THE EFFECT OF CUTTING HEIGHT AND M'owING FREQUENCY, STAGE OF DEVELOPMENT, AND REDUCED ’ LIGHT INTENSITY 0N NET PHOTOSYNTHESIS, DARK RESPIRATION AND DISTRIBUTION 0F‘14C- ’ PHOTOSYNTHATE IN COOL SEASON TURFGRASSES. Dissertation for the Degree of Ph. D. ' MICHIGAN STATE UNIVERSHY JEFFREY V. KRANS 1975 Illii'illllllfllllllllllilliilflll 3 1293 01076 9804 This is to certify that the thesis entitled The effect of cutting height and mowing frequency, stage of devebopment, and reduced light intensity on net photosznthesis, dark respiration and dist- ribution of 1 C-photosynthate in cool season turf— grasses. presented by Jeffrey V. Krans has been accepted towards fulfillment of the requirements for Ph. D. .degree in Dept. of Crop and Soil Sciences m?\\‘> L—‘vweéi? Major professor Date Aug. 8, 1975 c-7539 / CC"? 1'" 2 1 W3 ABSTRACT THE EFFECT OF CUTTING HEIGHT AND MOWING FREQUENCY, STAGE OF DEVELOPMENT, AND REDUCED LIGHT INTENSITY ON NET PHOTOSYNTHESIS DARK RESPIRATION, AND DISTRIBUTION OF 14G-PHOTOSYNTHATE IN COOL SEASON TURFGRASSES By Jeffrey V. Krans Net photosynthesis, dark respiration, and distribution of 14C-photo— synthate were chosen as key parameters for determining a plant's overall physiological status. This study evaluated these physiological responses on turfgrass subjected to mowing stress, during seedling growth and develop- ment, and under reduced light intensity. It was anticipated that this information would aid in developing more effective cultural systems in turf management. In Merion Kentucky bluegrass (Poa pratensis L.), lower cutting heights and increased mowing frequencies resulted in reduced root production, decreased shoot growth, increased net photosynthesis, and increased dark respiration. Enhanced accumulation of 1l‘C—photosynthate in the root and stem fractions and lower incorporation of labelled photosynthate in the leaf fractions occurred as mowing frequencies increased. The trends in net photosynthate and distribution of 14C-photosynthate were attributed mainly to the relative location and proportions of assimilate supply and demand. The effect of mowing on accelerated dark respiration and defoliation of leaf area are suggested as the major contributing factors associated with Jeffrey V. Krans mowing stress. Proper mowing frequency (semi—weekly) and cutting height (6.25 cm) may eleviate mowing stress and improve turfgrass quality in Kentucky bluegrass. The effects of stage of development (1 to 10 weeks after seedling emergence at weekly intervals) on net photosynthesis, dark respiration and distribution of 14C—photosynthate were studied in Merion Kentucky bluegrass and Pennlawn red fescue (Festuca rubra L.). Lateral shoot development occurred after the fifth leaf stage in Kentucky bluegrass (3 to 4 weeks after seedling emergence) and after the third leaf stage in red fescue (3 weeks after seedling emergence). Tillering occurred in the axils of leaves below fully expanded leaves in both species. Tiller development preceded rhizome initiation in red fescue; whereas, tillers and rhizomes were not initiated preferentially to one another in Kentucky bluegrass. Enhanced photosynthesis, greater percent of leaf dry weight and raised dark respiration rates occurred during the initial weeks after seedling emergence (l to 2 weeks). The percent distribution of l4C-photosynthate shifted from the leaves to stems between the second and third weeks after seedling emergence in Kentucky bluegrass; whereas, this similar shift occurred between the third and fourth week after seedling emergence in red fescue. These developmental and physiological changes may signify critical changes in the developmental process. The effects of reduced light intensity on net photosynthesis, dark f ll‘C-photosynthate and relative respiration, root respiration, distribution 0 rate of 14C-photosynthate translocation were studied in six cool season turf- grass cultivars showing various degrees of shade tolerance. All the culti- vars responded similarly to reduced light intensities in terms of net photosynthesis, dark respiration, root respiration, and relative rate of Jeffrey V. Krans 14C-photosynthate translocation. Enhanced accumulation of 14C-photosynthate in the stem tissue in Nugget and A—34 Kentucky bluegrass occurred at the lowest light intensity. This response may be associated with a shade adaptive mechanism; however, further investigation is needed to elucidate this finding. THE EFFECT OF CUTTING HEIGHT AND MOWING FREQUENCY, STAGE OF DEVELOPMENT, AND REDUCED LIGHT INTENSITY ON NET PHOTOSYNTHESIS, DARK RESPIRATION AND DISTRIBUTION OF 14C-PHOTOSYNTHATE IN COOL SEASON TURFGRASSES. By ‘1'.“ _ («MI Jeffrey V? Krans 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 1975 To my wife, Kay ii ACKNOWLEDGEMENTS The author wishes to thank Dr. James B. Beard for his guidance and constructive criticism throughout my graduate program. The author also expresses appreciation to Dr. D. Penner, Dr. P. Rieke, Dr. K. T. Payne, and Dr. J. Vargas, for their assistance during my graduate program. iii TABLE OF CONTENTS LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . CHAPTER 1: THE EFFECT OF CUTTING HEIGHT AND MOWING FREQUENCY ON NET PHOTOSYNTHESIS, DARK RESPIRATION AND DIS- TRIBUTION OF 14C-PHOTOSYNTHATE IN MERION KENTUCKY BLUEGRASS Abstract . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . Materials and Methods . . . . . . . . . . . . . . . . . . . . Results and Discussion . . . . . . . . . . . . . . . . . . . Literature Cited 0 O I O O O O C O O O O O O O O O O O O 0 CHAPTER 2: THE EFFECT OF STAGE OF DEVELOPMENT ON NET PHOTO- SYNTHESIS, DARK RESPIRATION AND DISTRIBUTION OF 14C-PHOTOSYNTHATE IN MERION KENTUCKY BLUEGRASS AND PENNLAWN RED FESCUE Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . Materials and Methods . . . . . . . . . . . . . . . . . . . . Results and Discussion . . . . . . . . . . . . . . . . . . . Literature Cited . . . . . . . . . . . . . . . . . . . . . CHAPTER 3: THE EFFECT OF REDUCED LIGHT INTENSITY ON NET PHOTOSYNTHESIS, DARK RESPIRATION, AND DISTRI— BUTION OF 14C-PHOTOSYNTHATE IN COOL SEASON TURFGRASSES , Abstract 0 O O O O O O I O O O O O I O I O O I O O I O 0 iv Page vi viii 15 26 27 28 29 32 37 Introduction Materials and Methods . Results and Discussion Literature Cited CONCLUSIONS . . LIST OF REFERENCES Page 38 4O 43 46 58 6O LIST OF TABLES Table Page CHAPTER 1 1. The flux of photosynthetically effective radiation in the bands A=425-475 nm andjk=650-7OO nm from a 400 watt Sylvania mercury vapor lamp (H 33) . . . . . . . . . . . . . . . . . . . l7 2. The effect of mowing height and frequency on the distribution of dry weightixiroots, stems, leaves, and rhizomes (rhiz) in Merion Kentucky bluegrass at 2, 4, and 6 weeks after treatment initiation . . . . . . . . . . . . . . . . . . . . . l8 3. The effect of mowing height and frequency on net C02 fixation capacity at 2, 4, and 6 weeks after clipping treatment initiation . . . . . . . . . . . . . . . . . . . . . . . . . . l9 4. The effect of mowing height and frequency on the number of lateral shoots in Merion Kentucky bluegrass at 2, 4, and 6 weeks after treatment initiation . . . . . . . . . . . . . . . 20 5. The effect of mowing height and frequency on the net regrowth after mowing Merion Kentucky bluegrass at 2, 4, and 6 weeks after treatment . . . . . . . . . . . . . . . . . . . . . . . . 21 6. The effect of mowing height and frequency on net photosynthesis (Pu) and dark respiration (RD) in Merion Kentucky bluegrass at 2, 4, and 6 weeks after treatment initiation . . . . . . . . 22 7. The effect of mowing height and frequency on the percent distribution of dry weight in roots, stems, leaves, and rhizomes (rhiz) in Merion Kentucky bluegrass at 2, 4, and 6 weeks after treatment initiation . . . . . . . . . . . . . . 23 8. The effects of mowing height and frequency on the percent distribution of ll‘C-photosynthate in the roots, stems, leaves, and rhizomes (rhiz) in Merion Kentucky bluegrass at 2, 4, and 6 weeks after treatment initiation . . . . . . . . 24 CHAPTER 2 l. The effect of stage of development on the percent distribution of dry weight in Merion Kentucky bluegrass and Pennlawn red fescue . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 vi Table 2. The effect of stage of development on the net photosynthe- sis (PN) and dark respiration (RD) in Merion Kentucky bluegrass and Pennlawn red fescue . . . . . . . . . . . . . . The effect of stage of development on the percent distribu- tion of 14C-photosynthate in Merion Kentucky bluegrass and Pennlawn red fescue . . . . . . . . . . . . . . . . . . . . CHAPTER 3 The effect of three light intensities on the distribution of dry weight in the roots, stems, leaves, and rhizomes in six cool season turfgrasses after 8 weeks of growth at preconditioning light intensities . . . . . . . . . . . . . The effect of three light intensities on the percent distri- bution of dry weight in the roots, stems, leaves, and rhi- zomes in six cool season turfgrasses after 8 weeks of growth at preconditioning light intensities . . . . . . . . . . . The effect of three light intensities on the percent distri- bution of l C-photosynthate in the roots, stems, leaves, and rhizomes in six cool season turfgrasses after 8 weeks of growth at preconditioning light intensities . . . . . . . . The effect of three light intensities on the relative rate of C-photosynthate transport measured at k and 2 hrs after labelling in the upper roots, lower roots, stems, and leaves in six cool season turfgrasses after 8 weeks of growth at preconditioning light intensities . . . . . . . . . . . . . . The effect of three light intensities on the net photosynthe- tic and dark respiration rates in six cool season turfgrasses after 8 weeks of growth at preconditioning light intensities. The effect of three light intensities on root respiration rates measured by two methods in six cool season turfgrasses after 8 weeks of growth at preconditioning light intensities. . . . vii Page 35 36 49 50 51 52 53 54 Figure LIST OF FIGURES CHAPTER 1 l. The effect of mowing (2.5 cm cutting height) on dark res- piration monitored over a 72 hr period in Merion Kentucky bluegrass . . . . . . . . . . . . . . . . . . . . . . . . . . CHAPTER 3 1. The relative rate of 14C—assimilate translocation. (A) Plants, from left to right - Merion Kentucky bluegrass, Merion Kentucky bluegrass, Park Kentucky bluegrass, Park Kentucky bluegrass. (B) Radioautographs, from left to right - Merion Kentucky bluegrass % hr after labelling, Merion Kentucky bluegrass 2 hr after labelling, Park Kentucky bluegrass % hr after labelling, and Park Kentucky bluegrass 2 hr after labelling . . . . . . . . . . . . . . . . . . . . . . . . . 2. The relative rate of 14C-assimilate translocation. (A) Plants, from left to right - Nugget Kentucky bluegrass, Nugget Ken- tucky bluegrass, A—34 Kentucky bluegrass, Ar34 Kentucky blue~ grass. (B) Radioautographs, from left to right — Nugget Kentucky bluegrass % hr after labelling, Nugget Kentucky bluegrass 2 hr after labelling, A-34 Kentucky bluegrass k hr after labelling, and A-34 Kentucky bluegrass 2 hr after labelling . . . . . . . . . . . . . . . . . . . . . . . . 