131 553 “ tho—“f“‘f v. :r-A‘ .. LIBRARY Michigan State University "€915 This is to certify that the thesis entitled THE EFFECT OF HIGH CROWN AND ROOT TEMPERATURE ON SHOOT AND ROOT GROWTH OF KENTUCKY BLUEGRASS (Poa pratensis L.) presented by Rafael Angel Yajure has been accepted towards fulfillment of the requirements for Master degreein Crop Science Dr. John E. Kaufmann DatQfiM Z, I? 81) 0-7639 L“. L‘- ué ‘7' q fl-‘i\\\\ { affine: ~- ‘ ; ‘muw ' . . . OVERDUE FINES: 25¢ per 60 per its Immune LIBRARY MTERIAL§: Place in book return to new charge from circulation recon THE EFFECT OF HIGH CRONN AND ROOT TEMPERATURE ON SHOOT AND ROOT GROWTH OF KENTUCKY BLUEGRASS (POA PRATENSIS L.) by Rafael A. Yajure A THESIS Submitted to Michigan State University in partial fulfillment of the requirement for MASTER OF SCIENCE DEPARTMENT OF CROP AND SOIL SCIENCE l980 DEDICATION This thesis is dedicated to my parents and those that built a family, Nicomedez, Agrispina, Equenio Lola, Rosa, Isabel, Isabel Maria, Juan, Claudia, Pausolina, Carmen. To those gone for ever. To those that I will never ignore, Juan, Jorge, Aristides, Antero and Santos. To my brothers. Also I wish to dedicate this thesis to my friends Federico, Marcos and Catalina. ii ACKNOWLEDGEMENTS I wish to express my gratitude to Dr. J. E. Kaufmann for his interest, advice and wise guidance during my graduate studies, as well as for his encouragement to affront the difficulties in pursuing my professional and personal goals. Thanks are also extended to the faculty for its time, advice, and assistance, particularly those who served on the guidance com- mittee: Drs. P. E. Rieke and G.R. Safir. In addition, the author wishes to express a special thanks to the sponsor, Universidad Ezequiel Zamora (Venezuela) and to the university authorities, for the support and the opportunity to broaden myself and better serve my country. TABLE OF CONTENTS List of Tables . LiSt of Figures. INTRODUCTION. LITERATURE REVIEW . . . Effect of temperature on shoot growth The effect of temperature on tillering . The effect of temperature on rhizome and root growth Root distribution as affected by environmental stresses . . Surface soil temperature effects on shoot and root growth. MATERIAL AND METHODS . . . . Plant material establishment procedure . Method for Temperature Treatment of Plants . Leaf temperature control. . Crowns temperature control chambers . Root temperature control. . Nutrient Solution Misting System Cool and Hot Water Circulation System. Source of cool and hot water Growth Chamber Procedure . Growth Response Measurements. RESULTS . . . The Effect of Crown and Root Temperature on .Dry Weight Production. . . . . . . . . Clippings. . Stubble and Crowns. Total Shoot . . Rhizome and Total Root . . . Total Dry Weight of the Plant . Crown Region Root . . Rooting Chamber Root Dry Weight Root/Shoot Ratios . . The Effect of Crown and Root Temperature on Tiller, Rhizomes and Total Number of Innovations. . . . The Effect of Crown and Root Temperature on Leaf Extension Rate . . . . . . . . iv Page vi Page DISCUSSION. . . . . . . . . . . . . . . . . 49 CONCLUSION. . . . . . . . . . . . . . . . . 6l LITERATURE CITED. . . . . . . . . . . . . . . 63 APPENDIX . . . . . . . . . . . . . . . . . 69 Table LIST OF TABLES The effect of crown and root temperature on clip- ping, stubble, crown, rhizome and root dry weight of Merion Kentucky bluegrass grown in a 22C growth chamber for 5 weeks. . . . . . The effect Of crown and root temperature on root/ shoot ratios of Merion Kentucky bluegrass grown in a 22C growth chamber for 5 weeks . . . . The effect of crown and root temperature on the number of innovations per plant of Merion Kentucky bluegrass grown in a 22C growth chamber for 5 weeks The effect of crown and root temperature on leaf extension rate of Merion Kentucky bluegrass growth in a 22C growth chamber for 5 weeks . . vi Page 37 43 45 48 Figure LIST OF FIGURES Crown temperature control chamber (CTCC), Diagram and dimensions of the chamber. . . . . Tiller placement in the crown temperature control chamber and harvesting dimensions for different plant components . . . . Illustrations Of the system designed to indepen- dently control crown and root temperatures of Kentucky bluegrass . . . . . . . The effect of crown-root temperatures on weekly clipping yield of Merion Kentucky bluegrass . The effect of crown-root temperatures on crown- region root (2-0 cm range) and rooting chamber root dry weights in Merion Kentucky bluegrass Page 22 24 26 35 4O INTRODUCTION Temperature and water influence global distribution Of plants. Within a region seasonal fluctuations of these environmental para- meters often determine sites Of adaptation. Grasses, such as Ken- tucky bluegrass, that are adapted to temperate areas are subjected to periods of drought, and to temperatures above the optimum for Sustained growth during the summer season. Descriptive terms such as growth inhibition, growth stoppage, mid—summer depression of growth and dormancy have been used to describe the effects of high temperatures on turfgrass growth in experiments where water is sup- plied as needed. Controversy has arisen in determining the site of tempera- ture perception. A widely accepted hypothesis suggest roots rather than shoots are the perception organ. However, it has been long recognized that different parts of the plant may respond differently to temperature. Few experiments have been designed to study the effect of localized temperature on different plant parts. In these experiments growth responses to temperature have been limited to parameters related to leaf growth. The Objectives Of this investigation were to determine (a) the site of heat stress perception of Merion Kentucky bluegrass, and (b) how growth of the whole plant including shoots, crowns, rhi- zomes and roots is affected by independently controlled leaf, crown l and root temperatures when light, water and nutrients are held con— stant. The results obtained should assist in understanding whole plant growth responses of grasses grown under heat stress conditions. LITERATURE REVIEW Effect of temperature on shoot growth The Optimum temperature for maximum shoot growth does not necessarily mean the optimum temperature for maximum turfgrass qua- lity. Cool season turngrasses such as Kentucky bluegrass (Egg pratensis L.) can sustain high levels of shoot growth under a wide range Of temperatures (Brown, T939; Harrison, T934). Optimum temperature for shoot growth of Kentucky bluegrass and other cool season grasses has been reported to be in the range of 6D (T5.5 C) to 75 F (23.8 C) by Baker and Jung (l968), Brown (T943), Darrow (T939), and Harrison (T934). Optimum temperature ranges have been shown to be based on shoot growth rates over an extended period of time by Alberda (T957), McKelT et al. (T969), and Watschke et al. (T972). These authors have reported that shoot growth decreases as temperature is increased or decreased from the optimum. However, for short time periods shoot growth has been found to be more rapid at slightly above Optimum temperatures (Alberda, T957). Similar findings have been reported in other cool season grasses such as perennial ryegrass (Lolium perenee L.) by Mitchell (T955), Canada bluegrass (Poa compresa L.) by Hiesey (T953), creep- ing bentgrass (Agnostis palustris Huds.) by Duff (T967), and annual bluegrass (Egg annua L.) by Hiesey (T953). 