red fescue. Factors affecting the growth of turf in shade besides light intensity (light quality, soil moisture, disease, tree roots) were controlled or eliminated. POA PRATENSIS L. 'MERION' AND FESTUCA RUBRA L. 'PENNLAWN' AT REDUCED LIGHT INTENSITIES: I. MORPHOLOGICAL RESPONSES ABSTRACT The objectives of the study were to characterize the morphological responses of Kentucky bluegrass and red fescue to reduced light intensity. Merion Kentucky blue- grass and Pennlawn red fescue were grown in separate growth chambers under light intensities of 2.7, 5.4, 10.7, 21.5, and 43 klux. Light quality, soil moisture, and soil tem- perature were standardized among chambers. Plants were clipped weekly at 5 cm for 14 weeks. Leaf length and width were determined prior to clipping. Leaf length of both cultivars increased with decreasing light intensity to 10.7 klux, but decreased at intensities below 10.7 klux. Each cultivar had nar- rower leaves with successive reductions in light intensity. Shoot angle was measured on plants grown singly. Both cultivars displayed horizontal growth at high light inten- sity. The red fescue remained relatively horizontal under low light intensities, whereas the Kentucky bluegrass ex- hibited a vertical growth habit. 3 Clipping weight, percent moisture, leaf area, and chlorophyll content were determined after clipping. Both cultivars responded similarly. Clipping weights decreased, and percent moisture increased under lower light inten- sities. Clipping leaf area was greatest at 10.7 klux, and decreased at higher or lower light intensities. Chloro- phyll/dm2 decreased, but chlorophyll/g increased as light intensity decreased. The Kentucky bluegrass was comparable to the red fescue under low light intensity in all four of the above categories. Plant shoots and roots were separated following the final clipping. Shoot and root production decreased under lower light intensities. However, the red fescue produced greater shoot weight than the Kentucky bluegrass under the lowest intensity, whereas the Kentucky bluegrass was su- perior at the highest light intensity. The Kentucky blue- grass produced less leaf area, fewer shoots/cmz, and fewer tillers/plant with each decrement of lower light, whereas the red fescue produced equal numbers in these categories through 5.4 klux. Thus, Pennlawn red fescue was superior to Merion Kentucky bluegrass at low light intensities only in terms of shoot growth below the cutting height (verdure). The superiority of red fescue under shade has been related to competition with tree roots, and the loss of Kentucky bluegrass due to disease infestation. These factors were not present in this study. Since the red fescue produced superior verdure under low light inten- sities, it must possess additional shade adaptation mechanisms. INTRODUCTION Both Kentucky bluegrass (Poa pratensis L.) and red fescue (Festuca rubra L.) form high quality turfs in full sun, but red fescue generally provides a more desirable turf under shaded conditions (3, 5). Maintenance of turf in shade presents unique problems. A 1966 Pennsylvania survey of 326 golf courses indicated growing turf in shade to be the number one turf problem (4). It has been esti- mated 20% of the turf grown in the U.S. is subjected to some degree of shade (2). The morphological responses of grasses associated with reduced light intensities include: decreased shoot, root, rhizome, and stolon growth; reduced shoot density and tillering; decreased root to shoot ratio; thinner leaves; longer internodes; increased leaf length; and upright growth habit (3). Lighter green color and in- creased succulence also have been found under low light intensities. A comprehensive study comparing the morpho- logical responses of Kentucky bluegrass and red fescue to reduced light intensity has not been made. 6 WOod (12) compared the growth of eight Kentucky bluegrass and eight red fescue cultivars in a controlled climate chamber study under light intensities from 2.4 to 32.3 klux. Shoot and root growth of both species was comparable at 16.2 and 32.3 klux. Red fescue cultivars generally outperformed Kentucky bluegrass cultivars at 2.4 and 5.4 klux. Wood reported both species responded to reduced light intensities by more flaccid, paler green, and narrower leaf blades. A field study also showed red fescue cultivars superior to Kentucky bluegrass cultivars in the shade. 'Beard (1) grew several turfgrass species and mixtures beneath shade trees. Red fescue was superior to Kentucky bluegrass in terms of turfgrass quality rat- ings and shoot density counts. Red fescue-Kentucky blue- grass mixtures were predominantly red fescue after two years. Wilson (11) grew red fescue, orchardgrass (Dactylis glomerata L.) and white clover (Trifolium repens L.) at light intensities of 2.2, 6.5, and 19.4 klux. Growth of orchardgrass and clover was reduced with each decrement of reduced light intensity. Red fescue grew as well at 6.5 as at 19.7 klux, indicating greater tolerance to reduced light intensities than orchardgrass or clover, but was seriously impairedat 2.2 klux. Many aspects of the shade environment in addition to reduced light intensity affect turfgrass growth: al- tered light quality, moderation of temperature extremes, increased disease incidence, decreased wind movement and evapotranspiration, and tree root competition (3). The adaptive mechanisms of shade tolerant species may involve acclimation to these factors. Beard (1) has shown red fescue more disease tolerant than Kentucky bluegrass under shaded conditions. Although the red fescue was thinned by Helminthosporium leafspot in its first year of growth, a more suitable turf resulted in subsequent years. Ken- tucky bluegrass was unable to survive due to powdery mildew (Erysiphe graminis D.C.). Whitcomb (9) compared the clipping yields of Kentucky bluegrass, red fescue, rough bluegrass (Poa trivialis L.), and perennial ryegrass (Lolium perenne L.) beneath shade trees, with and without tree root competition. Kentucky bluegrass shoot growth was impaired more by the tree roots than the other species. Whitcomb and Roberts (10) demonstrated Kentucky bluegrass rooting to be severely restricted by trees having shallow feeder roots. The objectives of this study was to characterize the morphological responses of Merion Kentucky bluegrass and Pennlawn red fescue to reduced light intensities. Other factors influencing turfgrass growth in shade (a1- tered light quality, disease incidence, soil temperature and moisture levels, tree root competition) were elimi- nated. It was anticipated this information might give further insight into shade adaptation mechanisms of red fescue. MATERIALS AND METHODS £1.92; Light intensities of 2.7, 5.4, 10.7, 21.5, and 43 klux (1.4, 2.4, 5.0, 7.5, and 11.4 x 103 uw cm-Z, re- spectively) were established in separate growth chambers. Preliminary studies indicated 2.7 klux was the lowest light intensity at which Merion Kentucky bluegrass could persist. A Weston Illumination Meter, Model 765, and a YSI-Kettering, Model 65 Radiometer were used for the light measurements. A 14 hr photoperiod was used. Light quality was first standardized among the chambers utilizing similar make bulbs and the same propor- tion of fluorescent to incandescent bulbs. An ISCO, Model SR Spectroradiometer indicated only slight variation in light quality among chambers. The variation in light quality within each chamber was not significant. The light was weak in the red and blue regions, strong in the green and infrared (Figure I.l). A similar light quality has been found beneath deciduous tree canopies (8). 