3. The relative rate of 14C-assimilate translocation. (A) Plants, from left to right - Pennlawn red fescue, Pennlawn red fescue, Wintergreen chewings fescue, Wintergreen chewings fescue. (B) Radioautographs, from left to right - Pennlawn red fescue % hr after labelling, Pennlawn red fescue 2 hr after label- ling, Wintergreen chewings fescue % hr after labelling, and Wintergreen chewings fescue 2 hr after labelling . . . . . viii Page 25 55 56 57 INTRODUCTION Net photosynthesis, dark respiration, and the distribution of photo- synthate are key parameters in describing a plant's physiological status. Net photosynthetic measurements are determined by monitoring the incorpora- tion of C02 into a plant system. Dark respiration measurements are deter- mined by monitoring the evolution of C02 from plant leaves. The major por- tion of C02 given off by the plant results from decarboxylation reactions in the tricarboxylic acid cycle. These reactions result in reduced pyri- dine nucleotide (NADH and NADPH) formation which are oxidized via the electron transport chain in mitrochondria to form the high energy ATP molecules. This measurement of dark respiration provides an estimation of the relative rate of energy use. Combining the rate of dark respiration with the total leaf area will provide an indication of the total energy requirements in the plant leaves. Both the photosynthetic and dark respira— tion measurements have been used extensively in the plant science as indi- cators of metabolic activity. The distribution pattern of photosynthate is directed by the relative location of assimilate demands within the plant (19). This pattern of distribution usually indicates areas of high meta- bolic activity associated with growth and/or assimilate storage. Moni~ toring these shifts in metabolic activity in the plant system is an impor- tant aspect of plant physiology. The objectives of this investigation were to monitor net photosynthesis, dark respiration and distribution of 14C-photosynthate during mowing stress, developmental growth changes, and reduced light intensities in cool season 1 turfgrasses. These treatments were selected as being important management and environmental factors associated with turfgrass culture. Mowing is the most widely used cultural practice common to all turfgrass species. Growth and morphological responses in turfgrass have been exten- sively investigated under mowing stress (8, 21, 22, 33). This research was designed to investigate the physiological responses of mowing stress. It is anticipated that this study will lead to more effective mowing prac- tices. Merion Kentucky bluegrass (Poa pratensis L.) was selected for use in this study because of its wide dominant planting in the temperate climates. DevelOpmental changes associated with turfgrass seedling growth are important aspects of turfgrass culture. Rapid, successful turfgrass esta- blishment is required for effective dust and erosion control. Investiga- tion of the physiological and morphological reSponses associated with seed— ling establishment may indicate critical periods requiring intensified cultural management. Knowledge of these physiological changes may provide a greater understanding of turfgrass growth and development and lead to more effective establishment practices. Merion Kentucky bluegrass and Pennlawn red fescue (Festuca rubra L.) were selected for use in this study. Both species are widely grown in the temperate climates. Considerable difficulty can be experienced in the culture of turfgrass under shaded conditions. Various components of the microenvironment are adversely altered under shade. An obvious and detrimental effect of shade is reduced light intensity. Red fescue has been reported as a dominant shade tolerant cool season turfgrass (8). Past investigations have shown poor shade tolerance in Kentucky bluegrass (58, 59). Recently, two cultivars of Kentucky bluegrass (Nugget and A-34) have shown excellent shade tolerance. This investigation of the physiological responses associated with shade tolerant and intolerant cultivars of Kentucky bluegrass and fescue species may elucidate possible shade adaptive mechanisms. Know— ledge of these shade adaptations may be helpful in selection of additional turfgrass varieties for use in the shade. The research presented in this investigation was divided into three separate studies. Each study will be handled as an individual research project and will be discussed accordingly. The three areas of investiga- tion included the effects of a) mowing stress, b) develOpmental changes, and c) reduced light intensity on net photosynthesis, dark respiration, and distribution of 14C-photosynthate in cool season turfgrass species. CHAPTER 1 THE EFFECT OF CUTTING HEIGHT AND MOWING FREQUENCY ON NET PHOTOSYNTHESIS, DARK RESPIRATION, AND DISTRIBUTION OF 14C-PHOTOSYNTHATE IN MERION KENTUCKY BLUEGRASS (POA PRATENSIS L.) Abstract This study evaluated the effects of cutting height (2.5 cm, 6.25 cm, and not mowed) and mowing frequency (semi-weekly, weekly, and biweekly) on net photosynthesis, dark respiration, and distribution of 14C-photosynthate in Merion Kentucky bluegrass (Poa pratensis L.). Root production declined, shoot growth decreased, net photosynthesis increased and dark respiration rates increased as mowing frequency increased and cutting heights decreased. The percent of 1[IF-photosynthate incorporation in the root and stem frac- tions increased as mowing frequency increased only. The trends in photo- synthesis and percent distribution of 14C-photosynthate followed the rela- tive changes in assimilate supply and demand as created by the degree of leaf defoliation. The results did not reflect on the growth responses asso- ciated with mowing stress. The effect of accelerated dark respiration and severe defoliation of leaf area are suggested as the major contributing factors associated with mowing stress. Proper mowing frequency (>semi-weekly) and cutting height (6.25 cm) may help eleviate mowing stress and improve turfgrass quality in Kentucky bluegrass. Introduction Mowing is the most widely used cultural practice common to all turf— grass species. The grasses used in turfs evolved under the selective graz- ing pressures of animals. They adapted by developing a stem apex located near the soil and a basal type leaf growth (2). This evolutionary develop- ment does not indicate mowing is advantageous. Actually, it is detrimental due to the removal of photosynthetically active leaf tissue and frequent wounding. The loss of leaf area has been generally accepted as the major cause of mowing stress in turfs (2, 12). Wounding has been shown to sig- nificantly increase respiration in dicotyledons (9, 10, 18). However, this response has not been reported as a contributing factor relating to mowing stress. The rise in respiratory activity associated with wounded plant tissue gradually increases to a maximum within one to two days and declines thereafter to the levels originally observed before injury (19). This accelerated respiration has been prevented by actinomycin D and puromycin applications and appears to be dependent on RNA and protein synthesis (1, 22). Numerous investigators have reported on the effects of mowing stress on various physiological, morphological, and developmental responses of turfgrasses. As mowing height is moderately lowered and mowing frequency increased, turfgrass plants exhibit reduced carbohydrate synthesis and Stuarage (5, 6, 17); increased shoot density (ll, 14, 15); decreased leaf vdmith (12, 21); increased succulence (14); and decreased root production (7, 14, 15). The photosynthetic-respiratory balance can be an important factor in Plarrt survival and recuperation from stress. Madison (12) suggested that PhOtKDsynthesis may be reduced during mowing stress. However, net photosynthetic and dark respiration rates have not been reported under mowing stress differential. Photosynthate distribution patterns usually indicate sites of major metabolic activity. The pattern of distribution during mowing stress may provide a better understanding of the mechanism causing severe root reduction. In this investigation, net photosynthesis, dark respiration, and distribution of 14 C-photosynthate were measured to determine the effects of cutting height and mowing frequency as mowing stress factors on turf- grass growth. In addition, the major associated morphological and growth responses were monitored. Materials and Methods Treatments included three cutting heights (2.5 cm, 6.25 cm, and not mowed) and three mowing frequencies (semi-weekly, weekly, and bi-weekly). Mowing frequencies were applied in a factorial design on the 2.5 and 6.25 cm mowing heights. Individual plants of Merion Kentucky bluegrass (Pg§_ pratensis L.) were grown from seed in 5 cm diameter by 15 cm deep plastic containers filled with washed silica sand. A nutrient solution drench (8) was applied every third day and plants were irrigated with tap water on alternate days. Containers were perforated to allow free drainage. Plants were grown in an environmental growth chamber at 23 C day and 16 C night temperatures. The light radiation was 1000 DE M52 sec"1. The rela- tive humidity was 70 i 5% and the photoperiod was 14 hours. Plants were grown for 8 weeks prior to initiation of mowing treatments. This time period allowed the plants to reach a suitable level of maturity. All newly initiated tillers and rhizomes were removed at the crown surface during this initial growth period. This was done to facilitate evaluation of the effects of mowing stress on tiller and rhizome development from a single crown. Once mowing treatments were initiated, the clippings were collected from all treatments, frozen, and freeze dried. Photosynthesis, dark respiration, distribution of 14C-photosynthate, and number of lateral shoots were measured at 2, 4, and 6 week intervals after mowing treatments were applied. These time intervals between measure— ments were selected to monitor the initial and prolonged effects of mowing stress. Photosynthetic and dark respiration rates were measured by moni— toring the rate of change in C02 concentration between 270 and 330 ppm in a closed C02 exchange system. This system consisted of a Beckman Model 215 infrared gas analyzer, a FMI Model RRP piston pump for air circulation, a Sargent Model SR strip chart recorder, a Drierite column, and a cyclindrical assimilation chamber (internal volume 0.22 liters). The flow rate was 500 ml/min and total volume of the system was 0.313 liters. The connecting lines were constructed primarily of 0.63 cm diameter copper tubing with short lengths of tygon tubing to aid in flexibility. A 400 watt Sylvania mercury vapor lamp (Table l) was placed above the assimilation chamber. The light was passed through a water bath to reduce heat reaching the assimilation chamber. A radiation level of 850 DE M"2 sec'l-was maintained at the plant surface. The entire system was located in a Puffer Hubbard UNI—THERM refrigerator for constant temperature (23 1'1 C). A bulb thermometer was inserted into the chamber for monitoring temperature. Soil respiration was eliminated by flooding the container with distilled water to a depth of 0.5 to 1.0 cm above the sand surface. Photosynthetic and dark respiration rates were measured 4 hours after initiation of the light period. Dark respiration was monitored first, followed by photosynthetic measurements. Plants were treated with l uCi of 14C02 for the purpose of measuring photosynthate distribution. Labelling was done by diverting the air stream within the C02 exchange system into a reaction flask containing 0.2 ml (1 uCi) of Na14CO3 solution (Nal4CO3 in H20) reaction with 5 ml of 45% lactic acid. The 14C02 evolved was continually circulated around the grass leaves for 30 min during which time the plant reached its C02 compensation concentration. The plants were returned to the environmental growth chambers after labelling for a 24 hr period and were then harvested by washing the root system free of sand, immediately frozen, and stored. Plants were subsequently sectioned into leaf, root, stem, and rhizome fractions and freeze dried. The leaf fraction consisted of leaf tissue located above the collar. The crown and leaf sheath were included in the stem fraction. Root segments were removed below and immediately adjacent to the crown. The rhizome fraction consisted of subsurface secondary lateral shoots that developed extravaginally and extended horizontally. Only those rhizomes which did not reach the soil surface were included in this fraction. Rhizomes which had emerged into the light and formed photosynthetically active leaves were separated into leaf and stem fractions. Each plant segment was weighed and a sub—sample (50 to 100 mg) taken for a determination of the amount of 14002 incorporation. The amount of radio— activity was measured by combusting plant samples in a sealed 1000 m1 Erlenmeyer flask containing an oxygen pure atmosphere. The radioactive 1[‘COZ which evolved was captured in 20 ml of ethanol-ethanolamine (2:1). A 5 ml aliquot was combined with 10 ml of scintillation solution [0.3 g of dimethyl POPOP (1,4-bis 2-(4-methyl-S-phenyloxazolyl)-benzene, 5.0 g of PPO (2,5-diphenyloxazole) per liter of toluene] and radioassayed by liquid scintillation spectrometry. Counting efficiency was determined by channel ratios and ranged between 70 to 75%. Net radioactive incorpora- tion was measured in disintegrations per minute (dpm). Leaf area was determined with a LI-COR, Model LI-3000 portable area meter using a sub-sample of fresh leaf blades (5 to 10). Leaf area was measured at each treatment and sampling period. A leaf areazweight ratio was used to estimate the total leaf area. Each mowing treatment was replicated three times in a completely ran- domized block design. Differences between treatment means were tested statistically using Duncan's Multiple Range Test. Orthogonal comparisons were used to statistically evaluate the main effects of mowing height and frequency. Results and Discussion The net distribution of dry weight in the root, stem, leaf, and rhi- zome fractions decreased under lower cutting heights and increased mowing frequencies (Table 2). This decrease in