3 Watschke et al (T972) evaluated ten Kentucky bluegrass cul- tivars grown for two weeks at 23 C day l5 C night after which temp- erature was changed to 35 C day 25 C night. All cultivars increased in foliar production during the first week at high temperature. However, the decrease in clipping yields were dramatic during the 2nd and 3rd weeks at high temperature. Only four of the six grasses with highest yields during the 4th week of high temperature also had the slightest decline in foliar growth at 35 to 25 C. In another study Youngner and Nudge (T968) measured the growth of Merion, Fylking and Newport Kentucky bluegrass cultivars when influenced by temperature. The plants were grown at day-night temperature regimes of 27-2T, 27-16; T8-l2 and T6-7 C. Shoot dry matter production of Merion Kentucky bluegrass was greater than for the other two cultivars. Shoot growth was greatest at the warmer temperature and decreased with decreasing temperature. Sullivan and Sprague (T949) working with Perennial ryegrass found higher dry matter production of shoots when the day-night temperature was 2T.T-T5.6 C and the lowest at 32.2-26.7 C. Robson (T973) worked with Tall fescue (Festuca arundinacea) subjected to a constant night temperature of 20 C while day tempera- ture was varied from T0 to 30 C. Likewise, day temperature was held constant at 20 C while night temperatures were varied from T0 to 30 C thus maintaining a constant mean temperature of 20 C in five regimes, 30/l0, 25/T5, 20/20, l5/25 and l0/30 C. In this study leaf lamina length and area, sheath length, rate of leaf growth, leaf area ratio, specific leaf area, leaf weight ratio, unit leaf rate, relative rate Of leaf area and relative growth rate were found to achieve maximum values in the 25/25 C regime and were more affected by the day temperature than by that Of the night tempera- ture. He concludes that when the day temperature was Optimal at 25 C, or slightly sub-optimal at 20 C, the Optimum night tempera- ture was one equal to that of the day. When the day temperature was markedly subOptimal at TD or l5 C a higher night temperature favored growth. Only when the day temperature was supraoptimal (above the Optimum) at 30 C was a lower night temperature beneficial. These results did not agree with the concept Of thermoperiodicity or the response Of plants to rhythmic fluctuations in temperature. However, certain turfgrass species have been reported to exhibit a thermoperiodic response according to other authors pre- viously cited, especially Brown (l939) and Hiesey (T953) when researching Kentucky bluegrass. The findings of McKell et al., (T969) and Watschke, Schmidt and Blaser (T970), also support the concept Of thermoperiodicity Of this specie. Baker and Jung (T968) studied the effect of day (from l8.3 to 34.8 C in increasing 3.3 C intervals), and night temperatures (from T.8 to l8.3 C in increasing 3.3 C intervals) on the dry weight of top growth Of Kentucky bluegrass, orchardgrass (Dactylis glomerata L.) and bromegrass (Bromus inermes Leyess). Bluegrass appeared to be very sensitive to night temperatures when the day temperature was l8.3 C. When the day temperature was 2T.6 or 24.9 C more variations in yields were observed due to night temperatures. A night temperature of 8.4 C was reported to be more favorable for orchardgrass and bluegrass when the day temperature was 28.2 or 3l.5 C. At the 34.8 C day temperature, none Of the night tempera- tures appeared to favor top growth Of bluegrass. This regime yielded the lowest top growth in all the species. In general, growth of Kentucky bluegrass at T5 C is described as having profuse, long, succulent, bushy shoots while at 35 C as being short, less succulent, rigid with limited production Of leaves and reduced bud initiation (Aldous, T978; Darrow, T939). The effect Of temperature on tillering A tiller is a primary lateral shoot that arises intra or extra-vaginally from the stem base with unlimited elongation. More specifically a tiller forms from vegetative bud in the axil of leaf sheaths (Beard, T973). Tillers are an important component Of turf grass density. Tillers have also been reported to have an Optimum tempera- ture range similar to that Of the shoot (Alberda, T957; Brown, T943; Cooper, T957; and McKell et al., T969) or slightly lower than the Optimum for shoot growth (Alberda, T965; Duff, T967). These authors have reported the number of tillers to be affected prOportionally as temperature is increased or decreased from the Optimum. Peterson and Loomis (T948) exposed Kentucky bluegrass plants to ll, T5, and T9 hrs. of light and cool temperatures of 55.8 F(l3.2C) to 6T.2 F (T6.2), while warm temperatures were 65.4 F (l8.6 C) to 74.7 F (23.7 C). It was concluded that tiller number was affected more by photoperiod than by temperature. Slightly higher number Of tillers were found at the ll hr. light period and cool tempera- ture regime. Tiller number appeared to be independent of temperature. A similar conclusion was reached by Baker and Jung (T968). Mitchell (l953a) reported the quantity of light to be a chief factor determining tiller number in perennial ryegrass. The number of tillers were nearly quadrupled when light was raised from 700 fc to 2,000 fc (the lowest and highest light intensities used). However, the conclusion was that low light levels, high temperature (26.6 C) or both tend to inhibit bud develOpment from the basal node. In a subsequent study the same author (l953b) stated that inhibition Of lateral bud development was induced by either shade, reduction of photoperiod, high temperature or partial defoliation. Environmental conditions in the second study was similar to those in the first. Using a broader range of temperatures (7.2 to 35 C), Mitchell (T956) determined in a later study that l8.3 to 2l.l C is the Opti- mum range for total shoot growth of perennial ryegrass, cocksfoot (Dactylis glomerata L.) and browntop (Agrostis tenuis Sibth.). However, relatively little change in the growth rate Of an indivi- dual tiller was noticed over the temperature range when compared to total shoot growth. The percentage increase per day in tiller number Of perennial ryegrass peaked at 58 F (l4.4 C) and the lowest percentage was found at 95 F (35 C). Youngner and Nudge (l968) expressed the density of Merion Kentucky bluegrass as the number Of tillers per pot and was found to be the highest at the highest temperature and decreased with