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This is to certify that the thesis entitled EFFECT OF WATER STRESS AND RECOVERY ON THE GROWTH AND DIURNAL RESPONSES OF 'REDHAVEN' PEACH TREES (PRUNUS PERSICA, L.) presented by Mary Ellen Houle has been accepted towards fulfillment of the requirements for M. S . degree in Wm Major professor 3rfl-7—Za/L/ Dateg‘fi’fl) l2; /7y6’ (J 0-7639 MSUis an Affirmative Action/Equal Opportunity Institution MSU LIBRARIES “ RETURNING MATERIALS: Place in book drop to remove this checkout from your record. FINES will be charged if book is returned after the date stamped below. EFFECT OF WATER STRESS AND RECOVERY ON THE GROWTH AND DIURNAL RESPONSES OF 'REDHAVEN' PEACH TREES (PRUNUS PERSICA, L.) By Mary Ellen Houle A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Horticulture 1984 ABSTRACT EFFECT OF WATER STRESS AND RECOVERY ON THE GROWTH AND DIURNAL RESPONSES OF 'REDHAVEN' PEACH TREES (PRUNUS PERSICA, L.) By Mary Ellen Houle Growth, growth rates, leaf water potential (0]) and stomatal conductance were observed for greenhouse peach trees (fruflu§_ persica, L.) under a rapid water stress (RWS) and a slow water stress (SW8). Leaf emergence and leaf growth were more sensitive to drought than trunk or shoot growth. Leaf growth rates (RWS) recovered fastest. Growth was reduced 20-35% for'UuaRWS,18-24% for the 50%, and 25-64% for the 25% treatment. 02 of RWS leaves declined 0.18 MPa after one week. Significant differences in stomatal conductance (SWS) followed the significant reduction in growth. Diurnal responses of greenhouse peach trees were observed during water stress and recovery. Stomatal conductance and transpiration were significantly reduced after one week. Leaf water potential declined 0.62 MPa under severe stress. Osmotic potential differed under mild stress. Turgor potential varied 0.12 MPa throughout the stress. Trunk diameters increased 5.5 and 6.5% for the stressed and control trees. No treatment differences after rewatering indicated recovery. To My Mother ii ACKNOWLEDGMENTS I am very grateful for the hours of training and guidance Dr. James A. Flore has devoted to my Master's program. I thank Drs. Gordon S. Howell and Alvin J. M. Smucker for serving on my thesis committee. In addition, I express appreciation to Dr. C. Robert Olien for the use of his equipment, to Dr. Hugh C. Price for his assistance with the Genstat program, to Walter Grant and David Torrey for their assistance with the soil moisture release curve, to Lynnel Teichman for her technical assistance, and to all the faculty, graduate students, and staff who assisted me at Michigan State. I thank Rhoda and Tom, and Bob and Myrtle for generously providing "a home away from home" on several occasions during the last year of my degree. Bill, my husband, and Elizabeth, my daughter, deserve special thanks for their support at home. m TABLE OF CONTENTS LIST OF TABLES . LIST OF FIGURES INTRODUCTION SECTION I EFFECTS OF RAPID AND SLOW WATER STRESS CONDITIONS ON THE GROWTH OF 'REDHAVEN' PEACH TREES . . Abstract . Introduction . Materials and Methods Results . . Discussion Conclusions . Literature Cited SECTION II DIURNAL RESPONSES OF 'REDHAVEN' PEACH TREES UNDER WATER STRESS AND DURING RECOVERY. . Abstract. Introduction . Materials and Methods Results . . Discussion Concluions . . Literature Cited SUMMARY LIST OF REFERENCES iv Page vii Table LIST OF TABLES Section I Initial number of leaves, shoot length, and trunk diameter measurements for the rapid water stress (RWS) and slow water stress (SWS) experiments used for cal- culating cumulative increases in growth . Effect of rapid water stress (RWS) and time (days) on the osmotic potential (05), turgor potential (up), and total leaf potential (pl), of 'Redhaven' peach leaves Effect of rapid water stress (RWS), rewatering, and time (days) on the rates of leaf emergence, leaf eXpansion, and shoot extension . . . . . . Time (days) of occurrence of statistical differences between treatments for the growth rate and water potential parmeters measured during the rapid water stress (RWS) experiment . . . . . . Effect of three levels of replacement of water used (100, 50, and 25%) and time (days) on the rates of leaf emergence, leaf expansion, shoot extension, and trunk diameter change of 'Redhaven' peach trees Time (days) of occurrence of statistical differences between treatments for growth rates and stomatal con- ductance measured