dry weight measured in the leaf and stem fraction is an obvious reflection of the degree of defoliation. The decline in root mass associated with the lower cutting heights and increased mowing frequencies is a well documented effect of mowing stress (7, 14, 15). Lower cutting heights and increased mowing frequencies resulted in reduced net C02 fixation capacity (Table 3). This relationship is mainly associated with the loss of photosynthetically active leaf area (Table 2). Reduced leaf area during mowing is generally accepted as the major cause of de- creased root production (2, 12). No differences in net C02 fixation capa- city were measured at 6 weeks after treatment initiation (6.25 cm cutting 10 height) as mowing frequency decreased. This trend was associated with abnormally low photosynthetic measurements resulting from excessive interleaf shading (Table 6). Shoot density, as measured by the total number of primary and secon- dary lateral shoots, was greater at the 6.25 cm cutting height than the 2.5 cm or not mowed treatments (Table 4). These findings agree with reports showing stimulation of shoot density under moderate defoliation (ll, 14, 15). The 2.5 cm cutting height is excessively low for Kentucky bluegrass (2) and may have inhibited shoot initiation. Vaartnou (25) showed similar restrictions in lateral shoot development in Agrostis L. when mowed ex- cessively low. Shoot density increased at the 6.25 cm and 2.5 cm height as mowing frequency decreased at 2 and 4 weeks after treatment initiation (Table 4). However, at 6 weeks after treatment initiation, no differences were measured and a reversed numerical trend was indicated at the 6.25 cm cutting height. Madison (13) reported greater shoot density at moderate cutting heights as mowing frequency was increased in creeping bentgrass (Agrostis_palustris Huds.) Net growth after mowing increased under higher mowing heights and decreased mowing frequencies (Table 5). Similar trends in the regrowth rate following defoliation have been reported for grasses mowed at moderate heights and frequencies (11, 12, l3, 14). Madison (12) suggested that the regrowth after mowing is reduced on frequently mowed turf because of a decline in photosynthesis and attendent loss of leaf surface. Net photosynthetic rates tended to increase as cutting heights were lowered and mowing frequencies increased (Table 6). Statistical comparisons of cutting heights pooled across mowing frequencies revealed significantly higher net photosynthetic rates in the order of 2.5 cm > 6.25 cm > not mowed for all sampling periods. 11 A statistical comparison of mowing frequency on net photosynthesis resulted in the semi-weekly frequency being significantly greater than the biweekly treatment both at the 2.5 cm and 6.25 cm cutting heights. High photosynthetic rates measured at 2 and 4 (2.5 cm cutting height; semi-weekly and weekly frequencies) after treatment initiation are inter- preted in terms of supply and demand for photosynthate. Reduced cutting heights and increased mowing frequencies resulted in greater proportion of sink (roots plus stems) to source (leaves) (Table 7). This relationship caused by defoliation resulted in greater assimilate demand on the photo- synthetically active leaf area. Vanden Driessche (26) and Maggs (16) re- ported greater photosynthetic rates after partial defoliation of leaves of dicotyledons. Both attributed this response to increased assimilate demand on the remaining photosynthetic area. Thorne (23) increased net assimila- tion in sugar beets (Beta vulgaris) by grafting larger roots to similar tops. This increase in assimilation was interpreted as a high assimilate demand on the existing leaves. The above results (16, 23, 26) and the find- ings of this study suggest a "feedback" mechanism in which the demand for photosynthates regulates the rate of photosynthesis. Lower photosynthetic rates were measured at 4 and 6 weeks after treatment initiation in grass mowed at 2.5 cm (biweekly frequency), 6.25 cm (weekly and biweekly frequencies) and not mowed treatments (Table 6). These trends in photosynthesis are attributed in part to excessive interleaf shading. Enhanced rhizome development at the higher cutting heights and reduced frequencies indicate greater assimilate demand in these treatments. This trend may indicate higher photosynthetic measurements based on effect of 12 assimilate demand. However, this effect was not observed and may have been negated by excessive interleaf shading. Photosynthetic rates appeared to decline from the second through sixth week following treatment initiations. This trend is attributed to greater interleaf shading and reduced sink to source ratios, as shoot density increased. Dark respiration rates were higher in grass mowed at the semi-weekly frequency both at the 2.5 cm and the 6.25 cm cutting heights for all sampling periods (Table 6). This trend in respiration is associated in part to a wounding and accelerated growth response (Figure 1). Dark res- piration was periodically monitored for 72 hours after mowing. Respiration rates increased more than twofold following cutting. Dark respiration reached a maximum 20 hours after cutting, declined slightly and leveled off to values noticeably greater than that measured before cutting. The initial rise in respiration (O to 2 hrs) is attributed mainly to wound respiration. The continued rise and elevated rates thereafter may be re- lated to enhanced lateral shoot initiation caused by defoliation. This effect of mowing turfs has not been reported previously and may be an important factor contributing to mowing stress. A trend in reduced dark respiration rates were measured from the second to fourth sampling periods in all treatments (Table 6). This relationship may indicate an adjustment by plants to frequent wounding. The methods used in severing the turf during mowing may influence wound respiration. A tearing or ripping of the leaf tissue (rotary mowers) may increase the wound response compared to a clean cutting action (reel mowers). This aspect of mowing requires further investigation and may be an important factor associated with cutting methods. 13 The relative location of assimilate demands in plant systems are attributed as the major driving force in photosynthate distribution (4). High accumulation of ll‘C-photosynthate was measured in the root and stem fractions in plants mOwed at increased frequencies (Table 8). This trend corresponded with enhanced movement of labelled photosynthate out of the leaves. An exception was at 4 weeks after treatment initiation where the stem fraction showed no significant differences among mowing frequencies. A statistical comparison of cutting heights revealed few differences in the percent distribution of 14C-photosynthate within the root, stem and leaf fractions. Increased cutting frequencies resulted in a greater propor- tion of sink (root plus stem) to source (leaves) two weeks after treatment initiation (Table 7). This relationship caused by defoliation resulted in greater assimilate demand on the photosynthetically active leaf area. High percent incorporation of 14C-photosynthate in the root and stem fraction and increased movement of labelled photosynthate out of the leaves is attributed in part to the direct effects of defoliation. The distribution pattern of labelled photosynthate at 4 and 6 weeks after treatment initiation may be related to different rhizome development (Table 7). Increased rhizome development occurred under higher cutting heights and decreased mowing frequency. This trend results in increased assimilate demand on the leaf fraction. This relationship is suggested as the major driving force resulting in enhanced percent of 14C-photosynthate movement out of the leaves. The reduction in the percent of incorporation of labelled photosynthate in the root fraction may be related to the greater sink capacity associated with rhizome development. The relationship of relative sink capacity between roots and rhizomes may indicate rhizome development occurs at the expense of root production (Table 8). 14 The pattern of 14C-photosynthate distribution and high photosynthetic rates do not accurately reflect on the reduction in total root mass or decline in turfgrass vigor associated with excessively low cutting heights and frequent mowing. The effect of accelerated dark respiration and severe defoliation of leaf area are suggested as the major contributing factors associated with mowing stress. Proper mowing frequency (>semi- weekly) and cutting height (6.25 cm) may help alleviate mowing stress and improve turfgrass quality in Kentucky bluegrass. 10. ll. 12. 13. 15 Literature Cited Asahi, T., Y. Honda, and I. Uritani. 1966. Increase of mitochondrial content in sweet potato after wounding. Arch. Biochem. Biophys. 113:498-99. Beard, J. B. 1973. Turfgrass: Science and Culture. Prentice-Hall, Inc., Englewood Cliffs, N.J. pp. 230-257. Brown, M. E. 1943. Seasonal variations in the growth and chemical com- position of Kentucky bluegrass. Missouri Ag. Experiment Station, Research Bulletin No. 360 pp. 5-56. Crafts, A. S. anui C. E. Crisp. 1971. Phloem transport in plants. W. H. Freeman and Co., San Francisco, Calif. pp. 125-156. Dodd, J. D., and H. H. Hopkins. 1958. Yield and carbohydrate of blue grama grass as affected by clipping. Transactions of Kansas Academy of Science. 61:(3):280-287. Everson, A. C. 1966. Effects of frequent clipping at different stubble heights on western wheatgrass (Agropyron smithii Rybd.). Agron. J. 58:(1):33—35. Harrison, C. M. 1931. Effect of cutting and fertilizer application on grass development. Plant Physiol. 6:669-684. Hoagland, D. R. anui D. I. Arnon. 1950. The water culture method for growing plants without soil. Calif. Agr. Exp. Sta. Circ. 347. p. 32. Hulme, A. C., M. J. C. Rhodes, T. Galliar and L. S. C. Wooltorton. 1968. Metabolic changes in excised fruit. IV. Changes occurring in discs of apple peel during the development of the respiration climacteric. Plant Physiol. 43:1154-61. Imaslki, J. M., A. Uchigamo, and J. Uritani. 1968. Effect of ethylene on the inductive increase in metabolic activities in sliced sweet potato roots. Agr. Biol. Chem. 37:387-89. Madison, J. H. 1960. The mowing of turfgrass. I. The effect of season, interval, and height of mowing on the growth of Seaside bentgrass turf. Agron. J. 52:449-456. Madison, J. H. 1962. The mowing of turfgrass. II. Response of three species of grass. Agron. J. 54:250-252. Madison, J. H. 1962. Mowing of turfgrasses. III. The effect of rest on Seaside bentgrass turf mowed daily. Agron. J. 54:252-253. 14. 15. l6. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 16 Madison, J. H. 1962. Turfgrass ecology. Effects of mowing, irrigation, and nitrogen treatments of Agrostis palustris Huds., "Seaside" and Agrostis tenuis Sibth., "Highland" on population, yield, rooting, and cover. Agron. J. 54:407—412. Madison, J. H. and R. M. Hagan. 1962. Extraction of soil moisture by Merion bluegrass (Poa pratensis L. 'Merion') turf, as affected by irrigation frequency, mowing height, and other cultural operations. Agron. J. 54:157-160. Maggs, D. H. 1963. The reduction in growth of apple trees brought about by fruiting. J. Hort. Sci. 38:119—122. McCarty, E. C. and R. Price. 1942. Growth and carbohydrate content of important mountain forage plants in central Utah affected by clipping and grazing. U.S.D.A. Tech. Bulletin No. 818. pp. 1-51. McGlasson, W. B. and H. K. Pratt. 1964. Effects of wounding on res- piration and ethylene production of cantaloupe fruit tissue. Plant Physiol. 39:128-132. Meyer, 8. B., D. B. Anderson, R. H. Bohning, and D. G. Fratianne. 1973. Introduction to Plant Physiology. D. Van Nostrand Co., New York, New York. pp. 235. Mitchell, K. J. 1955. Growth of pasture species. 11. Perennial ryegrass (Lolium perenne), cocksfoot (Dactylis glomerata), and paspalum (Paspalum dilatatum). New Zealand J. Sci. & Tech. Sec. A. 37(1):8—26. Mitchell, K. J. and S. T. J. Coles. 1955. Effects of defoliation and shading on short-rotation ryegrass. New Zealand J. Sci. & Tech. Sec. A. 36(6):586-604. Sakano, K. and T. Asahi. 1971. Biochemical studies on biogenesis of mitochondria in wounded sweet potato root tissue. I. Time course analysis of increase in mitochondrial enzymes. Plant and Cell Physiology. 12:417-426. Thorne, J. H. and R. Koller. 1974. Influence of assimilate de- mand on photosynthesis, diffusive resistances, translocations and carbohydrate levels of soybean leaves. Plant Physiol. 54:201-207. Wilkinson, J. F., J. B. Beard and J. V. Krans. 