decreasing temperature. The Optimum temperature was found to be different among Merion, Fylking and Newport. Robson (l973) found the duration of leaf growth Of tall fescue (which determines the delay of a successor leaf) and the number of days between the appearance of successive leaves was reduced by rais- ing either the day or the night temperature from T0 to 30 C. High temperature accelerated the leaf appearance rate. Because a tiller develops from the vegetative buds in the axil of the leaf sheath the appearance rate of tillers was also accelerated. However, raising day or night temperatures depressed the tiller number. All the plants used in this study were at the same stage of growth, and had three fully expanded leaves on the stem. The only difference was presence or absence Of a tiller in the axil of the leaf. Robson (l973) con- cluded that if the plant had been compared by chronological, rather than physiological age, a greater rate of tillering at high tempera- ture might have been expected rather than the reduced rate he found for older plants in a previous study (Robson, l969). Using radiactive labeled organic compounds, Williams (T964), Marshall and Sagar (l965), and Forde (l966) have traced the fate Of assimilates in Phleum pratense L., Lolium multiflorum Lam., and perennial ryegrass, respectively. They were able to show that a fully developed tiller was independent of its parent and sister tillers for carbohydrate supply. However, under adverse conditions (defoliation or darkening) 14C- assimilates were imported from parts of the plant not affected by the treatment. It has also been reported by Fiveland, Erikson and Seely (T972) for Agropyron repens L. that assimilates were translocated along the rhizome only after defoliation of the main plant. In an attempt to clarify the relationship between the tiller and the horizontal and erect rhizome, Nyahoza, Marshall and Sagar (T973) supplied 14C02 to the main shoot Of Kentucky bluegrass plants and the distribution of 14C assimilates was traced by autoradiography. It was found that although the primary tillers and rhizome tillers Of the intact plant appeared to be physiologically independent, the entire tiller-rhizome system reintegrated after defoliation, allow- ing assimilate distribution. Robson (T968) argued that when assimilates are in short supply, existing tillers are favored at the expense of new tillers. The same author in a later study (l973) found that perennial rye- grass tiller number was suppressed at high temperature (particularly between 20 and 30 C) and this effect was linked to the lowest content Of water soluble carbohydrates (WSC) at those temperatures. How- ever, whether Or not WSC decrease with increasing temperatures is doubtful in the light of new findings in this research area (Brown and Blaser, T970; Martin, T972; and Duff and Beard, T974 among others) which indicate an increase rather than a decrease of WSC with increasing temperatures. TO The effect Of temperature on rhizome and root growth A rhizome is an extravaginal, secondary lateral shoot that elongates underground. In Kentucky bluegrass a rhizome arises from nodes at the base Of the aboveground shoot and from nodes Of Older rhizomes (Beard, T973). Rhizomes and roots have been reported to have a similar Optimum range of temperature for growth being about 5 to T0 C below that for shoots (Brown, T939; Brown, T943; Darrow, T939; Harrison, T934; Sprague, T933; Stukey, l94l; and Youngner, l96l). Evans and Ely (T935) determined that rhizome development can occur almsot at any time in the year as long as soil tempera- tures are above 32 F, and that maximum growth rates occur under long day lengths, high light intensity and lower levels of nitrogen. Rhizome growth is reduced by prolonged periods of drought and heat or low temperature stress (Brown, l943; Etter, l95l; Hanson and Juska, T96l). Moser, Anderson and Miller (T968) studied rhizome initiation and development of Merion and Windsor Kentucky bluegrass. The plants were exposed to 8, l2, T6 and TB hr. photoperiods and constant temp- eratures of 0 to 2 C (cold treated) and 20 to 2T C (not cold treated). It was concluded that a cold treatment is not necessary for rhizome formation. Both initiation and elongation were favored by T6 or l8 hour photoperiod. Rhizomes are important components Of Kentucky bluegrass sur- vival and density. It has been determined that following both winter TT and summer dormancy, shoot regrowth is initiated from meristematic regions on rhizomes, and crown of shOOts (Olmsted, T942). Brown (T939) and Harrison (T934) determined that temperatures above 25 C stimulate the emergence of the growing point Of Kentucky bluegrass rhizomes above the soil. When the tip Of a rhizome is exposed to light or the lower C02 concentration of the atmosphere, horizontal growth is inhibited and the internodes adjacent to the tip turn upward. ChlorOphle is then formed in the leaf scales Of the tip (Beard, T973). It has been previously documented that the optimum tempera- ture range for root growth is 5 to l0 C below that for shoots. The range has been determined to be between 50 F (l0 C) to 65 F (l8.3 C) for species such as Kentucky bluegrass (Cooper and Calder, l962; Youngner, l96l), perennial ryegrass (Mitchell, T955), and creeping bentgrass (Beard and Daniel, T965). Youngner and Nudge (T976) found that a soil temperature of 27 C resulted in reduced root dry matter production and root length of Kentucky bluegrass compared to roots growing at l8 C sOiT tempera- ture. At 32 C there appeared to be no live functioning roots although crowns and leaves were still alive. Defoliation enhanced high temp- erature suppression of both top and root growth. Beard and Daniel (T965) found that the growth rate Of indi- vidual roots and total root production of creeping bentgrass (Agrostis palustris Huds.) was reduced when the plants were exposed to 90 F (32.2 C). Cessation of growth of an individual root appeared to be more rapid as temperatures increased from 60 (l5.5 C) to 90 F T2 (32.2 C). However the rate of root growth on a per day basis was similar in the 60 F (T5.5 C) to 80 F (26.4 C) range. In another study the authors (Beard and Daniel, T966) investigated creeping bentgrass grown in irrigated field conditions and found root temp- eratures at 6 in. (T5 cm) depth highly correlated with root growth. The greatest variation in extremes of temperature occurred at l in. (2.54 cm) aboveground. Maximum temperatures of llO F (43.3 C) were recorded at the soil surface in mid-August. NO new root growth was Observed from June to November except for two periods when the maxi- mum daily temperature dropped sharply. It was suggested that lower temperatures either initiated root elongation or were required for elongation to occur. In general, roots growing in the optimum range of tempera- ture are described as white, fleshy, multibranched and thick (Beard and