during the slow water stress (SWS) experiment . . . . . . . . . . . Effect of three levels of replacement of water used (100, 50, and 25%) and time (days, h) on the stomatal conductance of 'Redhaven' peach leaves . . Growth rates for the control trees in the rapid water stress (RWS) and slow water stress (SWS) experiments Growth and growth rates, expressed as percent of con- trol, for the rapid water stress (RWS) trees at the end of the stress and recovery periods . . . . Page 15 19 20 25 32 33 34 35 36 Table Page 10. Growth and growth rates, eXpressed as percent of con- trol, slow water stress (SWS) for the trees (50 and 25% trts.) on the day responses were statistically different and at the end of the stress period . . . 37 11. Effect of rapid water stress (RWS) and slow water stress (SWS) on the final shoot length to final leaf number ratio, and the treatment effects expressed as percent of control . . . . . . . . . . . . 39 Section II 1. Air temperature (°C), relative humidity (RH, %), and available photosynthetically active radiation (PAR, uE m'2 5'1) values recorded at the time of the Stomatal conductance measurements . . . . . . . 52 2. Effect of water stress on the 0800h osmotic, turgor, and total leaf water potential (MPa) of 'Redhaven' peach leaves 59 3. Effect of water stress and recovery on the diurnal changes in transpiration rate (pg H20 mm-Z s-l) of 'Redhaven' peach leaves . . . . . . . . . . . 66 vi LIST OF FIGURES Figure Page Section I 1. Effect of rapid water stress, rewatering, and time (days) on leaf emergence of 'Redhaven' peach . . . . 20 2. Effect of rapid water stress (RWS), rewatering, and time (days) on the length of fRedhaven' peach leaves . 21 3. Effect of rapid water stress, rewatering, and time on the cumulative increase in shoot length of 'Redhaven' peach trees . . . . . . . . . . . . . . . 22 4. Calculated available water (ml/pot) for the 100, 50, and 25% treatments . . . . . . . . . . . . 26 5. Effect of three levels of replacement of water used (100, 50, and 25%) and time (days) on length of 'Redhaven' peach leaves . . . . . . . . . . 27 6. Effect of three levels of replacement of water used (100, 50, and 25%) and time (days) on length of 'Redhaven' peach leaves . . . . . . . . . . 28 7. Effect of three levels of replacement of water used (100, 50, and 25%) and time (days) on the cumulative increase in shoot length of 'Redhaven' peach trees . . 29 8. Effect of three levels of replacement of water used (100, 50, and 25%) and time (days) on the cumulative increase in trunk diameter of ‘Redhaven' peach trees . 30 9. Increase in trunk cross-sectional area vs. increase in shoot length of ‘Redhaven' peach trees for three levels of water replacement--100, 50, and 25% . . . . . . 40 Section II 1. Percent soil water and soil water tension (kPa) of control and stress treatments during the experiment . 54 vii Figure Page 2. Effect of water stress and recovery on leaf water potential (MPa) of 'Redhaven' peach leaves at 0800 and 1400 h 57 3. Effect of water stress and recovery on the diurnal changes in stomatal conductance (cm sec‘l) of 'Redhaven' peach leaves . . . . . . . . . . . 60 4. Effect of water stress and recovery on the trunk growth (mm?) of_'Redhaven' peach trees . . . . . . . . 67 viii INTRODUCTION In the last 20 years, the advent of trickle irrigation has made irrigation feasible in peach orchards where, previously, overhead sprinkler irrigation has yielded marginal economic benefit. As the technology in trickle irrigation progresses, the demand for efficient, effective, and economical schedules for peach orchard irrigation increases. Scheduling irrigation according to Class A pan evapora- tion (E or soil water status are relatively easy methods pan) (Elfving 1982); however, because only a portion of the root system is wetted around a trickle irrigation emitter, when and where to monitor soil water status become difficult questions. In addition, soil water or evaporation monitoring methods do not account for growth physio- logical status or water needs of the tree. Incorporating parameters of growth and water status could improve the efficacy of an irrigation schedule. In the process of identifying parameters for developing an irri- gation schedule, several questions surface: 1. What are the growth characteristics of the nonbearing and bearing peach tree? 2. What are the diurnal and seasonal responses of stomatal conductance and plant water potential? 