1975. Photosynthe— tic respiratory responses of 'Merion' Kentucky bluegrass and 'Pennlawn' red fescue at reduced light intensities. Crop Sci. 15:165-168. ' Vaartnou, H. 1967. Responses of five genotypes of Agrostis L. to variations in environment. Ph.D. Thesis. Oregon State Univer- sity. pp. 1-149. Vanden Driessche, R. and P. F. Wareing. 1966. Dry-matter pro- duction and photosynthesis in pine seedling. Ann. Bot. 30:673—682. 17 Table l. The flux of photosynthetically effective radiation in the bands A = 425-475 nm and A = 650—700 nm from a 400 watt Sylvania mercury vapor lamp (H 33). Band Flux of radiation . —2 nm micro watts cm 425-475 1221 650-700 2376 18 .umoH omamm oamwuasz m.amoa=a mam he Hm>oH Nm Gnu um ucwuommav haucmoawacmwm uoc mum mumuuma canoo saga mmanaoo canuwa mcmoz« 0mm emmm comma mama uma mama mmaa mama an mam ans an“ eases HOG Sam eoom umsa uwsa Dom mama amaa omaa am was ems emm N Ema oasa umNN eaoa no maaa saw was «No seam uaam sea a 2mm omaa onsaa seam mo Sow Doe uma so emm can uaam ~\a m~.o Dom Seam pawa smom am new use cos we uaa cam pen a we saw mmm Asa so see Ema cam we now seem «mm a GM mam wok «so no mom mom mam Ho oa mam Ema ~\a m.~ IIII II IIIIIIIIIIIIIIIIII waI IIII I 3x33 33 Nazm mm>moq mEoum muoom Nfism wm>mma mEOum muoom Nfism mo>mmA mEoum wuoom hocoadmuw unwwon wcaaoz wafiuuso mxwo3 o mxowa c mxooa N «unwama ham «0 cowusnauumaa .aowumauwcw ucme lummuu umuwm mxom3 o mam .q .N um mmmuumsan >xusucwm coaumz Ca Ananuv mmEoufinu mam mo>moa .mEmum .muoou ca unwamz zap mo coauanauumaw Gnu co zucosvouw mam uLme; wcfi3oa mo uoommo one .N manna 19 .umoH mwcmm maawuaaz m.amu==n DAu an Ho>mH Nm Gnu um uaouomwaw maucmoamaamfim uoc mum mumuuoa aoaaoo nuaa maadaoo aHSuHB mammz« a NoHN o oqu v mama pesos mom a quN o mmmN v mea N n moaN n Nme n HMN H n HwHN n mama n mmn N\H mN.o a «mma n mmqa o oNoa N n mmca no omoa n awe H m ama m mmo m Non N\H m.N IIIIIIIIIIIIIIIIII HIE NoowEI II A333 33 wxmoa o mxoms e mxmm3 N xoaozvmuw unwfio: wmwzoz mcfiuuso Reoaumxaa N8 umz .cowumauficw uaoEumouu wcqaawau noumm wxooa 0 Cam .c .N um zuwomamo coaumxau Nov um: onu so zomesvouw mam unmwon mafiaoe mo uoowwm mnH .m Danae 20 .umoe owcmm DHQHuHsz m.amo::n msu an Ho>oH Nm ecu um ucmummeu mHucmonchHm uo: mum muouumH coaaoo nuHB maazHoo cHnuHa mammz« m NN a HH 6 OH @0368 ac: am mm o ma so a N am 0N n NH on N H n mm a HH m e N\H mN.o mm wN 3 NH mu m N m NN am a pm m H m «N m N mm m N\H m.N Amxmm3v Aaov mxmoa o wxmoa q mxooz N zocmnuoum uanos waaaoz weaauau uamHn\«muoo£m Hmumumg .aoHumHuHaH uaoaumouu woumo meD3 9 was .q .N um mmmquSHn axoauaox :oHuoz aH muooam HmumumH No wonabc osu co >ocmsvoum mam uanmn wcHsoa mo uoommo 0:9 .c mHan 21 .vaHumo mcHHnamm cooaumn mHm>umuaH Hows cam now nuBouw scum uswwma amp mo 83m um: osu wcHucommHmmu mmsHm>«« .uwme wwamm mHnHuHsz m.amoaaa msu an Ho>mH Nm ms» um acouomme hHuamUHmHame uo: mum muouuoH :oaBoo nuHs mcstou aHnuHB mama: a m o.mmm m c.0wH w m.Hm peace uoa w m.oom m o.mNN o w.No N v c.mwN w H.HNH n m.N¢ H to o.ooN o m.NOH n c.0q N\H mN.o o o.NqN o m.ma n m.mq N a H.NNH n o.Nm m N.NN H m N.wo m m.Nm «am N.mH N\H m.N IIIIIIIIII we Amxmmav AEUV mxom3 o mxoma q mxmms N zocoavmuw uanms wcHBoz waHuuso «unwamz sun .coHumHuHcH assaumouu umumm mxmos o mam .q .N um mmmuwman hxoauaox .:0Humz. wCH3oE soumm nuaouwou uoc Gnu co mocoavmum mam wcHaoB mo uoowwm och .m DHnma 22 .ummH mwamm mHmHquz m.cmuasa mnu m0 Hm>mH Nm mnu um ucouowva zHucmonchHm uoc mum mumuumH canou nuHB mcadHoo cHnuHa mamozs m N.m m N.0 m 0.0 m 0.0 m m.NH w o.NH 06308 uo: m N.0 m o.0 m N.m m w.m m m.HH 0m 0.0N N m 0.0 m N.0 nm 0.0 A m.w m m.NH 0m m.NH H mm m.m 0m m.0 0 0.0 o 0.MH n 0.mH 0 o.NN N\H mN.0 m 0.0 m 0.0 pm 0.N a o.m m m.mH n m.NN N m 0.0 m 0.0 0w 0.0 0 0.0N 0 m.mN o o.Nm H o N.m 0 H.w 6 «.0H m n.0N o o.Hm 0 N.Nm N\H m.N II HI»: Wham Noowfi I Amxmmsv A800 mxmos 0 mxoo3 0 mxmma N mxoma 0 mxmms 0 mxoos N mucosvouw uanm: waaaoz @2330 am *zm .:0HuMHuH:H ucoaummuu umuwm mxmoa 0 0mm .0 .N um mmmuwoan zxo=uaox :oHuoz :H Aamv coHumanmmu xumv 0am Azmv mHmwnuahmouonm uoc co accoscoum 0am uanmn waHBoa mo uoowwm wsH .0 DHan 23 m.cmuc:o msu an am>ma am .uanms Nam Hmuou no 0ommn unmoumm uaomouawu mmsHm>«« .umma mmamm mHmHuHaz mzu um ucouomew NHusmoHMHame uoc mum mumuuoH aoafioo zuHB maasHou aHnuHs mama: « o N 0 0m m mN 0 HM mm H 0 m0 0m 0N m oN m N 0 0m 0m wN on am 00308 go: o w 0 mm on wN m 0N o 0 0 m0 m «N m mN m N 0 00 m NN m Hm N 0 0 0 Nm u on 6 mm a N no 00 pm NN 0m Hm m c on mm mo mm 00 mm H 0 m 0 Nm 0 mN on mm m o 0 cm on cm 0 0m m o 0 Hm on NM 0 Nm NNH mN.0 0 m u mm was NN n om 0 N on Nm 0m 0N m wN m o o Nm am on mm mm N m N 0 mm 0 0m 0 cm m o on 0m 0 mm m mN m o 0 mN 0 0m on mm H m N m HN m N0 0 mm m o m mN 00 mm o Nm m o m NH 0 00 «*0 N0 N\H m.N IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIN I Amxooav A800 NHcm mo>moH waoum muoom NHnm mm>mma mamum muoom «Ham mm>mma mawum muoom Nuaonvmum ustmn mxmo3 0 mxooa 0 mxmm3 N waHaoz waHuuao «ustos mum mo cOHuanuume unmouwm .cOHumHuHcH ucmaummuu Houwm 3:53 0 0mm .0 .N um mmmuwman axoaficmx £0.73: a« 3.2.3 mmaonfiau 0am .mo>MOH .mamum .muoou cH uanoa Nam mo COHuanuumHm unmouom onu no Nocosvoum 0cm ustos maHBoa mo uoommo use .N mHan 24 m.:moa=a Gnu Np Ho>mH N0 .aoHumuomuoocH NuH>HuomoH0mu Hmuou mo ucmuuom mnu uaomoummu mosz>«* . Ema. owned maaauasz mgu um uCGHDMMHv NHuamonchHm uo: mum mumuumH coaaou nuHS mcasHou aHnuHa mama: « m m 0 N0 on 00 am mH m N 0 mm 0 N0 mu HH 0 N 0 mm 0 on 0 w 0maoa uo: 0 0 0 H0 0 m0 0 OH 0 N on mm on 00 0 m n N on an A on 00 OH N 0 m on 00 0 00 0 m m N on Nm 0 N0 00m MH m o 0 mm A a0 06 OH H on m 0 mm 0 00 pm 0H m o m mN 0m mm m 0H m o 0 mm 0 0n om NH N\H mN.0 o N n 00 0 m0 0 OH m m on mm m on 0 o m o 0 m0 0 m0 0 m N m H 0 Nm 0 N0 0m 0H m o 0 0m m Hm 0m 0H m o 0 0m on Nm om NH H m H m 0N m 00 m NH w o m mN m Nm m mH m o m NN m m0 «ans mH N\H m.N II II IINIIIIIIIII I AmeGBV Aaov NHam mo>moq mamum muoom NHnm mm>mma maoum muoom NHnm mo>mmH mamum muoom hoamsuoum uanms mxmmz 0 mxoms 0 mxmoa N waHsoz waHuusu « ___ufl u”. Iu0H um gunu _H:umnfi uamuumm .dOHuMHuHaH unmaummuu umumm mxom3.0 0cm .0 .N um ammuwman Nxoauaox coHuoz cH AuHsuv mmeoquu 06m .mo>moH .mamum .muoou . Gnu :H mumzuahmouonan0H mo cOHunnHuumHv ucoouoa osu so Nocoavoum 0am uanmn waHaoa mo muuomwo may .0 DHan 25 .mGOHumoHHamu omunu 00 came Gnu ucmmmammu mmsHm>«« .mus o um woumHuHcH mma ucmaummwu mcH3oz« .2: mi.» «N 00 00 V0 0* NV on On 1N o. N. 0 I I 1 I I I I I I I .0. «.mmmuwoan axosucox GOHuoz :H voHuom u: NN m uo>o 0mu0uacoa COHuMHHamou xwmp co AucwHo: wcHuuso Eu m.NV wsHBoa mo uowmmo 058 .H muame CHAPTER 2 THE EFFECT OF STAGE OF DEVELOPMENT ON PHOTOSYNTHESIS, DARK RESPIRATION, AND DISTRIBUTION OF 14C-PHOTOSYNTHATE IN MERION KENTUCKY BLUEGRASS (POA PRATENSIS L.) AND PENNLAWN RED FESCUE (FESTUCA RUBRA L.) Abstract The effects of stage of development on net photosynthesis, dark respira- tion and distribution of 14C-photosynthate in Merion Kentucky bluegrass (Poa pratensis L.) and Pennlawn red fescue (Festuca rubra L.) were evaluated. Lateral shoot development occurred after the third (3 weeks after seedling emergence) and fifth leaf stage (3 to 4 weeks after seedling emergence) in Pennlawn red fescue and Merion Kentucky bluegrass, respectively. Tillers were initiated in the axils of leaves below fully expanded leaves in both spe- cies. Tiller development preceded rhizome initiation in red fescue; whereas, tillers and rhizomes were not initiated preferentially to one another in Merion Kentucky bluegrass. High dark respiration rates and a large percentage of leaf dry weight occurred at the first sampling period. The percent distribution of 14C-photosynthate shifted from the leaves to stems between the second and third week after seedling emergence in Kentucky bluegrass; whereas, this shift occurred between the third and fourth week after seedling emergence in red fescue. The stem fractions were the dominant sinks for photosynthate after the second and third week following seedling emergence in Pennlawn red fescue and Merion Kentucky bluegrass, respectively. The changes in these morphological and physiological responses during seedling growth may indicate critical developmental periods. 26 27 Introduction Effective turfgrass management requires knowledge of the physiological and morphological changes associated with its growth and development. Rapid,_ successful turfgrass establishment is required for effective dust and erosion control. Delays in establishment will increase the likelihood of soil loss by erosion. Few turfgrass investigations have described the physiological plant responses associated with growth and development. DeFrance and Simmons (7) briefly characterized the relative growth patterns of three cool season turf— grasses during seedling development. Tiller and rhizome development has been correlated with the early stages of turfgrass growth and shown to be dependent on species and environmental conditions (3. 4, 11). The photosynthetic-respiratory balance can be a critical factor during plant growth and develOpment. Net photosynthesis and dark respiration have been reported to vary independently from the stage of plant maturity (5, 9, l7). Photosynthate distribution depends on assimilate supply and demand and usually reflects areas of active metabolism (5, 6, l4). Carpenter (5) measured photosynthate distribution during seedling growth in dicotelydons and reported a gradual shifting of metabolic activity from leaves to stems and finally to roots. Nyahoza (12) reported enhanced movement of photosynthate into develOping rhizomes during seedling growth in Kentucky bluegrass. The objectives of this study were to investigate the morphological and physiological changes occurring during seedling develOpment in turfgrass. Net photosynthesis, dark respiration, and distribution of 14C-photosynthate were measured in order to estimate the energy balance and monitor shifts 28 in metabolic activity within the plant. Plant age, leaf stage, and leaf positioning were also measured during the various phases of lateral shoot development. This information could provide insight into more effective establishment practices and an understanding of the development patterns associated with turfgrass growth. Materials and Methods Cultivars of Merion Kentucky bluegrass and Pennlawn red fescue were selected based on their dominant use in temperate regions. Plants of each species were grown from seed in 5 cm diameter by 15 cm deep plastic con— tainers filled with washed silica sand and having perforated bases for free drainage. Each specie was seeded at 15 to 20 seeds per pot and the seedlings thinned gradually to one plant per pot at the end of 4 weeks. The higher plant density provided sufficient plant material for accurate sub-sampling during the early growth stages. Later thinning was done to minimize competi— tion and reduce interleaf shading during photosynthetic measurements. The germinated seedlings were grown in an environmental growth chamber at 23 C day and 16 C night temperatures. Light radiation level was 1000 DE M"2 sec'l. Relative humidity ranged between 65 to 75% and the photo- period was 14 hours. A nutrient solution drench (8) was applied every third day and plants irrigated with tap water on alternate days. Weekly clipping was initiated 4 weeks after seedling emergence at a height of 7.6 cm. Photosynthesis, dark respiration, and distribution of 14C-photosynthate were measured using methods previously described (10). The plants were returned to the environmental growth chambers after labelling for a 24 hour period. The root system was washed free of sand, immediately frozen with dry ice, and stored in a -10 C freezer. Plants were subsequently sectioned into leaf, root, stem, and rhizome fractions and freeze dried. 