Daniel, T965; Darrow, T939; Stukey, T942). These authors also described root growing at temperatures above the Optimum as fila- mentous Spindly, inactive and brown to dark brown in color. Root distribution as affected by environmental stresses Another feature of root growth under environmental stress is the ability of the root system to show a compensatory growth. If the growth of one part of the root system is reduced or inhibited, growth of other roots in more favorable conditions is frequently enhanced (Russel, l977). Temperature effects on compensatory growth Of barley (Hordeum vulgare) roots was examined by Crossett et al. (T975). The root l3 system of barley plants was divided into two parts, with half of the root system maintained at all combinations of 20 C and TO C. Air temperature was l5 C throughout and the nutrient supply was constant. The growth Of one half Of the root system maintained at 20 C (which is a more favorable temperature for root growth) was greater when the temperature of the other half was at To C and the growth of one half of the root system at T0 C was less when the temperature of the other half was at 20 C. A similar compensatory growth capability Of the root system has also been reported to occur due to uneven distribution Of water in the soil layers, where a growth restriction in part Of the root system may lead to increased growth of roots in a moist environment (Ellis et al., T977; Klepper et al, T973). In the case Of nutrients, the effects are more striking. Drew (T975) and Drew and Saker (T975), examined the effects of localized supply Of phosphate, nitrate, ammonium and potassium on the growth Of the seminal root system and the shoots of barley. When seminal roots (axes) were exposed to a localized high concen- tration of phosphate, initiation and extension Of first and second laterals was greater than those receiving very low concentration of phosphate. This resulted in considerable modification Of root form, with only a small loss in shoot growth compared with control plants receiving an ample nutrient supply to all parts of the root system. Similar responses were Observed with nitrogen but not with potassium where a localized supply caused branching on all remaining parts. l4 Surface soil temperature effects on shoot and root growth Evidence concerning the relative importance Of soil and air temperatures within the Graminae is conflicting. Allmaras, Burrows and Larson (T964) concluded that root temperature was the main factor controlling shoot growth of corn (Zea may; L.). Sato and Ito (T969) analyzed growth responses to air and soil temperatures of orchardgrass and perennial ryegrass. It was concluded from these studies that soil temperatures determined growth in terms Of plant height, leaf emergence, tiller number, leaf area and dry matter production when the air temperature was either lower or higher than the Optimum. Recently Aldous and Kaufmann (T979) reported supra-optimal temperature to be perceived in the roots. Merion and Nugget Kentucky bluegrass were exposed to air temperatures increased from 22 to 38 in 4 C increments every 2 weeks. The effects Of root zone temperature were compared in two conditions, where the root temperatures were controlled at 22 C (CRT) and non-controlled (NRT) where root tempera- ture equilibrated with air temperatures. Though shoot dry matter pro- duction was reduced at high temperature (30 to 34 C) significantly higher yields were achieved at CRT when compared to the NRT in both cultivars. 0n the other hand, Volden and Blackman (l973) found the rela- tive growth rate, the rate of increase in leaf area, and the net assi- milation rate of corn plants were positively dependent on both radia- tion and mean air temperature. In a recent study Younger and Nudge (T976) found little difference in shoot growth rate of Merion Kentucky l5 bluegrass at soil temperatures of T3, T8 and 27 C but root length was impaired at 27 C. I In early work Brown (l939) suggested soil temperatures near the surface, rather than air temperatures, were the major temp- erature regulator of growth. During the summer season temperate plants are exposed to extreme temperatures. Beard and Daniel (T966) reported maximum temperatures of ll0 F (43.3 C) at the soil surface in mid-August, in a creeping bentgrass field. The thermal microclimate of a perennial ryegrass sward was measured in order to study its relationship with crop growth (Peacock, T975a). The sward was cut at 5 cm and 4 days later on a bright sunny day (May) and with a leaf area index of 0.3, it showed a maximum diurnal temperature of 34 C when measured at 2.5 cm above the soil surface. However, an uncut 55 cm sward, with a leaf index area Of 5.6, showed maximum diurnal variation in air tempera- ture at 30 cm where most radiation was intercepted. Daily mean temperature was found highly correlated to leaf extension. The effect of localized temperatures on the stem apex (crown) Of several crop plants has been reported. Schwarz (l972) studied the effect of temperature on tomato seedlings when the crown was exposed to 38 C (warm) and 7 C (cool) compared to control plant exposed to 25 C. The plants were grown in nutrient solution with temperature held constant at l8 C. Greenhouse day air temperatures varied from 22 C to 26 C and from T6 C to 20 C at night. The tempera- ture of the crown of the plants was controlled by a stream of warm or l6 cool air. Cooling the root crown area to 7 C resulted in increased root weight while shoot weight was not markedly influenced during day time hours. When the crown area roots were exposed to high temperature (38 C) shoot growth was greatly reduced while root weight was only slightly influenced. However similar root crown temperatures (6 C and 35 C) during day and night hours resulted in decreased shoot and root weights. The author suggested that high temperature effects on crowns could reduce or alter translocation of water, nutrients, hormones and assimilates. Watts (l972) investigated the independent effect of root, apical meristem and shoot temperature on the rate of leaf extension in corn (ZSE.EEX§ L.) seedlings. In this case high temperature of the apical meristem was controlled with a heating collar placed around the crown of the plants. Low temperature was controlled by passing chilled water through the collar. Roots were grown in either nutrient solution or John Innes NO. l compost and the tempera- ture was controlled by a water bath. When the temperature Of the apical meristem and region Of cell expansion at the base Of the leaf was kept at 25 C, increases of leaf extension in response to changes of root and shoot tempera- ture were less pronounced. When the temperature Of the meristematic region was changed by increments of 5 or l0 C over a range from 0 to 40 C, and the root and shoot temperature were kept at 25 C, rapid increases in rate of leaf extension were recorded, but the rate