10 11 Light intensities were established by raising and lowering chamber shelves. Plant material at 43 klux was within 0.50 m of the bulbs. Leaf temperature, measured with a Stoll-Hardy, Model HL4 Radiometer, and canopy tem- perature, measured with a copper/constantan thermocouple and potentiometer, were no more than 2 C above the soil temperature. Separate growth chambers were used for each light intensity in order to establish uniform soil temperatures, and to avoid the use of shading materials or screens which may significantly alter the turfgrass microenvironment. Light intensity varied markedly within each chamber, with variation increasing toward the chamber sides. All plant material was kept close to the center of the chamber, and was rotated every other day. E211. A sandy loam soil mix was used. Soil temperatures were maintained at 20 C, and were monitored using a bulb thermometer inserted 5 cm into the soil. Uniform soil moisture was maintained utilizing 1.25 cm tensiometers (Irrometer Company, Riverside, Cali- fornia). The tensiometers were inserted into pots seeded 12 with Kentucky bluegrass. Data were not taken from these pots. Soil moisture levels were monitored with the tensio- meters, and all pots watered accordingly. All pots were saturated weekly with a complete Hoagland's solution (6). Plant Material Merion Kentucky bluegrass and Pennlawn red fescue were seeded in 10 cm diameter (12 cm depth) plastic pots at 3 seeds/cmz. Seeds were germinated in a greenhouse. Three replications of each cultivar were placed under each light intensity when the seedlings were 1 cm in height. Additional pots were thinned to one seed per pot for shoot angle determinations. Parameters Measured After plants reached 5'cm in height, clippings above 5 cm were collected weekly using hand clippers with a collection pan attached. Several measurements were made prior to weekly clipping. (a) Average leaf length above the 5 cm cutting height. (b) Leaf width was measured on the youngest fully expanded leaf, 1 cm from the leaf collar. Leaf widths were placed into classes of 0-0.5, 0.5-1, l-l.5, 1.5-2, and > 2 mm. Three measurements were 13 taken for each replication. (c) Shoot angle. Shoot angle was difficult to estimate on plants within an established turf. Pots with a single plant were included under each light intensity. Shoot angle determinations were made prior to weekly clipping at 5 cm, vertical being 0°, hori- zontal 90°. Leaf clippings were collected and placed in plastic bags to prevent desiccation. Several parameters were mea- sured. (d) Total fresh weight. (e) Leaf area. A 10 to 20 leaf subsample was taken from the fresh clippings. Fresh weight was determined, the leaves taped to paper, and a photocopy made. Leaf area of the subsample was then esti- mated using a planimeter. The leaf area: leaf weight ratio established for the subsample was used to estimate the total clipping leaf area. The estimate included only one leaf surface. (f) Chlorophyll content. A second subsample (approximately 1 g) was removed from the fresh clipping sample, weighed, placed in a flask, and covered with 50 ml of methanol. The flasks were stoppered and left in a dark cabinet overnight. Samples were then ground for two minutes in a Virtis Mixer, Model 45, filtered under vacuum, and brought to a volume equivalent to 1 liter. Absorbancy was measured at 650 and 665 nm with a l4 Perkin-Elmer, Model 27 Spectrophotometer. MacKinney's (7) formula for total chlorophyll in methanol solutions was utilized. Chlorophyll was expressed as mg/dm2 and mg/g dry weight. (9) Dry weight. The remaining fresh clippings were weighed, dried at 70 C, and reweighed. Dry weight was determined including subsamples taken for leaf area and chlorophyll estimations. (h) Percent moisture on a fresh weight basis was determined. The final clipping was made 14 weeks after germina- tion. All plants were cut off at the soil surface and several parameters determined. (i) Total fresh weight. (j) Number of shoots/pot. (k) Number of tillers/plant. (1) Leaf area, determined using the same technique de- scribed for clipping leaf area. (m) Dry weight, determined as previously described. (n) Root dry weight. Four sub- samples were removed from each pot, using a 1.5 cm circular soil sampling device. The soil and roots were dried at 70 C, ashed at 500 C, and reweighed. The loss in weight, corrected for the original soil organic matter content, was taken as root weight. The sides and bottom of the pots were avoided when the soil samples were taken. 15 Statistical Analysis A completely randomized block analysis of variance was made on the two cultivars at each light intensity. The determined variances at each light intensity were pooled, and a single LSD value (.05 level) was determined for each parameter measured. RESULTS Clippings were collected weekly between the 5th and 14th week following germination. Cultivar responses to reduced light intensities were similar throughout this period. Results presented are those obtained during the 11th week. Leaf length above the cutting height increased with decreasing light intensity to 10.7 klux (Figure 1.2). Leaf length decreased at the two lower light intensities. Al- though both cultivars responded similarly, the red fescue leaf length was less than the Kentucky bluegrass at any one light intensity. Leaf width (Figure 1.2) decreased with each decrement of decreasing light. The response of the two cultivars was similar. Shoot angle measurements are shown in Table 1.1. The angle measured was the angle of the shoot from the vertical. Both cultivars displayed a horizontal growth habit at the higher light intensities. The Kentucky blue- grass had an upright growth habit under low light inten- sities,whereastflmared fescue remained relatively horizontal. 16 17 Both cultivars responded similarly in clipping dry weight and percent moisture (Figure I.3). Clipping dry weight was maintained under decreasing light intensity to 10.7 klux, but declined rapidly below 10.7 klux for both cultivars. The Kentucky bluegrass produced more leaf growth than the red fescue at light intensities greater than 10.7 klux, but there was no difference below 10.7 klux. Percent moisture of both cultivars increased with each decrement of reduced light, ranging from 68% at 43 klux, to 83% at 2.7 klux. Clipping leaf area (Figure 1.4) increased with decreasing intensities to 10.7 klux, and then decreased under lower light intensities. The increased leaf area was due to the extended leaf length. The Kentucky blue- grass had a greater clipping leaf area than the red fescue above 10.7 klux, whereas the two cultivars did not differ below 10.7 klux. Both cultivars responded similarly in terms of chlorophyll content (Figure I.5). Chlorophyll/dm2 de- creased with decreasing light intensities. This decrease corresponded with the lighter green color of leaves ob- served at the lower light intensities. Chlorophyll/g dry 18 wt. increased with each decrement of decreasing light intensity. Dry shoot weight below the cutting height and root weight are shown in Figure I.6. While shoot growth of the Kentucky bluegrass was greater than the red fescue at the highest light intensity, the red fescue outperformed the Kentucky bluegrass at the lowest intensity. Root growth was reduced under low light (Figure I.6). No difference could be found in the root production between the two cultivars. The most marked reduction in the root-shoot ratio occurred between 43 and 21.5 klux for both cul- tivars. Merion Kentucky bluegrass had decreased leaf area below the cutting height with each decrement of reduced light intensity (Figure I.4). Pennlawn red fescue main- tained leaf area under decreasing light to 10.7 klux. Although leaf area of the red fescue decreased below 10.7 klux, the reduction was less for the red fescue than the Kentucky bluegrass at 2.7 and 5.4 klux. The shoot density of the Kentucky bluegrass de— clined below 21.5 klux, whereas shoot density of the red fescue did not decline until the light intensity was lower 19 than 5.4 klux (Figure I.7). Tillering of the Kentucky bluegrass was severely restricted at light intensities below 21.5 klux (Figure I.7). Tillering of the red fescue did not appear to be affected by light intensities as low as 5.4 klux. DISCUSSION Merion Kentucky bluegrass and Pennlawn red fescue responded differently to reduced light intensity in terms of shoot weight and leaf area below the cutting height, tillers/plant, shoot density, and leaf angle. The red fescue produced superior verdure at the lower light in- tensities, thus providing a more suitable turf. Shoot density and tillering of the red fescue did not decline until light intensities were below 5.4 klux. Perhaps more shade tolerant ground cover species should be used at light intensities below 5.4 klux if there is no sunfleck- ing. The Kentucky bluegrass displayed an upright growth habit under low light intensities, whereas the red fescue remained relatively horizontal. A shade adaptive mechanism of red fescue may be involved. The more horizontal growth habit of red fescue shoots may enhance light interception within the shade environment. Also, less photosyntheti- cally active, young leaf tissue will be removed by mowing. 