3. How do the growth and water status parameters respond under water stress? 4. What is the relative sensitivity of the growth and water status parameters to water stress? Several recent papers on the growth characteristics of peach trees indicated that the growth of vegetative and reproductive struc- tures of peaches followed predictable daily and seasonal patterns. Trunk and shoot diameters flucturated diurnally with maxima before sunrise and minima during midafternoon (Kozlowski 1968, Powell 1976). Annual trunk circumference growth increased faster in nonbearing trees than in bearing trees. As trunk circumference increased, the average length of shoots decreased while the average number of shoots increased. Trunk size was also highly correlated with other measurements of tree growth and size, e.g., dry weight increments, leaf area, number of leaves, tree volume (Chalmers and van den Ende 1975). A curvilinear relationship between trunk cross-sectional area (TCA) and shoot length with correlations of 0.88 to 0.99 has been documented for peaches (Khatamian and Hilton 1977); and it was suggested that TCA was an adequate indicator of tree vigor (Khatamian and Hilton 1977, Westwood and Roberts 1970). Equations for predicting leaf emergence and leaf growth have been developed for peaches and cherry. Light, tempera- ture, degree-day accumulations, precipitation, soil moisture and days from full bloom data were among the variables included (Eisensmith et al. 1981, Haun and Coston 1983). Peach fruit growth and development were characterized by a three- stage growth curve which exhibited rapid, slow, and rapid increases in fruit dry weight (DW) increments (Chalmers and van den Ende 1975). The growth flushes of fruit DW and shoot diameter were juxtaposed during the fruiting season. During DW Stage II, the increment in shoot diameter increased as the increment in fruit dry weight decreased (Chalmers and Wilson 1978). Chalmers et al. (1981) scheduled irrigation according to the dry weight stages of fruit growth. By reducing irrigation to 12.5% of the irrigation require- ment during DW Stage II, vegetative growth was reduced without affect- ing yield. The diurnal variations in water status and stomatal function are well documented for peach, as well as other fruit trees (Chalmers and Wilson 1975, Davies and Lakso 1979, Goode and Higgs 1973, Hendirck- son 1926, Kozlowski 1968, Klepper 1968, Xiloyannis et al. 1980, Young et al. 1981). The diurnal responses have been correlated with the environmental factors--light, temperature, and humidity (Davies and Lakso 1979, Goode and Higgs 1973, Klepper 1968, Stanley et al. 1983). Stomatal conductance reached a maximum before noon and a minimum by midafternoon (Hendrickson 1926, Young et al. 1981); whereas the peak in transpiration generally occurred after midday, when temperatures and vapor pressure dificits were greatest (Kramer 1967, Landsberg and Jones 1981). Plant water potential became most negative between 1000 and 1600h, and least negative overnight (Chalmers and Wilson 1978, Goode and Higgs 1973, Klepper 1968, Xiloyannis et al. 1980, Young et al. 1981). Water flux in and out of Umeplant was the primary regulator of these diurnal curves; however, environmental factors and position in the canopy affected the extent and duration of the change (Chalmers and Wilson 1978, Klepper 1968). As the season progressed, stomatal conductance and water poten- tial values changed to reflect maturation, adaptation to the environ— ment, and accommodation of the carbohydrate and water demands of fruiting (Chalmers and van den Ende 1975, Chalmers and Wilson 1978, Davies and Lakso 1978). During DW Stage III stomata remained open longer during the day (Chalmers et al. 1983). Xylem water potential of well-watered trees remained constant between -0.5 and -0.8 MPa (Xiloyannis et al. 1980); however, leaf water potential for trees watered intermittently became as much as 0.8 MPa more negative late in the season (Chalmers and Wilson 1978), Proebsting and Middleton 1980). In addition, trees with a heavy fruit load wilted sooner after irrigation than trees with few or no fruit (Chalmers and Wilson 1978). Diurnal and seasonal osmotic adjustment of cellular solute con- centration has been reported for some plant species under water stress, including apple trees (Davies and Lakso 1978, Goode and Higgs 1973, Hsiao et al. 1976, Lakso et al. 1981). A capacity for