declined rapidly between 35 and 40 C. It was concluded that the rate T7 of leaf extension were controlled at root-zone temperatures Of 5 to 35 C by heating or cooling Of the meristematic region. Peacock (l975b) using a similar technique to those used by Watts (l972) exposed the crown region Of perennial ryegrass seedlings from 2 to 40 C independent of the temperature to which the rest Of the plant was subjected (5 or l5 C) in a growth room experiment. The lowest stem apex temperature (2 C) in the 5 C room was achieved by circulating ethylene glycol solution around the collar but it was not possible to maintain this low temperature in the T5 C room. Results were presented in terms of a fitted by eye curve which showed the relationship between leaf extension and temperatures in the region Of the stem apex. A maximum rate of leaf expansion of about 52 mm per day was achieved at 5 C air and at 28 C apical meristem temperatures. This maximum rate was also achieved at l5 C air and 32 C apical meristem temperatures. The rate of leaf expansion dropped, although not significantly, from 52 mm to 42 mm when the apical meristem temperature was increased to a range between 34 to 38 C or both air temperatures. Neverthe- less, the author concluded that the rate of leaf expansion was dependent on stem apex temperature rather than air temperature. Peacock (l975b) designed a similar experiment in field con- dition using heating cables installed below the main rooting zone at a depth of TS cm by which it was possible to raise the tempera- ture at the soil surface by at least 5 C increments. Response curves of leaf extension plotted against mean temperature in both the control and heated plots showed a closer correspondence with l8 soil surface temperatures than 5 or T0 cm above the soil surface. This was the case when measurements were done for the spring and autumn season. During the summer period the rate of leaf expansion was affected by water stress even though the crop was irrigated, thus the data was not shown. However, even for the seasons where measurements could be done without confounding effects of water stress; air and soil temperature effects could not be separated. In the investigation of Peacock (l975b) the effect of high root temperature at high or cool crown temperatures on the rate of leaf expansion or other growth parameters were not evaluated. The possibility that crown might have been dessicated at high crown temperature as a consequence of the technique used was not mentioned by Schwarz (l972). Crossette et al. (l975) found that hot dry air around stem bases of barley seedlings caused tissue dessication and this was related to decreased shoot growth. On the other hand, the plant material used in other studies cited on the tOpic, either is not a temperate grass (Watts, T972) or a Graminae (Schwarz, l972). Thus, more investigation pertinent to cool season grass growth responses to localized temperatures and adaptation mechanism to heat stress was needed. MATERIAL AND METHODS Plant material establishment procedure Mature sod pieces of Merion Kentucky bluegrass (Poa pratensis L.) were taken from the field and transferred into greenhouse flats. The flats were placed in the greenhouse under an automatic irriga- tion system. Irrigation was at a frequency of three times a day for three minutes each at equal time intervals. In addition, the plants received about 4 liters per flat of a modified nutrient solu- tion (Hoagland's No. l solution) with a 2:l potassium to nitrogen ratio (Appendix Table l). The plants were clipped weekly to a height of 4.5 cm for 4 weeks. After this acclimatation period to greenhouse conditions, the sod pieces were broken into tillers having equal number of leaves. the tillers were then placed in waxed cups TO cm diameter and 8 cm deep, containing below a 50-50 mixture of silica sand l cm deep layer Of vermiculite. Holes were punched in the bottom Of the waxed cup to provide drainage. The cups with the plants were then transferred to a growth chamber which was maintained at 22 C day l6 C night for another 4 weeks. The growth chamber was set on a T6 hr. photoperiod with T9 20 a photosynthetically active radiation (PAR) level of T200 mEm'ZseC"1 and total radiation of 40 Wm"2 from mercury and sodium lamps.1 The cups were rotated every day according to a predetermined randomized plan to avoid environmental variation that may have occurred in the chamber. Every day at the beginning of the photo- period, each cup received TOO ml of the same modified nutrient solu- tion plus TOO ml of tap water 6 hrs. after the photoperiod began, and again 3 hrs. before it ended. The tillers were considered established when new tillers developed from the parent plants which occurred at the end of the third week. The plants were again clipped and kept under this management until a tiller was placed under temp- erature treatment. Method for Temperature Treatment of Plants A system was developed in order to control leaf, crown and root temperature independently from each other. Leaf temperature control Leaf temperature was provided by a walk-in environmental growth chamber maintained at 22 C day, T6 C night and a photoperiod of T6 hrs. Light source was from fluorescent tubes and heavy duty incandescent bulbs. Light was measured with a Lambda Li-l70 Quantum/ Radiometer/Photometer at the turf canopy height. PAR was measured at l200 mEm'ZseC'1 and 40 Wm‘z at the middle point of the growth chamber. The temperature of the air surrounding the leaves and in 1SunBrella Bench lighting fixture. Environmental Growth Chambers. Chagrin Falls, Ohio. 2T the turf canopy was measured with a thermometer placed both above and in the canopy at the base of the emerging shoot from the insulat- ing chamber of the crowns. These temperatures were consistent with growth chamber air temperature, except where the crown was exposed to a higher temperature than the leaves. In this case the tempera- ture in the turf canopy was one degree centigrade higher. Crowns temperature control chambers A total of T6 chambers for crown temperature control (CTCC) were made each from two "U" shaped plexiglass boxes, encased inter- nally and externally with closed cell Nalgene foam 2, which provided thermal insulation from surroundings. An illustration of the char- acteristics and dimensions for one of these chambers is shown in Figure T. Two copper pipes were glued to the bottom of the "U“ shaped plexiglass boxes, through which temperature controlled water was circulated by a pump. The copper pipes were connected by their inlets and outlets to the respective cool or hot water manifold and drainage pipes with tygon tubing. The CTCC were arranged 8 on top of each styrofoam ice chest that was the mist media environment for root growth. Each CTCC was used as a replicate for a treatment, thus each chest held two treat- ments each with four replicates. 