29 The leaf fraction consisted of leaf tissue located above the collar. The crown and leaf sheath were included in the stem fraction. Root segments were removed from below and immediately adjacent to the crown. The rhizome fraction consisted of subsurface secondary lateral shoots that developed extravaginally and extended horizontally. Only those rhizomes that emerged into the light and formed photosynthetically active leaf tissue were separated into leaf and stem fractions. Leaf area measurements were made with a LI-COR, Model LI-3000 portable area meter using a subsample of fresh leaf blades (5 to 10). Measurements were taken weekly and a leaf area :leaf weight ratio was determined for calculation of total leaf area. Each measurement was replicated three times on separate plants and a completely randomized block analysis of variance used. Differences between treatment means were tested statistically using Duncan's Maltiple Range Test. Results and Discussion Pennlawn red fescue initiated lateral shoots only after the third leaf stage of develOpment (approximately 3 weeks after seedling emergence). Merion Kentucky bluegrass initiated lateral shoots after the fifth leaf stage (approximately 3 to 4 weeks after seedling emergence). These results indicate that a specific level of maturity or developmental stage is required before lateral shoot development can occur. Soper (16) also reported dis- tinct levels in maturity at which tillers were initiated in perennial rye- grass (Lolium_perenne L.) 30 Tiller development in both species occurred only in the axils of leaves below fully expanded leaves. Similar leaf positioning has been reported in other grasses undergoing tiller development (13). Tiller development in red fescue preceded rhizome initiation in all observations. However, in Merion Kentucky bluegrass, neither tillers nor rhizomes were initiated preferentially to one another. The percent distribution of dry weight during turfgrass seedling development is shown in Table 1. Both species showed similar distribution patterns. The percent distribution of dry weight in the root fraction tended to increase from the initial sampling to 3 weeks after seedling emergence. The leaf fraction showed enhanced percent dry weight accumulation during the first 2 weeks. This trend was followed by some slight differences, however, these variations did not follow a noticeable trend in either species. The proportion of dry weight in the stem fraction in Merion Kentucky bluegrass increased gradually from the second sampling period to the eighth week of development. The percent of stem dry weight dropped at the last sampling period and corresponds to a significant increase in rhizome growth. These changes in the percent dry weight distribution reflect inherent shifts in the develOpmental growth pattern. This type of information should provide a greater understanding of turfgrass growth and develOpment. Variations in net photosynthate and dark respiration during the ten week sampling period were similar for both species (Table 2). Higher photo- synthetic rates occurred at the initial sampling period only. Dark respira— tion rates were accelerated l and 2 weeks after seedling emergence. Rates were greatest one week after emergence and declined to one-half the original level at the second sampling period. This initial acceleration in respiration may indicate a time sequence of high energy demands. Heightened photosynthetic 31 rate at the initial sampling period corresponded with a high percent leaf dry weight and may indicate a plant response designed for high photosynthate output. The percent distribution of photosynthate shifted significantly from the leaves to the stems in both species (Table 3). This shift occurred between the third and fourth sampling periods in Pennlawn red fescue and second and third sampling periods in Merion Kentucky bluegrass. Rhizome development followed 1 week after and this shift in distribution may be a factor re- lated to the initiation of secondary lateral shoot development. The percent distribution of 14C—photosynthate in the root fraction declined during rhi— zome development in both Merion Kentucky bluegrass and Pennlawn red fescue. Rhizome development has been shown to act as a noticeably strong sink within plant systems and alters photosynthate distribution (6, 12). The relationship between rhizome development and decline in percent accumulation of photo- synthate in the roots may indicate that rhizome development occurs at the expense of root growth. The stem fraction showed a high percentage of 1[‘C-photosynthate accumulation. Stem tissue has been reported as a major region of carbohydrate storage in grasses (l, 2, 15). Proper selection of planting dates for optimal environmental growth conditions (15-20 C) and cultural practices for adequate moisture and nu- trient availability during these marked changes in seedling development may be an important key to rapid and successful turfgrass establishment. 10. 11. 32 Literature Cited Adegbola, A. A. and C. M. McKell. 1966. Effect of nitrogen fertiliza- tion on the carbohydrate content of coastal bermudagrass (Cynodon dactylon L. Pers.). Agron. J. 58:60—64. Alberda, T. 1957. The effects of cutting, light intensity, and night temperature on growth and soluble carbohydrate content of £91123 perenne L. Plant and Soil. 8:199-230. Alburquerque, H. E. 1967. Leaf area, and age, and carbohydrate reserves in the regrowth of tall fescue (Festuca arundinacea Schreb.) tillers. Ph.D. Thesis. Virginia Polytechnic Institute. pp. l-278. Areda, H., R.E. Blaser and R. H. Brown. 1966. Tillering and carbo- hydrate contents of orchardgrass as influenced by environmental factors. Crop Sci. 6:139-143. Carpenter, S. L. 1971. Developmental changes in assimilation and trans- location of photosynthate in Black Walnut (Juglans nigra L.) and Honeylocust (Gleditsia triacanthus L.) seedlings. Ph.D. Thesis. Michigan State University. pp. 1-85. Crafts, A. S. and C. E. Crisp. 1971. Phloem transport in plants. W. H. Freeman and Co., San Francisco, Calif. pp. 127—156. DeFrance, J.A. and J. A. Simmons. 1951. Relative period of emergence and initial growth of turfgrasses and their adaptability under field condition. Proc. of the Am. Soc. for Hort. Sc. 57:439-442. Hoagland, C. R. and D. I. Aron. 1950. The water culture method for growing plants without soil. Calif. Agri. Expt. Sta. Circ. 347 pp. 32. Kortschak, H. P. and A. Forkes. 1969. The effect of shade and age on the photosynthesis rate of sugar cane. In: Metzner, H. (ed.): Progress in Photosynthesis Research. Vol. 1 pp. 383-387. Krans. J. V. 1975. The effects of cutting height and mowing fre uency on net photosynthesis, dark respiration, and distribution of 4C- photosynthate in Merion Kentucky bluegrass. In: The effects of cutting height and mowing stage of develOpment, and reduced light intensities on net photosynthesis, dark reSpiration, and distribution of 14C-photosynthate in cool season turfgrasses. Chapter 1. Ph.D. Thesis. Michigan State University. Mitchell, K. J. 1953. Influence of light and temperature on the growth of ryegrass (Lolium spp.). II. The control of lateral bud develop- ment. Physiol. Plant. 6:425-443. 12. 13. 14. 15. 16. 17. 33 Nyahoza, J. L. 1973. The interrelationship between tillers and rhizomes of Poa pratensis L. - an autoradiographic study. Weed Sci. 21:304—309. Patel, A. S. and J. P. CoOper. 1961. The influence of several changes in light energy on leaf and tiller development in ryegrass, timothy and meadow fescue. J. of the British Grassland Soc. 16:299-308. Quinland, J. D. and G. R. Sagar. 1969. An autoradiographic study of the movement of 14C—labelled assimilates in the developing wheat plant. Weed Res. 2:264—273. Smith, D. 1968. Carbohydrates in grasses. IV. Influence of tempera- ture on the sugar and fructosan composition of timothy plant parts at anthesis. Crop Sci. 8:331-334. SOper, K., and K. J. Mitchell. 1956. The developmental anatomy of perennial ryegrass (Lolium perenne L.). New Zealand J. of Sci. and Tech. Sec. A. 37:484-504. Wilson, D. and J. R. Cooper. 1969. Apparent photosynthesis and leaf characters in relation to leaf position and age, among contrasting Lolium genotypes. New Phytol. 68:645-655. 34 .uanos uamHa .ummH owamm oHQHuHaz m.amoa:a ecu N0 Ho>oH Nm one um unsymmmHv NHuamonchHm no: mum muouuoH coeaou nuHa Ammouomv mSou cHnuHs mamoz«« Hmuou no woman uanma Nuv unmouoa mnu ucommuaou mosHm> « o 0 0 m a m m N m N m H o o m o m o moaoNHsm mmmummsHa o as 0 am 0 an o cm 0 as a as a as m on m am mm>mma sausages on 0N 0 cm 00 0N 00 wN 06 NN a NN 0m 0N m NH 0m 0N msmum coHuoz on mN on on on Nm 6 mm on on on on 0 0m 0 NN m HN muoom 0 0 m H m H m H m H m o m o m o m o mmaoNHnm on N0 up 00 on 00 on m0 6 wm 0 00 0 00 m mm m Nm mo>mmH msommm 06H m 0N m mN 0m HN 0m MN m 0N 0m HN 0 NH 0 NH m 0N macaw cBchamm 000 Nm on cm 060 0m 000 mm 00 mm 000 mm 00 0m 0 oN «am NH muoom IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII NIIIIIIIIIIIIIIIII'I Ill 0H m N m 0 m N H osmmHH moHooam Ax3v voHumm wcHHaamm ucmHm «ustoa Nam 00 cOHuanuumHn ucmoumm .mmmawoan axosucmx :oHuoz 0cm Daemon pow cschcom CH unwaoa Nam mo coHuanwumHv ucouuoa msu co unmam0Ho>o0 mo mwmum 00 avenue one .H mHan 35 .umoH owamm mHaHuHsz m.amoa:n onu N0 Hm>mH NM mnu um acoummev NHuchHMchHm uoc mum mumuumH aoEEoo nuHs Ammouomv m3ou aHnuHa mammz« o m o 0 o m o 0 o 0 o m o m 0 M m 0H am mmmuwoaHA Nxoauamx a «a a aa a ma a ma a sa a aa a ea a ma m an zm cease: as um um as us as om .: mma pm osomow wow 0 NH on oN on oN on HN on oN 0 0N on NN on MN m H0 zm camHacmm IIIIIIIIIIIIIIIIIIIIIIIIIIIIII aIae Nwee Noowz I III OH M N 0 m 0 M N H uamaousmmwa mmHuomm AHBV voHuma wcHHaEmm quHm «coHumuHammu xumv 0cm meocuczmouosm umz .oaomom vow cschcom 0cm mmmuwDSHn qusucmu cOHuoz aH Aamv coHumuHmmou xumv 0cm Azmv UHuonucszuosm um: msu so uno8mon>o0 mo mwmum mo uumwwm any .N mHnma 36 .ummy mwamm mHaHuHsz m.amoaao N0 Hm>oH NM Gnu um ucoumwva NHucmoHMHcMHm uoc mum muouumH GOEEoo nuHB Ammouomv m30u cHsuHS mammz«« .ucmHm you :OHumuomuoocHIo0H HauOu no woman NuH>HuomoH0mu udmoumm onu ucommuamu moaHm> N o M 0 M 0 0 n 0 m H m H m o m o m o moaoNHsm mmmuwman u as cu an eu.mm so cm m on so mm we mm m as m as mm>mma sausages on N0 0 HM 0 HM 0 HM 0 MM 0 MM 0 0M m NN m ON msmum aoHuoz o M on 0H 6 N o m m 0H 0m 0H m NH m 0H m MH muoom m N m N m H m H m H m o m o m o m o mmaoNHnm GM 00 60 MM Mo 00 av HM o0 oM o0 NM a N0 0 MM m N0 mo>moH maumom 0mm 0 MM 00 MM on M0 on HM 060 MM on M0 0m NM m MN m 0N maoum :3MHsaom 0 CH 0 0H 0o NH on NH 060 0H 0 MH 0m HN 0 MN ««m NN muoom OH M N 0 M 0 M N H osmmHu mmHooam Hx3v voHumm MGHHmEmM ucmHm «mumsucszuosan0H Mo :oHuankumHv ucmuumm .mmmuwwaHn Nxosucmx :OHumz 0am wsommw 0m» cschamm cH mumnucxmouonmIo0H mo GOHuanuumHU unmouoq ozu :o ucmaaoHo>m0 mo wwmum mo uoowwm 638 .M anmB CHAPTER 3 THE EFFECT OF REDUCED LIGHT INTENSITY ON NET PHOTOSYNTHESIS, DARK RESPIRATION, ROOT RESPIRATION, DISTRIBUTION OF l4c-PHOTOSYNTHATE AND RELATIVE RATE OF 14C-PHOTOSYNTHATE TRANSLOCATION IN SIX COOL SEASON TURFGRASSES Abstract The effects of reduced light on net photosynthesis, dark respiration, root respiration, distribution of 14C-photosynthate and relative rate of l4C-photosynthate translocation were initiated in six cool season turf- grasses showing several degrees of shade tolerance. All cultivars, except Wintergreen showed a high percentage of root dry weight at the lowest light intensity. Net photosynthetic rates declined as light intensity was de- creased in all species. No significant differences in dark respiration rates occurred among cultivars as light intensities decreased. However, Pennlawn and Wintergreen tended to decline as light intensities were lowered. Root respiration rates increased as light intensity decreased in all cultivars determined with washed root samples. Nugget and A-34 showed a high percen- tage of 1l‘C-photosynthate incorporation in the stem fractions and reduced movement of labelled assimilates out of the leaves. The relative rate of 14C-photosynthate translocation was variable depending on species tested. All cultivars responded similarly or lacked definite trends at reduced light intensities in terms of net photosynthesis, dark respiration, root respiration and relative rate of ll‘C-photosynthate translocation. The high accumulation of lac—photosynthate in the stem tissue in Nugget and 37 38 A—34 Kentucky bluegrass at the lowest light intensity may be associated with a shade adaptive mechanism. This study did not reveal conclusive trends or similarities between cultivars indicative of possible shade adaptive mechanisms. Introduction Red fescue (Festuca rubra L.) is a shade adaptive cool season turf— grass species (5,29). Past investigations have usually reported poor shade tolerance for Kentucky bluegrass (Poa pratensis L.) (4, 29, 30). Recently, two improved cultivars of Kentucky bluegrass (Nugget and A-34) have shown excellent shade tolerance under field conditions (6). Shade adversely alters the microenvironment for turfgrass growth and development. The most obvious effect of shade is reduced light intensity. Low light levels have been reported to reduce net photosynthesis, dark respiration, light compensation points, and light saturation levels (3, 8, 9, 10, 11, 12, 13). Higher light saturation levels and light compensation points have been used to classify plants as "sun" or "shade" species (12). Wilkinson, Beard, and Krans (30) recently investigated these responses at reduced light intensity in Pennlawn red fescue and Merion Kentucky blue- grass. They showed no significant differences in the net photosynthetic rates, light compensation points, or light saturation levels between species. However, dark respiration was significantly lower in Pennlawn compared to Merion at the lowest light level (2.7 Klux). They concluded that a more favorable photosynthetic-respiratory balance