20 21 The two cultivars responded similarly to reduced light intensities in the following parameters: leaf length, leaf width, clipping area, clipping yield, per- cent moisture, chlorophyll content, and root growth. The Kentucky bluegrass was superior at the higher light inten- sities in terms of leaf length, clipping weight, and clip- ping leaf area. Although the red fescue provided a better turf than the Kentucky bluegrass in shade, the Kentucky bluegrass was comparable to the red fescue at low light intensities in terms of vertical shoot growth above the cutting height and root production. The marked increase in percent moisture of leaf tissue within the shade environment may contribute to increased disease susceptibility. Plant factors besides succulence must be involved in disease susceptibility, since the response of both cultivars was similar. Red fescue does possess more disease resistance in shade than Kentucky bluegrass (1). Disease resistance and the ability to compete with tree roots have been studied as possible explanations for the favorable shade adaptation characteristics of red fescue (l, 9, 10). Tree root competition was not a factor in this investigation, and disease was not observed at any 22 time. Red fescue must possess additional shade adaptive mechanisms. These mechanisms may involve anatomical re- sponses, photosynthetic efficiencies, and respiration rates. 6. REFERENCES Beard, J. B. 1965. Factors in the adaptation of turfgrasses to shade. Agron. J. 57:457-459. Beard, J. B. 1967. Shade tolerance and maintenance. 38th International Turfgrass Conf. Proc. pp. 31-39. Beard, J. B. 1973. Turfgrass: Science and Culture. Prentice-Hall, Inc., Englewood Cliffs, N.J. pp. 181-209. Boster, D. O. 1966. Pennsylvania turfgrass survey, 1966. Penn. Crop Rept. Serv., Penn. Dept. Agr., Harrisburg. 38 pp. Hanson, A. A., and F. V. Juska, Ed. 1969. Turfgrass Science. Amer. Soc. Agron., Madison, Wisc. pp. 27-79. Hoagland, C. R., and D. I. Arnon. 1950. The water culture method for growing plants without soil. Calif. Agr. Exp. Sta. Circ. 374. pp. 32. MacKinney, G. 1941. Absorption of light by chloro- phyll solutions. J. Biol. Chemistry. 140:315-322. Vezina, P. E., and D. W. K. Boulter. 1969. The spec— tral composition of near ultraviolet and visible radiation beneath forest canopies. Can. J. Bot. 44:1267-1284. Whitcomb, C. E. 1972. Influence of tree root compe- tition on growth response of cool-season turf- grasses. Agron. J. 64:355-359. 23 10. ll. 12. 24 Whitcomb, C. E., and E. C. Roberts. 1973. Competi- tion between established tree roots and newly seeded Kentucky bluegrass. Agron. J. 65:126-129. Wilson, D. B. 1962. Effects of light intensity and clipping on herbage yields. Can. Jour. Plant Sci. 42:270-275. WOod, G. M. 1969. Evaluating turfgrasses for shade tolerance. Agron. J. 61:347-352. 25 TABLE I.l.--Shoot angle of singly grown plants of Merion Kentucky bluegrass and Pennlawn red fescue at five light intensities. Vertical = 0°, horizontal = 90°. LSD = 12.6. Light intensity, Shoot angle (degrees) lux X 103 Kentucky bluegrass Red fescue 2.7 20 38 5 4 25 55 10.7 30 60 21.5 70 70 43.1 75 80 26 .mumnsmao assess 4:» saunas coausnaupmae Hmupomamu-.H.H .mam ' I , r. b . 2.5 A 00h 00m 000 00¢ 0. $92510 3325 I: 8 on O? on L OD .-wu .-uJo MT’ 27 6F a ILSD=O.56 LEAF WIDTH, mm class i o 1 l l L I l 7 3 7 A I LSD=O.47 E 6 - i 5 — BLUEGRASS £3 ’1' ‘y\ m 4 I— I \~~ .l ~~ u ‘”~ 4 I‘ m 3)- ..n ‘b o 27] l 1 1 . IO.7 2|.5 4 . 54 3' LIGHT INTENSITY, m x I03 Fig. I.2.--(A) Average leaf length (cm) above cutting height, and (B) leaf width measured on the youngest, fully expanded leaf 1 cm from the collar prior to weekly clipping of Merion Kentucky bluegrass and Pennlawn red fescue at five light intensities. Leaf widths were placed into classes. 28 U 80- a: ILSD= 3.82 D - g. « 2 B = 0 75- x z — BLUEGRASS ._ — —FESCUE z - 3 m 70- Iu ‘~ 0. ' 65 ' l l J F ; 400 O E .3 300 3 ). a: ‘3 200 (D E O. E 4 mo 0 O l J I I | z? 4 no: 2L5 43y LIGHT INTENSITY, In: x :03 ——_—— ,_—_~ .v w.__- — Fig. I.3.--(A) Clipping dry wt. (mg/pot) above 5 cm after 1 week's regrowth, and (B) clipping percent moisture on a fresh weight basis of Merion Kentucky blue- grass and Pennlawn red fescue at five light intensities. 29 ILSD'l I.58 LEAF AREA sELow 5cm, am2 0 I — BLUEGRASS — - FESCUE N S _ I LSD 8 23.85 4 LI] K < IL < III .I \ -- . g _— — :— E E .I 0 I I I 2.7 10.7 2|.5 43.| 5.4 LIGHT INTENSITY, lux X IO3 Fig. I.4.--(A) Leaf area (cm2) of clippings col- lected above 5 cm after 1 week's regrowth, and (B) leaf area (dmz) below 5 cm 14 weeks after germination of Merion Kentucky bluegrass and Pennlawn red fescue at five light intensities. 30 T l VTI ' l ' I I l I I I I I I mg CHLOROPHYLL lgm DRY WI CLIPPINGS K: 1 I0 I s I —BLUEGRASS i 6 ——-FESCUE ; o l l l I 4 I i U) I <9 I E __. .‘ 0- fl . E _’ - - -- - — --- 0 N E ‘U I \ ' .l g 1 L80 - 0.72 I a. O m 0 _,| I- I 0 r O I E ’1 L 1 l 4 2.7 IO.7 2|.5 43.! f 5.4 i LIGHT INTENSITY, In x Io3 -———~— »— —-———--— —-- -m— ,, ——- —-v -- - — *-> - -—— Fig. I.5.--(A) Milligrams total chlorophyll/dmz, and (B) mg chlorophyll/g dry wt. of clippings of Merion Kentucky bluegrass and Pennlawn red fescue grown at five light intensities. ' 31 I IZF I Ir B c—BLUEGRASS '0 " --FESCUE E O a h- i-’ . 3 >- .— m 6 ° L .— o 4__ ’ 0 LSD - 2.49 (I: L b I I i 2 I— o L l l l J 5L F-—--- —- I LSD -o.52 SHOOT DRY W12, gm 0' l l l 2.7 IO.7 2|.5 43. I 5.4 LIGHT INTENSITY, m x lo3 F_‘—'———‘ . _.___. _ 7 , . w,___V_.~— Fig. I.6.--(A) Shoot dry wt. (g/pot) below 5 cm, and (B) root dry wt. (g/pot) 14 weeks after germination of Merion Kentucky bluegrass and Pennlawn red fescue at five light intensities. 32 ’--------- 'HLLERS/PLANT LSD=L06 — BLUEGRASS — — FESCUE SHOOTS/cmz OI LSD=LO3 o J l l l J 2.7 l0.7 2|.5 43.| 5.4 LIGHT INTENSITY, In: x I03 Fig. I.7.--(A) Shoots/cmz, and (B) average number of tillers/plant 14 weeks after germination of Merion Kentucky bluegrass and Pennlawn red fescue grown at five light intensities. POA PRATENSIS L. 'MERION' AND FESTUCA RUBRA L. 