2Nalgene clean sheets, white cross-linked polyethylene foam, l2 in wide l/8 in thick from Nalge Sybrom Corporation. Rochester, N. Y. T4602. 22 .conEmzu esp do mcowmcme_c new Eccmm_o AQUPQW conseso .ococoo mcspmcmaEmu czocu--._ mczmwd _. _. r F a chem A wnzm mmamOO ww<._.0_xw._m I....I.O... ..... . .O... . ....... . .OI....I..............”.“...........".. .”..0........”...”............I . ........... ’. ’Ih'.."..’....'.. :5 mi .to m A 5(Ou qgwo DmeJU..D\_ mm<._0.xm..a c e...— a A Bio 58%. ._ ...........O.......OO. I......IOOOOOOOOO...OO .0 mw(..0.xw._n :3. .O... . .. O... §cmc new conseco _ocucoo mczumchEmu czoco mg“ a. “cosmomfia cm_.w»--.m mcamwu \7 thOC mum 5(10 62:00: thOm 20.0mm I2>>Om0 new mm EON-1m . 230....0 woz uh.4:0_2mm> ma?— Cmaaoo l I mammahw LUO 9'17 mOZEEJU e 25 Figure 3.--Illustration of the system designed to independently con- trol crown and root temperatures of Kentucky bluegrass. 26 puOALDm GOO; 02w 20.53sz 9.9" It; a. .. 2.: :8... 303:2: connoo muzzhzoo O O muzzhzoo I h./.oaQ00 ow 3 3. .A. 5.350 4.00 Emma—OUT ‘2 I In A; .. _ T _ _ \\ 20:3 coo; . . . . _ .20 . 2932206 KOPOE _ 5.300 95...: _ a .82 5320;; .o no. :0 a Iv _ ITITIHNHHHHHHH 111111111111111111111111 \L |.v E. .51».on IV -111111-111-111-111:TIIITTTTITIIIWI. Iv common 0» JOEbZOU wKDhwD .303 .000 ._o go: oh. W A a. :3: 2.5 092.35 .o>n_ 27 At the bottom of each box, a 3/8 in internal diameter (1.0.) copper coil was placed, through which Water circulated for tempera- ture control Of the nutrient solution, mist and roots. Root temp- erature was monitored by inserting mercury thermometers at different depths in boxes. The COpper coil provided for constant temperature for both the nutrient solution and the mist. Nutrient Solution Misting System The system was similar to that used by Zobel, Tredici and Torrey (T976). A 9 cm wide x 78 cm long x 2 cm thick wood support was placed about T cm from the top of each box, and holding a frac- tional horsepower motor3 with l.4 Hp, 3450 rpm, 0.6 amp and ll5 volts. A stainless steel shaft 25 cm long with l.3 cm outside diameter (0.0.) at one end was made and attached to the motor shafts. At the smaller diameter end of the shaft a plastic Spinner4 was attached with epoxy glue. The top Of the spinner was immersed 2 cm into the nutrient solu- tion at all times. The Spinner was placed at the middle of each box to provide for even distribution of the mist. It was necessary to use an aspirator in order to obtain desirable distribution in the upper center portion of the root chamber. The aspirator was also used to keep the roots moist when the nutrient solution was exchanged. For this the aspirator inlet tube was withdrawn from the nutrient solution and immersed into a 50 ml beaker containing fresh nutrient solution. 3Howard Electric Company, 480T Bellevue, Detroit, MI 48207. 4Northern Electric CO., P.O. Box 469, Waynesboro, Miss. 39367. 28 Cool and Hot Water Circulation System Each of 2 manifolds were built with a l-T/4 in.internal dia- meter (1.0.), 80 cm long copper pipe caped at one end. A 3/8 in. (1.0.) reduction "T" at the other end provided the outlet to the copper coil in each mist box. The other inlet of the ”T" was con- nected to the respective pump for cool or hot water by a l-l/4 in. 1.0. hose. All along the 80 cm long copper pipe, pairs of holes were made l/4 in. diameter, 4 cm apart from each other and 8 cm away from the next pair of holes. A 3 cm long T/4 in. (0.0.) copper tube was soldered in each hole. All other junctions were prepared in the same manner. Each pair of these manifold outlets were connected to the corresponding CTCC with tygon tubing and plastic connectors. Laboratory clamps on the tubing allowed for withdrawing of any CTCC at any time from the system. All copper pipes and hoses were insu- lated with flexible foam rubber-like insulation pipes l-l/2 in. (I D.) to reduce heat exchange. Source of cool and hot water A cooling unit5 and a water bath6 were placed on the floor of the growth chamber (Figure 3). The coil of the cooling unit was immersed in a 43 cm wide, 73 cm long and 34 cm high styrofoam ice chest which was used as the container for cool water. Holes were 5Constant Flow Portable Cooling Unit with microtol controlling thermostat. Blue M Electric Company, Blue Island, Illinois 60406. 6Refrigerated shaker water bath. Model MSB-3222A-l. Blue M Electrical Company, Blue Island, Illinois 60406. 29 made in the lid of the ice chest for drainage hoses and the coil head. The container needed to be filled with water once only, throughout the investigation. The cooling unit maintained a 20 C constant water tempera- ture, which varied up to 22 C during the day and TB C during the night. The water bath unit temperature was adjusted to 34 C. A timer was set to automatically turn off the water bath during the 8 hr. night period. In this way, the water heated to 34 C during the day slowly dissipated its heat to a temperature of 24 C in about 6 hours. The water at 20 C and 34 C was then circulated to the res- pective manifolds by two pumps.7 Growth Chamber Procedure The plants were again broken into single tillers and the sand and vermiculite washed off the roots with water. The tillers were trimmed to five leaves and placed into a CTCC as shown in Fig- ure 2. A total of 32 tillers were placed in each CTCC. Sources of environmental variation were reduced by alternat- ing cool and hot CTCC on top of the boxes. Thus, each treatment had at least one replicate adjacent to the spinner motor mount. Additionally the 32 plants on each CTCC were divided into 4 sections of 8 plants. Only 2 sections chosen at random in each 7Teel Laundry Tray Pump. Dayton Electric Mfg. CO., 5959 W. Howard St., Chicago, Illinois 60648. 3O device constituted the experimental unit on which dry weights and innovation number were measured. The remaining l6 plants were used for leaf extension measurements. After one week of acclimation the plants were clipped again and the temperature regimes imposed. The dry weight of the clippings was statistically analyzed and no significant differences in growth were detected. The four crown-root temperature regimes were 22-22 C day and l8-l8 C night, 22-34 C day T8-24 C night, 34-22 0 day 24-l8 C night and 34-34 C day 24-24 C night. The treatments were imposed for a 5 week period. Only day temperature is given in the data tables and figures. Growth Response Measurements Growth responses to the crown and root temperature regimes were determined by measuring dry weight of clippings, stubble, crowns, crown-region roots, rhizomes, rooting chamber roots and the total dry weight of the plant. By relating the dry weight of the roots to that of the shoots, root/shoot ratios were calculated. From a subsample of four plants drawn from each replicate, the number of crown-tillers, rhizome-tillers, and rhizomes were recorded. The rate of leaf extension was also measured. Clippings above 4.5 cm were harvested weekly at the beginning of the