which may contribute to the persistence of Pennlawn in shade. Root respiration rates have been shown to vary in creeping bentgrass (Agrostis palustris Huds.) depending on the strains tested and temperature (21), 39 The degree of root respiration may be a significant factor influencing the photosynthetic-respiratory balance. Shade adaptation of several species has been related to an improved photosynthetic—respiratory balance (11, 13). The close interrelationship between assimilate translocation and light intensity is well established (13, 16, 24, 27, 28). Crafts (16) indicated that the influence of light on assimilate translocation is indirectly re- lated to photosynthesis by the "supply of osmotically active solutes which drive the osmotic pumps." Hartt (17) has proposed that the translocation of assimilates is directly controlled by light which may not involve pressure flow. She (18) reported the translocation of l4C-labelled assimilates to be differentially stimulated by selected spectrums of light quality. Nelson (24) showed greater transport of 14C-assimilates from shoots to roots in Pings seedling grown in full sunlight versus plants under lower light levels (6% full sunlight). This effect was not observed in plants grown at full sunlight prior to sampling at reduced light intensities. This relationship may indicate that the influence of light on translocation is indirectly related to light intensity. Greater translocation of assimilates usually occurs during the light (15, 18, 26) period. However, investigators using different plant species showed greater movement of assimilates into the root systems during the dark (20, 23, 25) period. Brady (13) reported that the effect of reduced light intensity on the distribution of foliar applied 2,4,5-T varied de- pending on the species tested. The objectives of this study were to measure net photosynthesis, dark respiration, root respiration, distribution of 14C-photosynthate and relative rate of 14C-photosynthate transport at reduced light intensities in shade adapted and unadapted turfgrasses. This information may further elucidate mechanisms of shade adaptation in turfgrasses and prove useful in the selection of improved turfgrasses suitable for growth in the shade. 40 Materials and Methods Turfgrass cultivars used in this study were selected on the basis of evaluation trials conducted under a dense shade tree canopy at Michigan State University (6). Four turfgrass cultivars showing shade tolerance [Nugget Kentucky bluegrass, A—34 Kentucky bluegrass, Pennlawn red fescue, and Wintergreen chewings fescue (Festuca rubra var. commutata Gaud.)] and two shade intolerant cultivars (Merion Kentucky bluegrass and Park Kentucky bluegrass) were grown from seed in 5 cm diameter by 15 cm deep plastic containers filled with washed silica sand. Each cultivar was seeded at 5 plants per pot and thinned to one plant following emergence. Precondi- tioning light intensities of 1200,300, and 110 DE M"2 sec"1 (43.0, 10.0, and 3.0 Klux, respectively) were initiated in separate growth chambers upon seedling emergence. Temperatures within growth chambers were main— tained at 23 C day and 16 C night temperatures. A photOperiod of 14 hr and relative humidity of 70+5% was maintained in the growth chambers throughout the study. Plants were mowed weekly at 6.75 cm beginning at the fourth week following emergence. A nutrient solution drench (19) was applied every third day and plants irrigated with tap water on alternate days. Containers were perforated to provide free drainage. Light intensity treatments were selected on the bases of previous re- search (29). Light radiation levels were measured with a Lambda LI-170 radiometer. Light treatments were established by adjusting the relative proportions of fluorescent to incandescent bulbs and raising or lowering the chamber shelves. Light quality was monitored with an ISCO Model SR spectroradiometer. Only slight differences in light quality were observed among growth chambers throughout the study. Plants were grown under each light intensity for 8 weeks prior to sampling. Variations in confounding 41 factors such as light quality, soil moisture, soil temperature, and disease were controlled or eliminated during the study. Photosynthesis, dark respiration, and distribution of 1(‘C-photosynthate were measured according to methods and conditions previously described (22). Net photosynthetic rates were measured at the preconditioning light intensity. Total radioactive plant incorporation was similar among cultivars (1 uCi 140). The relative rates of assimilate transport were determined by monitoring the degree of radioactive movement at 0.5 and 2 hour intervals following labelling. The relative rate of translocation was determined at the lowest light level (110 uE M52 sec-1) only. This light treatment was selected as a means of indicating possible similarities or trends among shade tolerant cultivars. Labelling (5 uCi of ll'COZ for 15 min) was conducted according to procedures previously described (22). Plants were returned to the growth chamber (110 uE M"2 sec'l) for the specified time interval (0.5 or 2 hours) before harvesting. The amount of labelled photosynthate incorporation into the root, stem, leaf, and rhizome fractions was determined by combustion methods previously described (22) . The rate of photosynthate transport was also monitored by radioautography. Plant materials were prepared for determination of distribution patterns and rate of transport of 1l’C-photosynthate by washing the root system free of sand, immediately freezing with dry ice and storing in a -10 C freezer. Plants used for combustion analysis were separated into root, stem, leaf, and rhizome fractions and freeze dried. Plants used for determining the rate of translocation were further subdivided into an upper and lower root fraction. The upper fractions consisted of roots immediately below the crown and downward to a distance of 1/2 the total root length. The lower fraction included the remaining roots. The leaf fraction consisted 42 of leaf tissue located above the collar. The crown and leaf sheath were included in the stem fraction. Root segments were removed below and imme- diately adjacent to the crown. The rhizome fraction consisted of subsurface secondary lateral shoots that develOped extravaginally and extended horizontally. Only those rhizomes which emerged into the light and formed a photosynthetically active leaf area were separated into leaf and stem fractions. Root respiration rates were estimated by two methods. Root respiration measurements were made on plants prior to harvesting for determining the distribution of labelled photosynthate. Plants were defoliated at the sur- face of the sand. The container of sand plus roots was placed in the C02 exchange system and the rate of C02 evolution monitored. Following this measurement, roots were washed from the sand. The container with sand only was allowed to drain free for 24 hours, and then placed in the C02 exchange system for determining the rate of C02 evolution. The washed roots were placed in the C02 exchange system and their rate of respiration measured. The rate of C02 evolved from the sand plus roots minus the sand provided ano- ther estimation of root respiration. MeasurementscfifCOz evolution were made over a 15 min time interval for both sampling methods. The rate of 002 evolution was measured 3 minutes after the system was closed. This time coincided with an initial linear portion of the root respiration response. Leaf area measurements were made with a LI-COR, Model LI-3000 portable area meter using a sub-sample (5 to 10) of fresh leaf blades. A leaf area: leaf weight ratio was determined for calculation of the total area. Each measurement was replicated three times on separate plants and a factorial analysis of variance used. Differences between treatment 43 means and main effects of light intensity and cultivar were tested statistically using Duncan's Multiple Range Test. Results and Discussion Total dry weight accumulation in the root, stem, and leaf fractions declined as light intensity decreased in all cultivars (Table 1). No noticeable differences were measured in the stem and leaf dry weight frac- tions among cultivars at the three light intensities. The greater root development in both fescue cultivars may indicate a more extensive root system for nutrient and moisture uptake at reduced light intensities. Rhizome development tended to decline as light intensities decreased in all rhizomatous grasses. A-34 Kentucky bluegrass showed significantly greater rhizome develOpment at the highest light intensity. Park and A-34 Kentucky bluegrasses showed higher total dry weight accumulation at the 1200 DE M‘Zsec"1 light level compared to the other Kentucky bluegrasses. This may be related to reports indicating a rapid seedling establishment rate for Park and A-34 (6). No consistent trends or similarities in the percent distribution of dry weight were found among species at the three light intensities in the stem and leaf fractions (Table 2). Merion, Park, and A-34 showed a high percentage of dry weight accumulation at the intermediate light intensity in the rhizome fraction. These cultivars have been shown to be vigorous sod formers (7). There were no noticeable trends in the distribu- tion pattern of dry weight at the three light intensities between Kentucky bluegrass and fescue or among Kentucky bluegrass cultivars that would indicate a morphological response associated with a shade adaptive mechanism. 44 The percent distribution of 14C-photosynthate did not follow consistent trends as light intensity decreased in the root, stem, and leaf fractions (Table 3). Pennlawn showed the greatest proportion of ll"(I-photosynthate accumulation in the root fraction at the lowest light intensity. Nugget and A-34 showed a high percent incorporation of labelled photosynthate in the stem fractions at the lowest light intensity. This trend was associated f 14 -photosynthate out of the leaf fraction. The with increased movement 0 stem tissue has been shown to be dominant region of carbohydrate storage in grasses (1, 2). This relationship between the stem tissue as an area of carbohydrate storage and high assimilate accumulation at low light intensi- ties may be a response unique to these shade tolerant cultivars. The relative rate of 14C-photosynthate transport measured at the lowest light intensity was variable depending on the cultivar tested (Table 4, Figures 1, 2, and 3). Pennlawn, Wintergreen and A-34 tended to show reduced incorporation of l4C-photosynthate in the upper root fraction 1/2 hour after labelling. Nugget showed the high incorporation of 14C- photosynthate into the upper root fraction 1/2 hour after labelling. Trans— location of labelled photosynthate into the roots was noticeably higher in Pennlawn and Wintergreen 2 hours after labelling. The Kentucky bluegrasses showed increased translocation of 1l'C—photosynthate into roots 2 hours after 1l'C-labelling, however no marked similarities or differences were measured among shade tolerant and intolerant cultivars. Pennlawn showed significantly greater movement of 14C-photosynthate out of the leaf fraction 2 hours after 14C-labelling and was associated with an enhanced accumulation in the stem fraction. The relative rates of assimilate translocation at reduced light intensity did not reflect trends among shade tolerant or intolerant cultivars. 45 Net photosynthetic rates declined as light intensity decreased in all six cultivars; whereas, dark respiraton tended to decline slightly (Table 5). Larger reductions in net photosynthesis occurred between plants grown at 1200 DE M"2 sec'1 and 300 DE M"2 sec-1. There were no significant differences in the net photosynthetic and dark respiration rates among shade tolerant or intolerant cultivars at the three light intensities; however, dark respiration rates tended to decline in both fescue cultivars. Wilkinson .E£.§l- (30) measured significant reductions in the dark respiration rates in Pennlawn at reduced light intensities for individual plants, but not in swards. This difference in dark respiration rates between awards and indi- vidual plants was in part attributed to greater C02 diffusion resistance in the canopy. The apparent cause of this inconsistency between studies is unknown and requires further investigation. Root respiration rates determined with washed root samples tended to increase as light intensity decreased in all cultivars (Table 6). There were no consistent trends among cultivars in root respiration measurements taken from root plus sand samples at the three light intensities. Neither method showed differences in the root respiration among cultivars which could attribute a more favorable photosynthetic-reSpiratory balance. The results of this study provides new information surrounding possible mechanisms of shade adaptation in turfgrasses. Conclusive evidence relating directly to shade tolerance was not revealed, however, specific trends were monitored which may lead to further investigations of shade adaptive mechanisms. 