'PENNLAWN' AT REDUCED LIGHT INTENSITIES: II. ANATOMICAL RESPONSES ABSTRACT The objectives were to characterize the anatomical responses of Kentucky bluegrass and red fescue to reduced light intensities. Merion Kentucky bluegrass and Pennlawn red fescue were grown in separate growth chambers at light intensities of 2.7, 10.8, and 43 klux. Light quality, soil moisture, and soil temperature were standardized among growth chambers. Anatomical studies were conducted on the youngest, fully expanded leaf. The red fescue had more developed cuticle, vascular, and support tissues at low light intensities. Cuticle development in red fescue at low light intensity may be an important consideration in disease resistance. Stomatal density of both cultivars decreased under reduced light intensity. Stomatal pore length did not vary with light intensity. Chloroplast density decreased with reduced light intensity for both cultivars. The distribution of chloroplasts was not affected by light intensity. The Kentucky bluegrass had increased thylakoid and grana stack 33 34 development at reduced light intensity, whereas the red fescue chloroplast ultrastructure remained unchanged. Shade adaptation of red fescue may be related to development of cuticle, vascular, and support tissue, and to chloroplast ultrastructure. Stomatal and chlorOplast size and distribution responses of the two cultivars to reduced light intensity were similar, and could not be associated with the ability of the red fescue to provide a more desirable turf than the Kentucky bluegrass in the shade. INTRODUCTION The superiority of red fescue (Festuca rubra L.) over Kentucky bluegrass (Poa pratensis L.) in providing a desirable turf in shade is well documented (2, 15). Loss of Kentucky bluegrass in the shade environment has been related to disease incidence (l) and tree root competi- tion (13, 14). Reduced light intensity alters the anatomy of plants in numerous ways: thinner, narrower leaf blades (3, 4, 6, 7, 11); less cross sectional leaf area (6, 7, 10); thinner mesophyll (3, 6, 10, 11); smaller epidermal cells (6, 8); thinner cell walls (8); reduced vascular tissue development (4, 5, 6, 11); changes in stomata fre— quency and size (3, 4, 11); and alteration of chloroplast size and structure (3, 4, 5, 8). Reductions in light intensity generally decrease stomata numbers, but increase their size (3, 11). CO2 transfer through larger stomata may compensate for de- creased density at reduced light intensities. However, 35 36 Bjorkman et al. (4) working with Atriplex patula L. at reduced light intensities, did not observe an increase in either stomata pore size or guard cell size. Goodchild, Bjorkman, and Phyliotis (8) observed more chloroplasts in the mesophyll cells adjacent to the upper epidermis in several rainforests species. Chloro- plasts also appeared to be large and dark green. Bjorkman et al. (4) found only half as many chloroplasts in leaf cross sections of A. patula under reduced light intensity. The chloroplasts appeared to be larger under low light intensities. Bjorkman and Holmgren (3) studied ecotypes of Solidago virgaurea L. from exposed and shaded habitats. The exposed ecotypes displayed normal chloroplast struc- ture under high and low light. In contrast, the shaded ecotypes had pale, irregular, fragmented chloroplasts when exposed to high light intensities. Cormack (5) observed the chloroplasts of exposed leaves of Vicia americana Muhl. to be discernable by either transmitted or phase-contrast illumination. The chloroplasts from shaded leaves were not visible using transmitted light, but were clearly defined using phase-contrast. He suggested there may be 37 a difference in the state of the cytoplasm in which the chloroplasts were embedded. Chloroplast ultrastructure appears to be altered at reduced light intensity. Goodchild et al. (8) found the chloroplasts of rainforest species to contain large, well developed grana stacks, with many thylakoids. The grana also appeared to be irregularly oriented, and not in one plane as usually found. Bjorkman et al. (4) found more thylakoids per grana stack in A, patula at reduced light intensity. He correlated decreased carboxydismutase activity with decreased volume of stroma per chloroplast. This may contribute to a decrease in the CO fixing capa- 2 bility under low light. The objectives of this investigation were to char- acterize the anatomical responses of Merion Kentucky blue- grass and Pennlawn red fescue to reduced light intensities. This information might elucidate some of the shadeeadaptation mechanisms of red fescue. Other shade associated factors influencing growth (altered light quality, disease inci- dence, soil temperature and moisture levels, tree root competition) were controlled or eliminated in this study.: MATERIALS AND METHODS The experimental conditions were similar to those described in an earlier study (15). Light A 14 hour photoperiod was used. Light intensities of 2.7, 10.8, and 43 klux (1.4, 5.0, and 11.4 x 103 uw cm. , respectively) were established in separate growth chambers. Both Merion Kentucky bluegrass and Pennlawn red fescue provided a good turf at 43 klux in an earlier study (15). The growth of the Kentucky bluegrass was im- paired at lOJBklux,whereas the red fescue still maintained a dense turf. Although neither cultivar performed well at 2.7 klux, the red fescue was superior to the Kentucky bluegrass in terms of verdure, leaf area, shoot density, and tillers per plant. Light quality was standardized for the three chambers utilizing similar bulbs and the same proportion of fluorescent to incandescent bulbs. An ISCO, Model SR 38 39 Spectroradiometer indicated only slight variations among or within chambers. The light was weak in the red and blue wavelengths, but strong in the green and infrared (15). Light intensities were established by raising and lowering chamber shelves. Plant material at 43 klux was within 0.50 m of the bulbs. Leaf temperature, measured with a Stoll-Hardy, Model HL4 Radiometer, and canopy tem- perature, measured with a copper/constantan thermocouple and potentiometer, were no more than 2 C above the soil temperature (maintained at 20 C). Separate growth chambers were used for each light intensity in order to establish uniform soil temperatures, and to avoid the use of shading materials or screens that can significantly alter the turfgrass microenvironment. Light intensity varied markedly within each chamber, with variation increasing toward the chamber sides. All plant material was kept in the center of the chamber, and the individual pots rotated every other day. Soil A sandy loam soil mix was uSed. Soil temperatures were maintained at 20 C, and were monitored using a bulb thermometer inserted 5 cm into the soil. Uniform soil 40 moisture was maintained utilizing 1.25 cm tensiometers (Irrometer Company, Riverside, California). The tensio- meters were inserted into separate pots seeded with Ken- tucky bluegrass. Soil moisture levels were monitored with the tensiometers, and all pots irrigated accordingly. All pots were saturated weekly with a complete Hoagland's solution. Plant Material Merion Kentucky bluegrass and Pennlawn red fescue were seeded in 10 cm diameter (12 cm depth) plastic pots at 3 seeds/cmz. Seeds were germinated in a greenhouse and placed under each light intensity when seedlings were 1 cm in height. Plants were mown periodically at S cm. Occa- sional applications of Karathané§>were made for powdery mildew (Erysiphe graminis D.C.) control. Plants were pre- conditioned for six weeks prior to sampling. Sampling lasted three weeks. Parameters Measured The youngest, fully expanded leaf was removed for sectioning. Fresh leaf tissue was sectioned using a Lab Line/Hooker Plant Microtome (9). The sections were fixed 41 with FAA, and stained with safranin-fast green. Sections were traced from photographs. The tracings were cut out and weighed to determine the relative proportions and size of epidermal, mesophyll, vascular, and support tissue. Stomatal density and size was determined using the method of Shearman and Beard (12). A nitrocellulose im- pression was made of the adaxial and abaxial surfaces of the youngest,fully expanded leaf. Stomata were observed at 400 X. Counts were taken randomly between the leaf edge and midvein. Chloroplast ultrastructure was observed with a transmission electron microscope. One mm2 sections were cut from the youngest,fully expanded leaf, and fixed in 5% glutaraldehyde in a 0.1 M_phosphate buffer. The sec- tions were subsequently fixed in 2% osmium tetroxide, dehydrated in an ethanol series, and embedded in an epoxy resin. The resin was polymerized at 50 C and sections cut 600-800 A°.thick. Chloroplasts were observed at 60 kv. Statistical Analysis Four replications of the cross sections, and eight of the stomatal impressions were used. A completely ran- domized block analysis of variance was made on the two 42 cultivars at each light intensity. The determined vari- ance at each light intensity was pooled, and a single LSD value (.05 level) was determined for each parameter mea- sured. RESULTS AND DI SCUS S ION Cuticle Both cultivars had a well defined cuticle at 43 klux, although the cuticle of the red fescue was about twice as thick as that of the Kentucky bluegrass. Leaf cross sections of the red fescue grown at 10.8 klux still had a well developed cuticle layer, whereas the cuticle of the Kentucky bluegrass was thin (Figure 11.1). Neither cultivar had a well developed cuticle layer at 2.7 klux. Disease infestation, particularly by powdery mildew, has been shown to be a major factor in the loss of Kentucky bluegrass in the shade (l). The ability of Pennlawn red fescue to produce a cuticle layer at reduced light intensities may contribute to disease resistance. Epidermis Both cultivars had thinner epidermal cells at reduced light intensities. The degree of reduction was similar for the two cultivars. 