photoperiod. The clippings were placed in labeled paper bags, dried in a forced-air oven at 80 C for 24 hours and the weights recorded after the tissue cooled in a dessicator. Total accumulated 3T dry weight of clippings was calculated by adding the weekly yields of clippings. The time between harveSt of clippings and drying did not exceed one hour. After the fifth weekly harvest of clippings, the CTCC's were removed from the growth chamber, placed into double plastic bags and transferred to the laboratory. Roots growing in the rooting chamber were cut from the rest Of the plant with a razor blade at the lower side of the insulating chamber for crowns (see Figure 2). The excised roots of the T6 plants were then cut in 5 cm sections to determine distribution with depth. Since roots in the high mist chamber root temperature did not extend longer than 35 cm, comparisons were done up to this depth. In treatments where roots extended longer than 35 cm, the dry weight Of remaining sections were added and recorded as depth greater than 35 cm. Stubble consisted of material above the CTCC including stems, leaf sheaths, new and old leaves and tillers (see Figure 2). The dry weight of material growing in the CTCC was determined after the number of tillers were counted. The crown was considered to be stem bases and 2 or 3 mm of roots growing in the crown chamber. Total shoot dry weights were calculated by adding the dry weight of crowns and stubble components to the total accumulated dry weight of clippings. Crown-region roots were roots that grew in the CTCC. The vermiculite was washed off from these roots and dry weight was det- ermined. The dry weight of crown-region roots and rooting chamber roots were added to determine the total dry weight Of the root system. 32 Rhizomes were considered to be extravaginal secondary shoots growing horizontally from the crown tissue. A rhizome with at least 2 young leaves was considered a rhizome-tiller. The rhizome-tiller weight was added to the rhizomes that had not developed into tillers to give the total rhizome dry weight. Total dry weight of the plant was determined by adding the total dry weight of clippings accumulated during the 5 week period to the dry weight of all plant parts. The number of rhizomes, rhizome-tillers and crown tillers was counted from a subsample of 4 plants per replicate. Crown- tillers were considered to be those visible tillers growing as extravaginal shoots developed from the meristematic tissues at the crown. The total number of rhizomes was calculated by adding rhi- zome and rhizome-tiller numbers. The total number of tillers like— wise, was the total of crown-tillers and rhizome tillers. The total number of innovations resulted from adding the total number of tillers to the number of rhizomes. After counting, each plant was added to the remaining l2 plants of each replicate for the determina- tion of the dry weight of the different plant component previously described. In order to analyze the relationship between roots and shoots two separate root/shoot ratios were calculated. One included both dry weight of crown-region and rooting chamber roots compared to the total shoot dry weight. In the second root/Shoot ratio, crown- region roots were not included. Both ratios were calculated since 33 crown-region roots did not grow in direct contact with the nutrient solution mist, and in some cases were exposed to a different temp- erature regime than roots growing in the rooting chamber. Thus a significant contribution of crown-region roots to shoot growth, if any, could be detected by not including its weight into the total dry weight of roots. The rate of leaf extension was measured daily on the youngest visible leaf not more than T5 mm long; from its tip to the Tigule of the youngest fully expanded leaf which was used as a datum point. The data was recorded during the second and fourth week after temp- erature regimes were imposed. . Values stated in tables or shown in figures are the mean of four replications. Analysis of variance was used to detect signi- ficant differences and Duncan's Multiple Range test was used for mean separation. RESULTS The Effect of Crown and Root Temperature on Dry Weight Production Clippings The data in Figure 4 shows the effect of the temperature regimes on weekly clipping yield. Dry weight of clippings did not differ significantly at the different temperature regimes at the end of the first week (Figure 4a). In the next two weeks clipping growth greatly increased in all treatments except at 34-34 C and significant differences were detected among temperature treatments (Figures 4b and 4c). At the end of the second week higher yields were found for plants with the crown exposed to the lower temperature (22-22 C and 22-34 C regimes). However, plants at high crown temperature but with cool root temperature (34-22 C regime) had statistically similar yields. The lowest yields were from those plants with both the crown and roots at the higher temperature (34-34 C regime). During the third week the 22-34 C regime had the greatest yields but it did not differ significantly from the 22-22 C or 34-22 C regimes. The 34-34 C regime showed again the lowest yield and differed significantly only from the 22-34 C regime. During the fourth week (Figure 4d) the data shows signifi- cantly higher clipping yields in the 22-22 C regime, and similarly 34 40. WEEK 3 2 35 3' tuna/6w ‘SIHOIaM A80 9Nlddl10 22222234342234,“ 22‘” 22-34 3422 34-34 .2:- N 538é0€SEéeéo 0 N 5 a III 3. ' n\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ a Q . . 55?. 8917?.an :5 11;; o .. N, i: ' g: a “’ v- u: i «1:33, 2 st N: géeéoéeé’eééo cnowu - ROOT TEMPERATURE , °c Figure 4.-The effect of crown-root temperatues on weekly clipping yield of Merion Kentucky Bars within the same week having common letters are not significantly different at the 5% level by Duncan's Multiple Range Test. bluegrass. 36 reduced yields when either crowns or roots were exposed to high temp- erature (34-22 C or 22-34 C regimes).' Plants with both crowns and roots at high temperature had again the lowest yields and differed to all others. At the end of the fifth week (Figure 4e), the statistical pattern Of clipping yields was identical to those from the previous week indicating shoot growth had stabilized. The data in Table l and Figure 4f shows the total accumula- ted dry weight of clippings over the five week period. When either crowns or roots were exposed to the high temperature (34-22 C or 22-34 C) regimes, total accumulated dry weight of clippings did not differ significantly from each other or from plants having both crowns and roots at the cooler temperature (22-22 C regime). How- ever, when both the crown and the roots were subjected to the high temperature (34-34 C regime) the total accumulated dry weight of clippings was significantly reduced. Stubble and Crowns Stubble dry weights did not differ significantly among all temperature regimes. Yields were almost identical except for those from the 34-34 C regime which had the lowest weight (Table T). This regime seemed to have the higher proportion of dead to living leaf tissue, but this aspect was not measured in this study. Crowns of plants exposed to the cooler temperature (22-22 C and 22-34 C regimes) had significantly higher dry weights than those crowns exposed to the higher temperature in the 34-22 C and 34-34 C regimes (Table l). Thus, high crown temperatures appeared to exert a negative effect on crown develOpment. 