10. 11. 12. 13. 46 Literature Cited Adegbola, A. A. and C. M. McKell. 1966. Effect of nitrogen fertiliza- tion on the carbohydrate content of coastal bermudagrass (Cynodon dactylon L. Pers.). Agron. J. 58:60-64. Alberda, T. 1975. The effects of cutting, light intensity, and night temperature on growth and soluble carbohydrate content of Lolium perenne L. Plant and Soil. 8:199-230. Alexander, C. W. and K. E. McCloud. 1962. C02 uptake (net photo- synthesis) as influenced by light intensity of isolated bermuda- grass leaves contrasted 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. Agron. J. 57:457-459. Beard, J. B. 1973. Turfgrass: Science and Culture. Prentice-Hall, Inc., Englewood Cliffs, N.J. p. 181-209. Beard, J. B. 1968. Kentucky bluegrass cultivar and blend evaluations. In: Michigan Turfgrass Report. 3:2-3. Beard, J. B. 1972. Comparative sod strengths and transplant sod rooting of Kentucky bluegrass cultivars and blends. In: 42nd Annual Michigan Turfgrass Conference Proceedings. 1:123-125. Bjorkman, O. 1968. Further studies on differentiation of photosyn- thetic properties 1J1 sun and shade ecotypes of Solidag9_virgaurea. Physiol. Plant. 21:1-10. 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, O. and P. Holmgren. 1966. Photosynthetic adaptation to light intensity in plants native to shaded and exposed habitats. Physiol. Plant. 19:854-859. Bjorkman, 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., 1071-1072. p. 94-102. Bohning, R. H. and C. A. Burnside. 1956. The effect of light intensity on rate of apparent photosynthesis in leaves of sun and shade plants. Am. J. Bot. 43:557-561. Brady, H. A. 1969. Light intensity and absorption and translocation of 2,4,5-T by woody plants. Weed Sci. 17:320-322. 14. 15. l6. l7. 18. 19. 20. 21. 22. 23. 24. 25. 26. 47 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. Butcher, H. C. 1965. The kinetics of carbon—l4 translocation in sugar beets: an effect illumination. Dissertation Abstr. 25:7350. Crafts, A. S. and C. E. Crisp. 1971. Phloem transport in plants. W. H. Freeman and Co., San Francisco, Calif. pp. 127-156. Hartt, C. E. 1965. Light and translocation of 14C in detached blades of sugar cane. Plant. Physiol. 40:774-781. Hartt, C. E. 1966. Translocation in colored light. Plant Physiol. 41:369-372. Hoagland, D. R. and D. I. Arnon. 1950. The water culture method for growing plants without soil. Calif. Agr. Exp. Stat. Circ. 347 p. 32. Hodgkinson, K. C. and J. A. Veale. 1966. The distribution of photo- synthate within lucerne as influenced by illumination. Aust. J. Biol. Sci. 19:15-21. Karnoc, K. J. 1974. Physiological characteristics of heat tolerant and susceptible creeping bentgrass (Agrostis palustris Huds.) M.S. Thesis, U. of Ariz. pp. 25. Krans, J. V. 1975. The effects of cutting height and mowing fre uency on net photosynthesis, dark respiration, and distribution of 4C- photosynthate in Merion Kentucky bluegrass. In: The effects of cutting height and mowing stage of development, and reduced light intensities on net photosynthesis, dark respiration, and distribution of 14C-photosynthate in cool season turfgrasses. Chapt. 1, Ph.D. Thesis, Michigan State University. Nelsonz C. D. 1964. The production and translocation of photosynthate C1 in conifers. In: "The Formation of Wood in Forest Trees," ed. by M. H. Zimmermann, Academic Press, New York p. 243-257. Nelson, C. D. 1963. Effect of climate on the distribution and trans- location of assimilates. In: "Environmental Control of Plant Growth," ed. by L. T. Evans, Academic Press, New York p. 149-173. Nelson, C. D. and E. C. Humphries. 1957. Uptake and translocation of C-14 labelled sugars applied to the primary leaves and soybean seedlings. Can. J. Bot. 35:339-347. Rhohrbaugh, L. M. and E. L. Rice. 1949. Effect of application of sugar on the translocation of sodium 2,4-dichlorophenoxy acetate by bean plants in the dark. Bot Gaz. 110:85-89. 48 27. Shen, G. M. 1960. Translocation and distribution of assimilates from the leaves of rice plants during its various developing periods- experiments with radioactive carbon (C14). Acta Agric. Sinica 11:30-40. (Biol. Abst. 35:4648-4649. 1960) 28. Thrower, S. L. 1962. Translocation of labelled assimilates in soybean II. The pattern of translocation in intact and defoliated plants. Aust. J. Biol. Sci. 15:629-649. 29. Wilkinson, J. F. and J. B. Beard. 1974. Morphological responses of Poa pratensis and Festuca rubra to reduced light intensity. In: Proceedings of the Second Ipternational Turfgrass Research Conference. Am. Soc. Agron. Madison, Wisc. pp. 231-240. 30. Wilkinson, J. F., J. B. Beard and J. V. Krans. 1975. Photosynthetic— respiratory responses of 'Merion' Kentucky bluegrass and 'Pennlawn' red fescue at reduced light intensities. Crop Sci. 15:165-168. 49 Table l. The effect of three light intensities on the distribution of dry weight in the roots, stems, leaves, and rhizomes in six cool season turfgrasses after 8 weeks of growth at preconditioning light intensities. Distribution of dry weight* Light Cultivar Radiation Roots Stems Leaves Rhizomes DE M"2 sec‘l Mg-- Merion 1200 388 d 300 ef 215 fg 12 abc 300 213 c 166 c 120 d 27 c 110 50 a 27 a 26 a 0 a Park 1200 486 e 360 g 473 j 27 c 300 110 b 93 b 97 cd 15 abc 110 43 a 29 a 20 a 0 a Nugget 1200 355 d 243 d 308 i 12 abc 300 162 c 147 c 164 e 5 ab 110 39 a 33 a 19 a 0 a A-34 1200 490 e 432 h 272 h 91 d 300 111 b 90 b 65 bc 23 bc 110 56 a 41 a 24 a 0 a Pennlawn 1200 508 e 331 fg 271 h 11 a 300 344 d 209 d 194 ef 0 a 110 85 ab 50 ab 28 a 0 a Wintergreen 1200 492 e 284 e 241 gh 0 a 300 179 c 150 c 113 d 0 a 110 76 ab 52 ab 44 ab 0 a *Means within columns with common letters are not significantly different at the 5% level by the Duncan's Multiple Range Test. 50 Table 2. The effect of three light intensities on the percent distri— bution of dry weight in the roots, stems, leaves, and rhi- zomes in six cool season turfgrasses after 8 weeks of growth at preconditioning light intensities. Percent distribution of dry weight* Light Cultivar Radiation Roots Stems Leaves Rhizomes uE M"2 sec-l % Merion 1200 **42 bcdefg 33 bcde 24 bc 1 a 300 41 abcdef 31 abcde 23 be 5 b 110 49 gh 26 a 25 bc 0 a Park 1200 36 abc 27 ab 35 d 2 a 300 35 ab 29 abcd 31 d 5 b 110 47 fgh 32 abcde 21 abc 0 a Nugget 1200 39 abcde 27 ab 33 d l a 300 34 a 30 abcd 35 d 1 a 110 43 cdefg 37 e 21 abc 0 a A~34 1200 38 abcd 34 cde 21 abc 7 be 300 39 abcde 31 abcd 23 bc 7 bc 110 46 efgh 34 de 20 ab 0 a Pennlawn 1200 46 efgh 30 abcd 23 be <1 3 300 46 efgh 28 abc 26 c 0 a 110 53 h 31 abcd 16 a 0 a Wintergreen 1200 48 fgh 28 abcd 23 bc 0 a 300 41 abcdef 34 cde 25 bc 0 a 110 44 defg 30 abcd 25 bc 0 a * Means within columns with common letters are not significantly different at the 5% level by the Duncan's Multiple Range Test. **Values represent the percent of the total dry weight. 51 Table 3. The effect of Ehree light intensities on the percent dis- tribution of 1 C-photosynthate in the roots, stems, leaves, and rhizomes in six cool season turfgrasses after 8 weeks of growth at preconditioning light intensities. Percent distribution of 14C-photosynthate* Light Cultivars Radiation Roots Stems Leaves Rhizomes uE M"2 sec.1 ---%--- Merion 1200 28 abc** 48 efg 23 f 1 a 300 25 a 55 gh 18 def 2 ab 110 40 efg 49 efg ll bc 0 a Park 1200 44 fgh 39 abc 15 cd 2 ab 300 30 abcd 50 fgh 15 cd 5 cd 110 43 fgh 46 def 11 bc 0 a Nugget 1200 27 ab 50 fgh 22 ef 1 a 300 36 def 41 bcde 20 def 3 abc 110 28 abc 62 i 8 a 0 a A—34 1200 26 ab 51 fgh 19 def 4 bc 300 35 cde 43 cdef 15 cd 7 de 110 34 bcd 58 hi 8 a 0 a Pennlawn 1200 45 gh 37 abc 18 def l a 300 47 ghi 37 abc l4 bcd 2 ab 110 53 i 31 a 16 cd 0 a Wintergreen 1200 51 hi 34 ab 14 cd 0 a 300 44 fgh 33 a 23 f 0 a 110 40 efg 43 cdef l7 cde 0 a * Means within columns with common letters are not significantly different at the 5% level by the Duncan's Multiple Range Test. **Values represent the percent of total radioactivity incorporated. 52 .wmumuomuoocH NuH>Huum0H0mu HmuOu mo ucmuuwm mcu ucmmmwamu mmsHm>a« .ummH mMcmM OHaHuHsz m.amocsa N0 Ho>OH NM onu um uGOHGNMHv NHuamonHcMHm uo: mum wumuumH soaaou auHB maabHoo manna: meme: I 0 c.0N on M.MH 0 M.M 0 o.N N m M.MM m M.M m M.o m N.H N\H comuwuoucHz m M.N0 m o.0N o M.M m M.M N ow 0.MM 0m o.MH m M.o m H.H N\H SBchcmm on o.0N ova N.MH 00m M.H on M.N N ow 0.MM 0m M.NH m 0.0 m o.H N\H 0MI< n M.NN ow 0.HN 00 0.N o N.M N mean a.mN eon n.0a one a.a on a.~ ~\a ummwsz 000 M.NN 000 H.NH on M.N o H.M H opo 0.MM 60m H.0H m M.o 0m N.H N\H xumm 0000 N.MM 000 M.0H 00m M.H 0 M.N N 0000 0.HM on N.MH 0m M.M «*0m M.H N\H COHHDZ lNlllll I IHSI mo>mmH mamum uoom uoom 00Humm mum>HuHso umaoa Home: :oHuMUOHmcmuH «mumnucMmOuosmIo0H wo COHusfiHuumHm uamuumm .meuHmcoucH unMHH MchOHqucoooum um nusouw mo mxooB M umumm mmmmmuwwusu common Hoou me :H mo>mmH 0cm .mEoum .muoou uoaoH .muoou woman mnu cH McHHHwan woumm m»: N van N\H um vmuzmmma uuomwcmuu mumnuchmouonan0H mo mumu m>HumHmu osu co moHuHmcmucH ustH momma mo uommwo onH .0 oHan 53 Table 5. The effect of three light intensrties on the net photo- synthetic and dark respiration rates in six cool season turfgrasses after 8 weeks of growth at preconditioning light intensities. Net* Dark Cultivar Radiation Photosynthesis Respiraton DE M‘2 sec"1 - mgCOz dm'2 hr-1 """ Merion 1200 18.4 gh 4.6 b 300 5.2 cd 4.1 ab 110 2.1 a 4.0 ab Park 1200 16.5 fg 5.2 be 300 6.0 de 4.4 ab 110 1.9 a 4.1 ab Nugget 1200 17.7 fg 4.7 b 300 4.9 c 4.3 ab 110 2.6 ab 3.9 ab A-34 1200 15.9 f 5.7 bc 300 5.7 cd 4.2 ab 110 2.3 a 4.0 ab Pennlawn 1200 18.0 gh 4.3 ab 300 6.0 de 3.2 a 110 2.7 ab 3.0 a Wintergreen 1200 17.6 fgh 4.1 ab 300 4.8 c 3.1 a 110 2.8 ab 2.9 a *Means within columns with common letters are not significantly different at the 5% level by the Duncan's Multiple Range Test. 54 Table 6. The effect of three light intensities on root res- piration rates measured with washed roots in six cool season turfgrasses after 8 weeks of growth at preconditioning light intensities. Light Cultivar Radiation Root respiration DE M‘zisec‘I' -mgC02 gm'I'hr-l- Merion 1200 5.1 ab 300 5.8 ab 110 5.3 ab Park 1200 4.3 ab 300 6.0 ab 110 6.5 ab Nugget 1200 4.6 ab 300 6.0 ab 110 7.0 ab A-34 1200 3.9 a 300 7.9 b 110 7.8 b Pennlawn 1200 4.9 ab 300 5.1 ab 110 8.1 b Wintergreen 1200 5.2 ab 300 8.2 b 110 8.1 b *Means within columns with common letters are not signifi- cantly different at the 5% level by the Duncan's Multiple Range Test. (A) (B) _—-——— Figure 1. The relative rate of 11'C-assimlate translocation. (A) Plants from left to right--Merion Kentucky bluegrass, Merion Kentucky bluegrass, Park Kentucky bluegrass, Park Kentucky bluegrass. (B) Radioautographs, from left to right--Merion Kentucky bluegrass 1/2 hr after 1 C-labelling, Merion Kentucky bluegrass 2 hr after 14C-labelling, Park Kentucky bluegrass 1/2 hr after 1"C-labelling, and Park Kentucky bluegrass 2 hr after 1"C- labelling. (A) (B) 56 -—-—'—'—"‘" Figure 2. The relative rate of 14C-assimilate translocation. (A) Plants, from left to right--Nugget Kentucky bluegrass, Nugget Kentucky bluegrass, A-34 Kentucky bluegrass, A-34 Kentucky bluegrass. (B) Radioautograph, from left to right--Nugget Kentucky blue- grass, 1/2 hr after 14C-labelling, Nugget Kentucky bluegrass 2 hr after 14C-labelling, A-34 Kentucky bluegrass 1/2 hr after 14C-labelling, and A-34 Kentucky bluegrass 2 hr after 14C- labelling. (A) (B) 57 Figure 3. The relative ratecfiEIAC-assimilate translocation. (A) Plants, from left to right--Pennlawn red fescue, Pennlawn red fescue, Wintergreen chewings fescue, Wintergreen chewings fescue. (B) Radioautographs, from left to right--Penn1awn red fescue 1/2 hr after 1 C-labelling, Pennlawn red fescue 2 hr after 14C-labelling, Wintergreen chewings fescue 1/2 hr after 14C- labelling, and Wintergreen chewings fescue 2 hr after 14C- labelling. CONCLUSIONS Lower cutting heights and increased mowing frequencies resulted in reduced root production, decreased shoot growth, increased net photo- synthesis, and increased dark respiration. High percent incorporation of 14C—photosynthate occurred in the root and stem fractions and lower accumulation of percent labelled photo- synthate resulted in the leaf fraction as mowing frequencies increased. High dark respiration rates were associated with a wounding respiration and accelerated lateral shoot growth. The effect of mowing on accelerated dark respiration and defoliation of leaf area are suggested as the major contributing factors asso- ciated with mowing stress. Lateral shoot development occurred after the third leaf stage in Kentucky bluegrass and after the fifth leaf stage in red fescue. Tiller develOpment preceded rhizome initiation in red fescue; whereas, tillers and rhizomes were not initiated preferentially to one another in Kentucky bluegrass. Tillering occurred in the axils of leaves below fully expanded leaves in both species. High photosynthetic rates, greater percent of leaf dry weight and high dark respiration rates occurred during the initial weeks after seedling emergence. The develOpmental and physiological changes associated with seedling growth may signify critical changes in plant metabolism. 