43 44 Leaf Tissues The percentages of the cross sectional leaf area, composed of epidermal, mesophyll, vascular, and support tissues, are shown in Table 11.1. Percent epidermal tissue increased, but mesophyll decreased under reduced light for both cultivars. The Kentucky bluegrass had a significant decrease in vascular and support tissue under decreased light, whereas the red fescue did not. Greater development of vascular and support tissues in Pennlawn red fescue at reduced light intensity may con- tribute to shade adaptation. Improved vascular tissue development may lead to more rapid movement of water, nu- trients, and photosynthate. Additional support tissue at reduced light intensity may impart increased wear tolerance. Stomata Both cultivars had decreased stomata density on the adaxial and abaxial leaf surfaces under reduced light (Table 11.2). The red fescue stomata density ranked lower than that of the Kentucky bluegrass at all light inten- sities. Stomata pore length did not vary with light in- tensity (Table 11.3), although the stomata of the red fescue were larger than those of the Kentucky bluegrass 45 at all light intensities. Stomata responses could not be related to the red fescue shade adaptation. Chloroplasts The number of chloroplasts per cross sectional unit area decreased under reduced light for both cultivars (Figures 11.2 and 11.3). This is in accordance with the decrease in chlorophyll/dm2 found earlier. Light intensity did not affect the distribution of chloroplasts within the cross sections. The chloroplasts of both cultivars grown at 43 klux were distinct when observed under the light microscope (Figures 11.2 and 11.3). Chloroplasts of the red fescue grown at 2.7 klux remained distinct (Figure 11.3), whereas the Kentucky bluegrass chloroplasts were not discernable when grown at the same light intensity (Figure 11.2). Cormack (5) made a similar observation in y. americana. Chloroplast ultrastructure was observed with a transmission electron microscope (Figures 11.4 and 11.5). The percent of chloroplast cross sectional area composed of grana stacks was significantly increased in Merion Kentucky bluegrass when grown at reduced light intensity (Table 11.4). The percentage did not increase 46 significantly in Pennlawn red fescue chloroplasts under low light. An increase in the number of thylakoids per grana stack was associated with the increased area of grana in the Kentucky bluegrass (Table II.5). This re- sponse has been found in other species at reduced light intensity (4, 8). Bjorkman et al. (4) correlated decreased carboxydismutase activity in A. pa:gla_with increased volume of grana (decreased volume of stroma). This could contribute to decreased CO2 fixing capacity under low light. In conclusion, Merion Kentucky bluegrass and Penn- lawn red fescue displayed many typical anatomical responses to reduced light intensity. The red fescue differed from the Kentucky bluegrass at reduced light intensities in terms of cuticle, vascular, and support tissue development, and chloroplast ultrastructure. These factors may play important roles in the shade adaptation of Pennlawn red fescue. Increased stomata size (3, 11) and altered chloro- plast distribution (8) also have been related to shade tolerance in other species. The responses of the two cultivars to these factors were similar, and they could not be associated with the ability of the red fescue to 47 provide a more desirable turf than the Kentucky bluegrass in the shade. REFERENCES Beard, J. B. 1965. Factors in the adaptation of turfgrasses to shade. Agron. J. 57:457-459. Beard, J. B. 1973. Turfgrass: Science and Culture. Prentice-Hall, Inc., Englewood Cliffs, N.J. pp. 181-209. Bjorkman, O" and P. Holmgren. 1963. Adaptability of the photosynthetic apparatus to light intensity in ecotypes from exposed and shaded habitats. Physiol. Plant. 16:889-914. Bjorkman, 0., N. K. Boardman, J. M. Anderson, S. W. Thorne, D. J. Goodchild, and N. A. Phyliotis. 1972. Effect of light intensity during growth of Atriplex patula on the capacity of photosynthetic reactions, chloroplast components, and structure. Ann. Rept. Dir., Dept. Pl. Biol., Carnegie Inst., 1971-1972. pp. 115-134. Cromack, R. G. H. 1955. Effects of extreme shade upon leaf form and structure in Vicia americana. Can. J. Bot. 33:293-297. Evans, P. S. 1964. A comparison of some aspects of the anatomy and morphology of Italian ryegrass (Lolium multifolium Lam.) and perennial ryegrass (L, perenne L.). New Zealand J. Bot. 2:120-130. Forde, B. J. 1966. Effects of various environments on the anatomy and growth of perennial ryegrass and cocksfoot. New Zealand J. Bot. 4:455-468. 48 10. 11. 12. 13. 14. 15. 49 Goodchild, D. J., O. Bjorkman, and N. A. Phyliotis. 1972. Chloroplast ultrastructure, leaf anatomy, and content of chlorophyll and soluble protein in rainforest species. Ann. Rept. Dir., Dept. P1. Biol., Carnegie Inst., 1971-1972. pp. 102-107. Hooker, W. J. 1967. A microtome for rapid prepara- tion of fresh sections of plant tissue. Phytopath. 57:1126-1129. Mitchell, K. J., and K. Soper. 1958. Effects of dif- ferences in light intensity and temperature on the I anatomy and development of the leaves of Lolium perenne and Paspalum dilatatum. New Zealand J. Agric. 1:1-16. Penfound, W. T. 1931. Plant anatomy as conditioned by light intensity and soil moisture. Am. J. Bot. 18:558-572. Shearman, R. C.,and J. B. Beard. 1972. Stomatal den- sity and distribution in Agrostis as influenced by species, cultivar, and leaf blade surface and posi- tion. Crop Sci. 12:822-823. Whitcomb, C. E. 1972. Influence of tree root compe- tition on growth response of cool-season turf- grasses. Agron J. 64:355-359. Whitcomb, C. E., and E. C. Roberts.’ 1973. Competition between established tree roots and newly seeded Kentucky bluegrass. Agronomy J. 65:126-129. Wilkinson, J. F., and J. B. Beard. 1973. £93 Egg: tensis L. 'Merion' and Festuca rubra L. 'Pennlawn' at reduced light intensity: I. Morphological responses. Proc. Sec. Intern. Turfgrass Res. Conf., in press, and this volume. 50 TABLE II.l.--The percentages of total cross sectional leaf area composed of epidermal, mesophyll, vascular, and support tissues of Merion Kentucky bluegrass and Pennlawn red fescue grown at three light intensities. Light % of cross section area Species intensity (klux) Epidermal Mesophyll Vascular Support 43 31.15 58.73 6.42 4.45 K t k en “C Y 10.8 34.86 57.09 5.67 2.39 bluegrass 2.7 39.29 55.53 3.45 1.36 43 21.40 68.00 5.89 4.70 Red 10.8 22.70 67.50 5.68 4.12 fescue 2.7 29.00 62.30 4.62 3.80 LSD (.05) 7.42 7.01 1.88 1.90 51 TABLE II.2.--Number of stomata/mm2 on the adaxial and abaxial leaf surfaces of Merion Kentucky bluegrass and Pennlawn red fescue grown at three light intensities. Stomata/mm2 S ecies Light intensity p (klux) leaf surface adaxial abaxial 43 208 88 KentUCkY 10.8 200 16 bluegrass 2.7 168 0 43 176 8 Red 10.8 128 8 fescue 2.7 104 0 LSD (.05) 38.5 16.8 52 TABLE II.3.--Stomata1 pore length (microns) on the adaxial leaf surface of Merion Kentucky bluegrass and Pennlawn red fescue grown at three light intensities. . Light intensity Stomatal length Spec1es . (klux) (microns) 43 26.8 KentUCky 10.8 26.3 bluegrass 2 7 25 9 43 35 6 Red 10.8 34.4 fescue 2.7 33.8 LSD (.05) 4.3 53 TABLE II.4.