37 .amm» magma OFQPH—az m.couc:o x2 Pm>m_ am on» we ucmcmww_u »_a:moww_cmwm go: one caspoo mamm asp cwsuwz mcmupmp :OEEoo acm>ms mcmmz * a_.mpm om.mm ne.m am.~mm am.em ow.mk_ ne.eq om-¢m o~.mqm n_.mo_ nm.m amm.m~m nm.me mm.m_m om.m__ mm-qm om.~mm nm.~m_ mo.m_ o~.mme mm.mm mm.mpm mm.¢m. em-mm mm.aoN mu.mmm wm.mm mo.mm¢ om.- ww.qpm www.mm_ NNINN _ouop _maop uoomuczocu pear; mooom mweongm uoosm mczocu wranspm mmcwaawwo ADV mcaumcmaEmp Aucapa\mev ocmwoz Ace .mxmmz m com cmnEwco suzocm UNN o cw :zocm mmwcmm:_n Xxospcmx cowcmz do u;m_m3 xcc poo; use meo~wsc .czoco .mpnnzpm .mcwaawpo co mcsumcmqsou poo; new czoco mo “outdo one--.P whmm_ am as“ on Newcomewn >Pucmowwvcmvm uo: mom coupe. season mcw>og emcee canoe mcwuooc mamm esp cwzuvz mcmm .mmmcmm:_n xxoapcmx cowcmz cw mugmwwz act poo; consoco mcwpooc new Amoco; Eu o-mv poo; cowmmclczoco co moczpocmaEmo oooc-czocu do Homewm m:p--.m mczmwd Eu .uoz<¢ theme boom 03w «co: 1 CNN :320 .am mmaAlmm.ommN 8 mp o. m o N o mmAmm ommNoN. Nessa. .m. ...o N o o. 8 w .8 o 03. 32.63” 5.65 .3 I .3 oNNSocloom 565.8 .9. w mmIAlmN. .ommN 8 m. 9 m o-N mmAmm on R 8.. ......— o._... .m o N A “n”. V\ o M .. .. ... o M .. \ N u \ .o. o. 9 N u N .. \ .oN .. \ .8 N o \ 6 \ . \ .Om Om / s m N .. m .9. .9. w x \. m .8 .8 N O . 0o UNN ~OOETONN c320 .om . Om 4T the 22-22 C regime these roots were 27% of the total dry weight of its root system. Crown-region roots Of these two regimes were signi- ficantly different from one another and to the other regimes. Significantly reduced root weight in the crown region was found in regimes involving high crown temperatures (34-22 C and 34-34 C). Crown-region roots accounted for only l7% of the total dry weight of roots in the 34-22 C regime and only 6% in the 34-34 C regime (Figures 5c and 5d). Rooting Chamber Root Dry Weight Most of the root dry weight was localized in the first l5 cm of depth. Plants growing at the 22-22 C, 22-34 C, 34-22 C and 34-34 C regimes had 58.8%, 45.5%, 52.4% and 67.T% of their roots at this depth respectively. The data in Figures 5a to 5d shows the distribution by depth of rooting chamber root weights in 5 cm sections. For the first 5 cm of depth, significant differences in dry weights were found between plants growing at cool crown temperature and those at warm crown temperature regardless of root temperature. Cooler crown temperatures rather than cooler root temperature encouraged greater root dry weights at this depth. In the 5 to l0 cm depth and all subsequent depths, cool root temperatures rather than cool crown temperatures resulted in higher root dry weights. Root branching was greatly enhanced at this depth by cool root temperature. When the dry weights of the 5 to l0 cm depth were analyzed, it was found that plants with roots growing at 42 the cooler root temperature (22-22 C and 34-22 C regimes) not only had significantly higher root dry weights than the other regimes, but also higher root weights from the previous 5 cm section (Figures 5a and 5c). Plants exposed at the higher root temperature (22-34 C and 34-34 C regimes) had reduced root dry weights at this depth when compared to the previous 5 cm section. The distribution of dry weight of root in the remaining depths was related to root elongation from the nodal axes and branches. Root of plants at the high root temperature extended only to a depth of 30-35 cm, while root of plants growing at the cool root temperature extended to a 50-55 cm depth. The latter are shown in Figure 5 as greater than 35 cm. Roots growing in the cool root environment were more numerous, thicker, multibranched, and exhibited profuse root hairs development. These roots also had a healthy pale white color. Roots growing in the warm environment, on the contrary, were filamentous with little branching and few root hairs. These roots exhibited a dark brown color and were apparently unfunctional. Root/Shoot Ratios The data in Table 2 shows the results of root/shoot (R/S) ratios. In one analysis crown-region roots and rooting chamber roots were combined. In the second analysis crown-region roots were omitted. When crown-region roots were included significantly higher R/S ratios were found at the 22-22 C and 34-22 C regimes. A signi- ficantly reduced R/S ratio was found at the 34-34 C regime which was lower but did not differ significantly from the 22-34 C regime. 43 TABLE 2.--The effect of crown and root temperature on root/shoot ratios of Merion Kentucky bluegrass grown in a 22C growth chamber for 5 weeks. Tissue Analyzed Temperature (C) With crown-region Without crown-region Crown-Root roots roots 22-22 O.5Ta* 0.45a 22-34 0.30b 0.T7b 34-22 0.43a 0.43a 34-34 0.2lb 0.T7b *Means having common letters within the same column are not signi- ficantly different at the 5% level by Duncan's Multiple Range Test. 44 In the second analysis higher R/S ratios were obtained from plants growing at the cooler root temperature. Plants with roots at higher temperature had equally reduced R/S ratios. The Effect of Crown and Root Temperature on ’TTiTTer, Rhizomes and Total Number of Innovations Crown-tillers appeared to be more affected by a combination of both crown and root high temperatures than for any of those alone (Table 3). The highest number of crown-tillers resulted from plants with both the crown and the roots at the cooler temperature 22-22 C regime, but it did not differ from the number of crown-tillers pro— duced by plants having either the crown or the root at the high temp- erature (22-34 C or 34-22 C regimes). However, about three more tillers per plant resulted when the roots were kept cooler than the crown (34-22 C regime) than when the crown was kept cooler than the roots (22-34 C regime). Rhizome-tillers followed a similar pattern to crown-tillers. The highest number of rhizomes developing into tillers were found in the crown and root cooler temperature regime (22-22 C). Plants with either the crown or the root exposed at the high temperature did not differ significantly from each other (22-34 C and 34-22 C regimes). However, the 22-34 C regime differed significantly from the 22-22 C regime. The lowest number of rhizomes develOping into tillers were again found in the 34-34 C regime. In other words, higher root temperature rather than higher crown temperature affected rhizome-tiller production. 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