58 59 10. All cultivars investigated at reduced light intensities responded similarly or lacked definite trends in terms of net photosynthesis, dark respiration, root respiration and relative rate of 14C-photo- synthate translocation. ll. Pennlawn red fescue and Wintergreen chewings fescue tended to show a decreasing trend in dark respiration as light intensity was lowered. 12. The incorporation of 14C—photosynthate was high in the stem fractions in Nugget and A-34 Kentucky bluegrass at the lowest light intensity. This trend may be associated with a shade adaptive mechanism within Kentucky bluegrasses. The results of this investigation revealed new information concerning turf growth and develOpment, mowing stress, and shade tolerance. Understanding these aspects of turf culture allows the turf professional to implement and adjust cultural practices to improve the level of turfgrass quality. Further investigations into these areas of research will promote the understanding and general knowledge associated with turfgrass management. Further investigations may include: a) elucidation of wounding as a contributing factor in mowing stress; b) investigation of various environ- mental and nutritional factors associated with lateral shoot development; c) the significance of the shift in 14C-photosynthate from the leaves to stems during seedling growth; d) investigation of the trend in reduced dark respiration as light intensities decreased in Pennlawn red fescue and Winter- green chewings fescue; and 3) the relationship of high 14C-photosynthate incorporation into the stem fraction in Nugget and A-34 Kentucky bluegrass grown under reduced light intensities to a possible shade adaptive mechanism. LIST OF REFERENCES 10. 11. LIST OF REFERENCES Adegbola, A. A. and C. M. McKell. 1966. Effect of nitrogen ferti- lization on the carbohydrate content of coastal bermudagrass (Cynodon dactylon L. Pers.). Agron. J. 58:60-64. Alberda, T. 1957. The effects of cutting, light intensity, and night temperature on growth and soluble carbohydrate content of Lolium perenne L. Plant and Soil. 8:199-230. Alburquerque, H. E. 1967. Leaf area, and age, and carbohydrate reserves in the regrowth of tall fescue (Festuca arundinacea Schreb.) tillers. Ph.D. Thesis. Virginia Polytechnic Institute. pp. 1-278. Alexander, C. W. and K. E. McCloud. 1962. C02 uptake (net photo- synthesis) as influenced by light intensity of isolated bermuda- grass leaves contrasted to that of swards under various clipping regimes. Crop Sci. 2:132-135. Areda, H., R. E. Blaser and R. H. Brown. 1966. Tillering and car- bohydrate contents of orchardgrass as influenced by environmental factors. Crop Sci. 6:139-143. Asahi, T., Y. Honda and I. Uritani. 1966. Increase of mitochon- drial content in sweet potato after wounding. Arch. Biochem. Biophys. 113:498-99. 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. 1-658. Bjorkman, 0. 1968. Further studies on differentiation of photo— synthetic properties in sun and shade ecotypes of Solidago virgaurea. Physiol. Plant. 21:1-10. Bjorkman, 0. and P. Holmgren. 1963. Adaptability of the photo— synthetic apparatus to light intensity in ecotypes from exposed and shaded habitats. Physiol. Plant. 16:889-914. Bjorkman, O. and P. Holmgren. 1966. Photosynthetic adaptation to light intensity in plants native to shaded and exposed habitats. Physiol. Plant. 19:854—859. 60 12. 13. 14. 15. 16. 17. l8. 19. 20. 21. 22. 23. 24. 25. 26. 61 Bjorkman, 0., M. M. Ludlow, and P. A. Morrow. 1972. Photosynthe- tic 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. p. 94-102. Bohning, R. H. and C. A. Burnside. 1956. The effect of light intensity on rate of apparent photosynthesis in leaves of sun and shade plants. Am. J. Bot. 43:557-561. Brady, H. A. 1969. Light intensity and absorption and transloca- tion of 2,4,5-T by woody plants. Weed Sci. 17:320-322. Brown, M. E. 1943. Seasonal variatiOns in the growth and chemical composition of Kentucky bluegrass. Missouri Ag. Expt. Station, Research Bulletin No. 360. pp. 5-56. 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. Butcher, H. C. 1965. The kinetics of carbon-14 translocation in sugar beets: an effect of illumination. Dissertation Abstr. 25:7350. Carpenter, S. L. 1971. Developmental changes in assimilation and translocation of photosynthate in Black Walnut (Juglans nigra L.) and Honey-locust (Gleditisia triacanthus L.) seedlings. Ph.D. Thesis. Michigan State University. pp. 1—85. Crafts, A. S. and C. E. Crisp. 1971. Phloem transport in plants. W. H. Freeman and Co., San Francisco, Calif. pp. 1-357. DeFrance, J. A. and J. A. Simmons. 1951. Relative period of emer- gence and initial growth of turfgrasses and their adaptability under field conditions. Proc. of Am. Soc. for Hort Sci. 57:439-442. Dodd, J. D. and H. H. Hopkins. 1958. Yield and carbohydrate of blue grama grass as affected by clipping. Transactions of Kansas Academy of Science. 61:(3):280-287. Everson, A. C. 1966. Effects of frequent clipping at different stubble heights on western wheatgrass (Agropyron smithii Rybd.). Agron. J. 58:(l):33-35. Harrison, C. M. 1931. Effect of cutting and fertilizater applica- tion on grass development. Plant Physiol. 6:669-684. Hartt, C. E. 1965. Light translocation of 14C in detached blades of sugar cane. Plant Physiol. 40:774-781. Hartt, C. E. 1966. Translocation in colored light. Plant Physiol. 41:369-372. Hoagland, D. R. and D. I. Arnon. 1950. The water culture method for growing plants without soil. Calif. Agr. Exp. Sta. Cir. 347. p. 32. 27. 28. 29. 30. 31. 32. 33. 34. 35. I36. I37. 383. I39. 40. 62 Hodgkinson, K. K. and J. A. Veale. 1966. The distribution of photosynthate within lucerne as influenced by illumination. Aust. J. Biol. Sci. 19:15-21. Hulme, A. C., M. H. C. Rhodes, T. Galliar, and L. S. C. Wooltorton. 1968. Metabolic changes in excised fruit. IV. Changes occurring in discs of appls peel during the development of the respiration climacteric. Plant Physiol. 43:1154-61. Imaskli, J. M., A. Uchigamo and J. Uritani. 1968. Effect of ethy- lene on the inductive increase in metabolic activities in sliced sweet potato roots. Agr. Biol. Chem. 37:387—89. Karnok, K. J. 1974. Physiological characteristics of heat tolerance and susceptible creeping bentgrass (Agrostis palustris Huds.). M.S. Thesis. U. of Ariz. pp. 25. Kortschak, H. P. and A. Forkes. 1969. The effect of shade and age on the photosynthesis rate of sugar cane. In: Metzner, H. (ed.): Progress in Photosynthetic Research. Vol. 1. pp. 383-387. Madison, J. H. 1960. The mowing of turfgrass. I. The effect of season interval and height of mowing on the growth of Seaside bentgrass turf. Agron. J. 52:449-456. Madison, J. H. 1962. The mowing of turfgrass. II. Response of three species of grass. Agron. J. 54:250-252. Madison, J. H. 1962. Mowing of turfgrass. III. The effect of rest on Seaside bentgrass turf mowed daily. Agron. J. 54:252-253. Madison, J. H. 1962. Turfgrass ecology. Effects of mowing, irri- gation, and nitrogen treatments of Agrostis palustris Huds., "Seaside" and Agrostis tenuis Sibth., "Highland” on population, yield, rooting, and cover. Agron. J. 54:407-412. Madison, J. H. and R. M. Hagan. 1962. Extraction of soil moisture by Merion bluegrass (Poa pratensis L. 'Merion') turf, as affected by irrigation frequency, mowing height, and other cultural oper- ations. Agron. J. 54:157-160. Maggs, D. H. 1963. The reduction in growth of apple trees brought about by fruiting. J. Hort. Sci. 38:119-122. McCarty, E. C. and R. Price. 1942. Growth and carbohydrate content of important mountain forage plants in central Utah affected by clipping and grazing. U.S.D.A. Tech. Bulletin No. 818. pp. 1-51. McGlasson, W. B. and H. K. Pratt. 1964. Effects of wounding on res- piration and ethylene production on cantaloupe fruit tissue. Plant Physiol. 39:128-132. Meyer, S. B., D. B. Anderson, R. H. Bohning, and D. G. Fratianne. 1973. Introduction to Plant Physiology. D. Van Nostrand Co., New York, New york. pp. 235. ' 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 63 Mitchell, K. J. 1953. Influence of light and temperature on the growth of ryegrass (Lolium spp.). II. The control of lateral bud development. Physiol. Plant. 6:425-442. Mitchell, K. J. 1955. Growth of pasture species. 11. Perennial ryegrass (Lolium perenne), cocksfoot (Dactylis glomerata), and paspalum (Paspalum dilatatum). New Zealand J. Sci. & Tech. Sec. A. 37(1):8-26. Mitchell, K. J. and S. T. J. Coles. 1955. Effects of defoliation and shading on short-rotation ryegrass. New Zealand J. Sci. & Tech. Sec. A. 36:(6):586-604. Nelson, C. D. 1963. Effect of climate on the distribution and translocation of assimilates. In: "Environmental Control of Plant Growth," ed. by L. T. Evans, Academic Press, New York, pp. 149-173. Nelson, C. D. 1964. The production and translocation of photosyn- thate C14 in conifers. In: "The Formation of Wood in Forest Trees," ed. by M. H. Zimmermann, Academic Press, New York. pp. 243-257. Nelson, C. D. and E. C. Humphries. 1957. Uptake and translocation of C-14 labelled sugars applied to the primary leaves of soybean seedlings. Can. J. Bot. 35:339-347. Nyahoza, J. L. 1973. The interrelationship between tillers and rhizomes of Poa pratensis L. - an autoradiographic study. Weed Sci. 13:304-309. Patel, A. S. and J. P. Cooper. 1961. The influence of several changes in light energy on leaf and tiller development in rye- grass, timothy and meadow fescue. Jour. of the British Grass- land Soc. 16:299-308. Quinland, J. D. and G. R. Sagar. 1969. An autoradiographic study of the movement of 1 -labelled assimilates in the developing wheat plant. Weed Res. 2:264—273. Rhohrbaugh, L. M. and E. L. Rice. 1949. Effect of application of sugar on the translocation of sodium 2,4-dichlorophenoxy acetate by bean plants in the dark. Bot. Gaz. 110:85-89. Sakano, K. and T. Asahi. 1971. Biochemical studies on the biogene- sis of mitochondria in wounded sweet potato root tissues. 1, Time course analysis of increase in mitochondrial enzymes. Plant and Cell Physiology. 12:417-426. Shen, G. M. 1960. Translocation and distribution of assimilates from the leaves of rice plants during its various developing periods-~experiments with radioactive carbon (C1 ). Acta Agric. Sinica 11:30-40. (Biol. Abst. 35:4648-4649. 1960) 53. 54. 55. 56. 57. 58. 59. 60. 61. 64 Smith, D. 1968, Carbohydrates in grasses. IV. Influence of temperature on the sugar and fructosan composition of timothy plant parts at anthesis. Crop Sci. 8:331-334. Soper, K. and K. J. Mitchell. 1956. The developmental anatomy of perennial ryegrass (Lolium perenne L.). New Zealand J. Sci. & Tech. Sec. A. 37:484—504. Thorne, J. H. and R. Koller. 1974. Influence of assimilate demand on photosynthesis, diffusive resistances, translocation and carbohydrate levels of soybean leaves. Plant Physiol. 54:201-207. Thrower, S. L. 1962. Translocation of labelled assimilates in soybean II. The pattern of translocation in intact and defoliated plants. Aust. J. Biol. Sci. 15:629-649. Wilkinson, J. F. and J. B. Beard. 1974. Morphological responses of Poa pratensis and Festuca rubra to reduced light intensity. p. 231—240. In: "Proceedings of the Second International Turfgrass Research Conference." ed. by E. C. Roberts. Am. Soc. of Agron., Madison, Wis. Wilkinson, J. F., J. B. Beard, and J. V. Krans. 1975. Photosyn- thetic-respiratory resonses of 'Merion' Kentucky bluegrass and 'Pennlawn' red fescue at reduced light intensities. Crop Sci. 15:165-168. Wilson, D. and J. R. COOper. 1969. Apparent photosynthesis and leaf character in relation to leaf position and age, among contrasting Lolium genotypes. New Phytol. 68:645-655. Vaartnou, H. 1967. Responses of five genotypes of Agrostis L. to variations in environment. Ph.D. Thesis. Oregon State University. pp. 1-149. Vanden Driessche, R. and P. F. Wareing. 1966. Dry-matter pro- duction and photosynthesis in pine seedling. Ann Bot. 30: 673-682. "I111111111111111111115