--Percent of chloroplast cross sectional area composed of grana stacks of Merion Kentucky bluegrass and Pennlawn red fescue grown at two light intensities. Species Light intensity Chloroplast area (klux) (% of grana stacks) 43 11.27 Kentucky bluegrass 2.7 29.48 43 13.86 Red fescue 2.7 17.76 LSD (.05) 10.42 4:4. 55 (A) II.1. Fig. 56 .oex .wsommm 60H mo Hmwma oaoauso Uwcflmwv HH03 may wuoz .onx m.oH um caonm mGOHuomm mmouo mama Amv odommm can c3maccmm cam Adv mmdhwmnan axosucox coaumSII.H.HH .mwh .mv .H.HH .mflm 57 11.2 I’m—(A) Eig. 58 .oovx .xdax Amv h.~ can Adv um c3onm mcofluowm mmouo mama mmmnmosan hxosucom coaumEII.N.HH .mfim Ame .~.HH .mflm mv 59 60 .oo¢x .NDHx Amv h.N UGM Adv mv um asonm mcowuowm mmouo mama osomom non c3macc0mll.m.HH .mHm Ame .m.HH .mflm g_.___._ - v 61 :3 4.5 .mE 62 .ooo.H~x .xsax Amv h.m 6:0 Amy me no ozonm mummHmouoHno mmmummsan wxooucmm coanoz mo mammnmouoflfi conaowaw c0flmmHEmGMHBII.v.HH .mfim Amy .¢.HH .mflm 15...»... ...I.L,. .I.......L|I.II IIIIII 63 64 .ooo.a~x .stx Ame h.~ can Amy m4 06 czoum mummadouoaao 050mmw own GSManmm mo mammumou0fl8 couuooaw cowmmfifimqmuall.m.HH .mHh Ame .m.HH .mflm POA PRATENSIS L. 'MERION' AND FESTUCA RUBRA L. 'PENNLAWN' AT REDUCED LIGHT INTENSITIES: III. PHOTOSYNTHETIC- RESPIRATORY RESPONSES ABSTRACT The objectives were to characterize the photosynthetic-respiratory responses of Kentucky blue- grass and red fescue to reduced light intensities. Merion Kentucky bluegrass and Pennlawn red fescue were grown in separate growth chambers at light intensities of 2.7, 10.8, and 43 klux. Light quality, soil moisture, and soil tem— perature were standardized among chambers. Infrared C02 analysis was used to measure assimilation rates, light saturation levels, and light compensation points of swards and individual plants. Both cultivars displayed decreased net photosyn- thesis (PN) and dark respiration (RD), lower light satura- tion levels, and decreased light compensation points under reduced light intensity. Swards generally had lower PN and RD rates, but higher light saturation levels and light compensation points than individual plants. Both cultivars responded similarly to reduced light intensity in terms of PN, light saturation levels, and 65 66 light compensation points. These factors could not be associated with the ability of Pennlawn red fescue to pro- vide a better turf than Merion Kentucky bluegrass in the shade. RD of individual plants of the red fescue was re- duced at the lowest light intensity, whereas the RD of the Kentucky bluegrass was not. This response may contribute to the positive C0 balance of the red fescue at reduced 2 light intensities, and thus to its shade adaptability. INTRODUCTION Kentucky bluegrass (Poa pratensis L.) and red fescue (Festuca rubra L.) will both provide a suitable turf in full sun, whereas red fescue generally will provide more desirable turf in shade (3, 21). Disease incidence (2) and tree root competition (19, 20) have been related to the loss of Kentucky bluegrass in shade. Reduced light intensity has a marked influence on plants by lowering the photosynthetic and respiratory rates, light compensation point, and light saturation level (1, 4, 5, 6, 8, 9, 10, ll, 12, 15, 16, 17, 23). Bohning and Burnside (10) were able to classify plants as 'sun' or 'shade' based on the higher light compensation point and light saturation level of the sun plants. Burn- side and Bohning (ll) later demonstrated the reversibility of this classification by placing sun plants in the shade and lowering the compensation point by up to l klux and saturation level by 10 klux. 67 68 The photosynthetic-respiratory balance is a crit- ical factor in shade adaptation. For a plant to survive, net photosynthesis must exceed respiration. This balance could be improved by lowering the respiration rate or light compensation point (8, 9, ll, 15). BjBrkman, Ludlow, and Morrow (8) showed the positive C02 balance of rain- forest species growing in dense shade was due to extremely low respiratory rates contributing to low light compensa- tion points. Bj6rkman et al. (9) studied the response of Atriplex patula L., a sun plant, to reduced light inten- sity. Low light intensity reduced the photosynthetic rate, light compensation point, light saturation level, and respiration rate. However, the plant could not tolerate light intensities as low as the rainforest species, ap- parently because it could not produce as efficient a photosynthetic apparatus. Shade tolerance may be related to photosynthetic efficiency in terms of carboxydismutase activity (6, 7, 8) or mesophyll resistance (14). Bj6rkman (6, 7, 8) corre- lated high light saturation levels with high carboxydis- mutase activity in sun plants. He concluded low carbo- xydismutase activity probably is a factor limiting the 69 capacity for light saturated photosynthesis in shade plants. Holmgren (14) explained light—saturated photo- synthetic rate differences in sun and shade plants based on mesophyll resistance. He attributed higher light- saturated photosynthetic rates in exposed clones of Solidago virgaurea to lower mesophyll resistance. Bj6rkman (4, 5) described the initial slope of the photosynthetic rate-light intensity curve as express- ing the capacity of photochemical processes. At light saturation, the photosynthetic rate is an expression of processes other than photochemical, e.g. carboxydismutase activity (6, 7, 8) and C0 diffusion rates (14). Bj6rkman 2 (4, 5) investigated the initial slope of the rate-intensity curves and light saturation levels of several species. Exposed clones had equal initial slopes regardless of pre- conditioning light intensity. Shaded clones had steeper slopes when grown at lower light. The light saturated photosynthetic rate was higher for the exposed ecotypes. He concluded the photosynthetic apparatus of the shaded ecotypes was able to use a low light intensity more effi- ciently, while the exposed ecotypes were able to use high light more efficiently. 7O Winstead and Ward (24) studied the physiological responses of warm season turfgrasses to shade. Tiflawn bermudagrass (Cynodon dactylon L. Pers.) displayed a de- crease in net photosynthesis and respiration at low light, whereas a small increase in net photosynthesis and a de- crease in respiration occurred in St. Augustinegrass (Stenotaphrum secundatum Walt. Kuntze.). St. Augustine- grass is the warm season counterpart of red fescue in re- gards to shade adaptation. The photosynthetic rate and light saturation level of turf are greatly influenced by shoot density, cutting height, and mowing frequency. Alexander and McCloud (1) investigated the light compensation point and light satur- ation level of individual leaves and swards of bermuda- grass. Isolated leaves had a light compensation point of 3.2 klux, and a light saturation of 32 klux. The light saturation level of swards cut at 5 cm and 20 cm was 75 and 54 klux, respectively. The differences were attri- buted to the orientation of leaves and the degree of interleaf shading. The objectives of this study were to investigate the net photosynthetic and dark respiratory responses of swards and individual plants of Merion Kentucky bluegrass 71 and Pennlawn red fescue under reduced light intensities. Light compensation points and saturation levels were also studied. It was anticipated this information may give further insight into the shade adaptive mechanisms of red fescue. Factors other than reduced light intensity af- fecting the growth of turf in shade (light quality, soil moisture, disease) were controlled or eliminated. METHODS AND MATERIALS Growth conditions were similar to those used in earlier studies (21, 22). 51252 A 14 hour photoperiod was used. Light intensities of 43, 10.7, and 2.7 klux (11.4, 5.0, and 1.4 x 103 uw cm- , respectively) were established in separate growth chambers. In an earlier study (21), both Merion Kentucky bluegrass and Pennlawn red fescue performed well at 43 klux. The Kentucky bluegrass turf quality was impaired at10.8 klux,whereas the red fescue continued to provide a suitable turf. Shoot and root growth of both cultivars was poor at 2.7 klux, however, the red fescue was able to provide a higher quality turf than the Kentucky bluegrass. Nominal differences existed among or within cham— bers in light quality (21). The light was rich in green and infrared wavelengths, weak in the blue and red re- gions (21). Pots were periodically rotated to compensate 72 73 for variation in light intensity within chambers. Separate growth chambers were used for each light inten- sity to avoid using shading materials that could seri- ously alter the turf microenvironment. Humidity A relative humidity of 70 t 5% was maintained in the growth chambers. Growing Medium All plants were grown in silica sand to reduce soil respiration during assimilation measurements. Plants were watered every other day with a complete Hoagland's (13) solution. Soil temperatures were maintained at 20 C during growth in the chambers. Plant Material Merion Kentucky bluegrass and Pennlawn red fescue were seeded in 10 cm diameter (12 cm depth) pots at 3 seeds/cmz, and germinated in the greenhouse. Plants were moved to the growth chambers when seedlings were 2 cm in height. All plants were grown at their respective light intensities for 6 weeks prior to assimilation measurements. 74 Plants were mown periodically at 5 cm. Occasional appli- cations of Karathané§>were required to control powdery mildew (Erysiphe graminis D.C.). C02 Exchange System A waterjacketed plexiglass assimilation chamber was constructed for use with the 10 cm pots (internal volume 3.3 liters). Tap water was circulated around the chamber for temperature control. 'Temperatures could be maintained at 23 i l C as indicated by a bulb thermometer inserted into the chamber. CO2 was introduced into the chamber above the plants, and was removed at the base of the chamber. The light source consisted of four 300 w reflector flood lamps. The light was passed through a water bath to reduce heat reaching the assimilation chamber. Figure 111.1 compares the spectral distribution within the assim- ilation chamber to that of the growth chambers. The C02 exchange system was closed, utilizing a FMI, Model RRP piston pump for air circulation. The flow rate was 600 ml/min. Copper tubing was used for all connections. Non-indicating Drierite provided a dessiccant. 75 A Beckman, Model 215 infrared gas analyzer, and a Sargent, Model SR 1 mv recorder were used. It was found that despite growing the plants in sand, soil respiration still interfered with assimilation measurements. All pots were flooded to 1 cm over the sand surface before C02 measurements to reduce soil respiration. Earlier studies (18) and preliminary work showed no sig- nificant influence of flooding on photosynthetic rates in the time necessary to complete measurements. Parameters Measured Measurements were made for both swards of turf and individual plants. One group of measurements were taken on the turf seeded at 3 seeds/cmz. A second series of pots were used which were thinned to 5 or 6 plants per pot to eliminate canopy effects of interleaf shading and C02 diffusion resistance. All assimilation rates were deter- mined between 330 and 270 ppm CO Rates were determined 2. 4 hours after the beginning of the growth chamber photo- period to minimize diurnal variation effects. Dark respiration rates were measured first, fol- lowed by net photosynthetic rates at light intensities of 1.35, 2.7, 5.4, 10.8, 21.5, 43, and 64.6 klux. Rates 76 were monitored for at least 10 minutes to obtain a straight line response at each light intensity. After all measurements were completed, shoots were removed and the flooded pot placed back in the chamber to determine soil respiration rate. Shoot dry weight and leaf area were determined as described earlier (20). Statistical Analysis Four replications were utilized. A completely randomized block analysis of variance was made on the two cultivars at each light intensity. The determined vari- ances at each light intensity were pooled, and a single LSD value (.05 level) was determined. RESULTS AND DISCUSSION Merion Kentucky bluegrass and Pennlawn red fescue displayed many of the typical physiological responses to reduced light intensity: reduced photosynthetic and respiratory rates, lower light saturation levels, and lower light compensation points (Tables 111.1, 111.2, and 111.3). Swards and individual plants generally re- sponded similarly, although the magnitude of the values was different. Swards had lower photosynthetic and respiratory rates, and higher light saturation levels and light compensation points than individual plants. Interleaf shading probably was the most important factor in reducing photosynthetic rates and increasing light saturation levels and light compensation points in the swards. Lower respiration rates in swards probably were due to C02 diffusion resistance within the canopy. 77’ 78 Photosynthetic Rates Net photosynthesis (PN) rates were measured at the preconditioning light intensity (Table 111.1) and at light saturation (Table 111.2). PN decreased as light intensity was reduced in both instances, for swards and individual plants. Larger reductions in P occurred between plants N grown at 43 and 10.8 klux when PN was measured at the pre- conditioning light intensity as opposed to measurement at light saturation. No differences were observed in the PN responses of the Kentucky bluegrass and the red fescue at reduced light intensities which would elucidate the shade adaptive mechanisms of red fescue. Anatomical work (22) revealed Merion Kentucky blue- grass chloroplasts to have significantly more grana than Pennlawn red fescue at reduced light intensities. 1n- creased grana development has been correlated to decreased carboxydismutase activity and C0 fixing ability (4, 5). 2 Pennlawn red fescue did not have the ability to fix more CO2 at reduced light intensities than Merion Kentucky bluegrass. The significance of this factor in relation to the shade adaptation of red fescue remains unknown. 79 Respiratory Rates Dark respiration (RD) rates after preconditioning to reduced light intensities are presented in Table 111.1. Swards and individual plants responded differently. RD of swards of both cultivars decreased with reduction in light intensity, although the decrease was not quite sig- nificant for red fescue. In contrast, RD rates of indi— vidual plants of the Kentucky bluegrass did not decrease under reduced light intensity. RD of individual plants of the red fescue was the same at 10.8 as at 43 klux, but was reduced approximately 50% at 2.7 klux. Reduced RD rates of swards under low light could be the result of canopy effects. The RD values probably represent the R of leaves at the top of the canopy only. D RD of lower leaves and sheaths may not be accounted for due to CO2 diffusion resistance through the canopy. A reduction in RD of individual plants of Pennlawn red fescue at low light intensities may be a shade adap- tive mechanism. Reduced RD would contribute to a positive C02 balance, despite the fact that PN was decreased under low light. An improved photosynthetic balance has been shown a factor in the shade adaptation of other species (8. 9, 11, 15). 80 Light Saturation Levels Saturation levels of both cultivars decreased under lower light (Table 111.3). Saturation of swards was not reached for either species at the highest light intensity used (64.6 klux). Alexander and McCloud (1) did report the light saturation level of bermudagrass swards cut at 5 cm occurred at 75 klux. Saturation levels of individual plants were slightly higher than those reported for individual leaves of most C3 plants. This could be due to the fact that the entire plant was used, and not a single leaf. Some inter- leaf shading, or perhaps the presence of older leaves and sheaths would raise the saturation level. No difference in the light saturation levels of swards or individual plants of Merion Kentucky bluegrass and Pennlawn red fescue was observed that could be related to shade tolerance. Light Compensation Points Light compensation points of both cultivars in swards decreased under lower light (Table 111.3). Com- pensation points were the same for individual plants at 10.8 and 43 klux, but were reduced for both cultivars at 81 2.7 klux. Compensation points found for individual plants are typical of those found for C plants. No difference 3 could be found in the compensation points of the Kentucky bluegrass and the red fescue at reduced light intensity. CONCLUSIONS The shade adaptation of several species has been related to an improved photosynthetic-respiratory balance (8, 9, ll, 15), reduced light compensation points (8, 9, ll, 15), and improved use of low light intensity as shown by an increased slope of the photosynthetic rate-light intensity curve (4, 5). The slope of the rate-intensity curve was similar for Merion Kentucky bluegrass and Penn- lawn red fescue at each light intensity, although the slope did decrease with lower light. The cultivars re- sponded similarly in terms of light compensation points (Table 111.3). Only the photosynthetic-respiratory bal- ance was observed in this study as a possible shade adap- tive mechanism of Pennlawn red fescue. The response of individual plants in Table 111.1 shows only the red fescue would have a positive C02 bal- ance at low light intensity over a 24 hour period. Merion Kentucky bluegrass at 10.8 and 2.7 klux displayed a nega- tive C02 balance. Despite this, the Kentucky bluegrass 82 83 was able to persist at these light intensities. Appar- ently the older leaves and sheaths of the Kentucky blue- grass were no longer photosynthetically active, and perhaps were acting primarily as a photosynthate sink. This contention is supported by earlier work (21), showing Merion Kentucky bluegrass leaf area was reduced much more than that of Pennlawn red fescue leaf area at reduced light intensities. Perhaps the older leaves of the Ken- tucky bluegrass senesce rapidly under low light, become a photosynthate sink, and are quickly sloughed off. REFERENCES Alexander, C. W., and D. E. McCloud. 1962. C02 up- take (net photosynthesis) as influenced by light intensity of isolated bermudagrass leaves con- trasted to that of swards under various clipping regimes. Crop Sci. 2:132-135. Beard, J. B. 1965. Factors in the adaptation of turfgrasses to shade. Agronomy J. 57:457-459. Beard, J. B. 1973. Turfgrass: Science and Culture. Prentice-Hall, Inc., Englewood Cliffs, N.J. pp. 181-209. Bj6rkman, 0., and P. Holmgren. 1963. Adaptability of the photosynthetic apparatus to light intensity in ecotypes from exposed and shaded habitats. Physiol. Plant. 16:889-914. Bjarkman, 0., and P. Holmgren. 1966. Photosynthetic adaptation to light intensity in plants native to shaded and exposed habitats. Physiol. Plant. 19:854-859. Bj6rkman, 0. 1968a. Carboxydismutase activity in shade-adapted and sun-adapted species of higher plants. Physiol. Plant. 21:1-10. Bj6rkman, 0. 1968b. Further studies on differentia- tion of photosynthetic properties in sun and shade ecotypes of Solidago virgaurea. Physiol. Plant. 21:84-99. Bj6rkman, 0., M. M. Ludlow, and P. A. Morrow. 1972. Photosynthetic performance of two rainforest species in their native habitat and analysis of their gas exchange. Ann. Rept. Dir., Dept. Plant Biol., Carnegie Inst., 1971-1972. pp. 94-102. 84 10. ll. 12. 13. 14. 15. 16. 17. 85 Bjorkman, 0., N. K. Boardman, J. M. Anderson, S. W. Thorne, D. J. Goodchild, and N. A. Pyliotis. 1972. Effect of light intensity during growth of Atriplex patula on the capacity of photosyn- thetic reactions, chloroplast components, and structure. Ann. Rept. Dir., Dept. Plant Biol., Carnegie Inst., 1971-1972, pp. 115-135. Bohning, R. H., and C. A. Burnside. 1956. The effect of light intensity on rate of apparent photosyn- thesis in leaves of sun and shade plants. Am. J. Bot. 43:557-561. Burnside, C. A., and R. H. Bohning. 1957. The effect of prolonged shading on the light saturation curves of apparent photosynthesis in sun plants. Plant Physiol. 32:61-63. Eagles, C. F., and K. J. Treharne. 1969. Photosyn- thetic activity of Dactylis glomerata L. in dif- ferent light regimes. Photosynthetica 3:29-38. Hoagland, C. R., and D. I. Arnon. 1950. The water culture method for growing plants without soil. Calif. Agr. Exp. Sta. Circ. 374., pp. 32. Holmgren, P. 1968. Leaf factors affecting light- saturated photosynthesis in ecotypes of Solidago virgaurea from exposed and shaded habitats. Physiol. Plant. 21:676-698. Loach, K. 1967. Shade tolerance in tree seedlings. 1. Net photosynthesis and respiration in plants raised under artificial shade. New Phytol. 66: 607-621. Schmidt, R. E., and R. E. Blaser. 1967. Effects of temperatures, light, and nitrogen on growth and metabolism of 'Cohansey' bentgrass (Agrostis palustris Huds.). Crop Sci. 7:447-451. Schmidt, R. E., and R. E. Blaser. 1969. Effect of temperature, light, and nitrogen on growth and metabolism of 'Tifgreen' bermudagrass (Cynodon dactylon spp.). Crop Sci. 9:5-9. 18. 19. 20. 21. 22. 23. 24. 86 Watschke, T. L., R. E. Schmidt, E. W. Carson, and R. E. Blaser. 1972. Some metabolic phenomena of Ken- tucky bluegrass under high temperature. Crop Sci. 12:87-90. Whitcomb, C. E. 1972. Influence of tree root compe- tition on growth response of cool-season turf- grasses. Agron. J. 64:355-359. Whitcomb, C. E., and E. C. Roberts. 1973. Competition between established tree roots and newly seeded Kentucky bluegrass. Agron. J. 65:126-129. Wilkinson, J. F.,and J. B. Beard. 1973. Poa pratensis L. 'Merion' and Festuca rubra L. 'Pennlawn' at re- duced light intensities: I. Morphological re- sponses. Proc. Sec. Intern'l Turfgrass Res. Conf., in press, and this volume. Wilkinson, J. Fu.and J. B. Beard. 1973. Poa pratensis L. 'Merion' and Festuca rubra L. 'Pennlawn' at reduced light intensities: II. Anatomical re- sponses. Crop Science, submitted, and this volume. Wilson, D., and J. P. Cooper. 1969. Effect of light intensity during growth on leaf anatomy and subse- quent light saturated photosynthesis among con- trasting Lolium genotypes. New Phytol. 68:1125- 1135. Winstead, C. W., and C. Y. Ward. 1973. Anatomical, morphological, and physiological studies relating to the persistance of southern turfgrasses when grown under reduced light intensity. Proc. Sec. Intern'l. Turfgrass Res. Conf. In press. 87 TABLE 111.1.--Net photosynthesis (PN) measured at three preconditioning light intensities and dark respiration (RD) of swards and individual plants of Merion Kentucky bluegrass and Penn- lawn red fescue grown at three light intensities. P Light N RD Species intensity (klux) Swards Individual Swards Individual (mg 002 dm'2 hr‘l) 43 4.92 13.30 1.61 4.55 KentUCky 10.8 1.08 1.85 0.61 4.30 bluegrass 2.7 0.42 1.49 0.21 4.11 43 3.70 11.76 1.25 2.94 R d 8 10.8 0.72 2.50 0.76 3.15 fescue 2.7 0.27 1.61 0.29 1.56 LSD (.05) 0.85 3.01 1.36 1.20 88 TABLE 111.2.--Light saturated net photosynthetic rates (PN) of swards and individual plants of Merion Kentucky bluegrass and Pennlawn red fescue grown at three light intensities. . . . P nght inten51ty N Swards (klux) Swards Individual (mg C02 dm"2 hr’l) 43 6.33 15.25 KentUCRY 10.8 3.93 11.00 bluegrass 2.7 2.73 11.03 43 4.78 13.11 Red 10.8 3.25 11.59 fescue 2.7 2.32 8.50 LSD (.05) 2.43 1.92 89 TABLE 111.3.--Light saturation levels and light compensation points of swards and individual plants of Merion Kentucky bluegrass and Pennlawn red fescue grown at three light intensities. , Light saturation Light compensation Light . . . , level p01nt Spec1es inten51ty (klux) . . . . Swards Ind1v1dual Swards Ind1v1dual (klux) 43 > 64 38 6 O 4.2 KentUCky 10.8 50 32 3.2 4.4 bluegrass 2.7 43 18 1.2 1.3 43 > 64 35 6.2 4.0 Red 10.8 47 32 3.5 4.2 fescue ' 2.7 43 19 1.35 1.5 LSD (.05) 9.2 9.4 2.1 1.8 .mumbfimno £u3onm on» can Hmnfimno cowumHHEHmmm onu CH cofluobflnumflc Hmuuommm on» no comflnmmfiooII.H.HHH .mHm ASE x 00b 00w 000 00¢ _ - _ a — — _ mwm2<10 IHBOKG II! 90 mmwmz