osmotic adjust- ment to maintain turgor in peaches has been suggested in recent literature; however, the results were not consistent or conclusive (Young et al. 1981, 1982). Young et al. (1982) concluded that approxi- mately 30% of a drought induced reduction in leaf water potential could be explained, statistically, by a concomittant decrease in osmotic potential. No studies of osmotic regulation of cell turgor for field grown peach trees has yet been published. The methodology for determination of stomatal conductance, leaf water potential, and osmotic potential has been defined and critiqued (Brown and Tanner 1983, Scholander et al. 1965, Slavik 1974). Porome- try has become the accepted field method for determination of stomatal opening and stomatal resistance to water vapor and gas exchange. The principle for determining stomatal resistance with a steady state or null balance porometer, the state of the art in porometry, is simple: ”Day air is blown into the ventilated chamber at a rate (measured) just sufficient to keep the pre-determined air humidity constant. A balance is maintained between the flux of transpired water and the air flow" (Slavik 1974). Resistance is then determined from the equation -100 A “(i—3'1) f where: r = resistance (s cm‘l) r.h = relative humidity A = leaf area within the chamber (cm2) f = flux of dry air (cm3$"1) Expressing stomatal resistance as its reciprocal, stomatal conduc- tance, has become accepted because stomatal conductance was linearly related to stomatal operature (Raschke 1976). Pressure chamber methods reliably estimate leaf and xylem water potential. llueleaf is hermetically sealed in the steel chamber with the cut end of the petiole exposed to the atmosphere. Gradually the pressure within the chamber is increased using compressed nitrogen until small bubbles of xylem sap are visible at the cut petiole surface. The pressure at which this occurs is equal to the pressure required to force water from the cells surrounding the xylem into the xylem stream (Wilkins 1969, Slavik, 1974). Because the osmotic poten- tial of the xylem sap is near zero, its component of the water poten— tial is negligible (Slavik 1974). Humidification of the compressed gas, wrapping the leaf in a plastic bag, or placing dampened filter paper in the chamber will help reduCe water loss from the leaf and reduce the chances for erroneously low water potential (Davies and Lakso 1979a, b, Slavik 1974). The most reliable results of estimating osmotic potential are obtained from a pressure volume curve and with dewpoint thermocouple hygrometry. For the pressure-volume method, a pressure bomb is used to express sap from live tissue at various pressure intervals until no more sap is exuded and the turgor pressure is relieved. The mass of the accumulated sap is plotted against the reciprocal of the pres- sure. The linear portion of the curve, when extrapolated to the y—axis, intercepts the y-axis where ow = us. For the dewpoint thermo- couple hygrometry method, a segment of previously frozen leaf tissue is sealed within a chamber containing thermocouples which allow simul- taneous cooling of the thermocouple junction and measurement of the declining temperature. As the thermocouple is electrically cooled, water vapor condenses on the thermocouple junction. The electrical energy used to condense the water vapor is "proportional to the dew- point and may be calibrated in terms of water potential" (Slavik 1974). Plant parameters used to develop an irrigation schedule should reliably represent tree growth and water status, and the data should be readily obtained in the field. Trunk growth and leaf water poten- tial are possible candidates. Trunk growth has been highly corre- lated with shoot growth and other parameters of growth and size (Chalmers and Wilson 1978, Khatamian and Hilton 1977). Diurnal contraction and swelling of the trunk reflected the sensitivity of diameter changes in response to daily water fluxes in the tree (Kozlowski 1968, Powell 1976). Trunk diameters are easily measured with vernier calipers or millimeter micrometers. Constant record- ing of trunk diameter changes can be monitored with dendrometers or linear transducers (Kozlowski 1968, powell 1976). Black et al. (1977) eXperimented with supplying irrigation water in liters of water per cm TCA per cm E Adjusting TCA measurements pan for degree of canopy cover in the orchard may be necessary for esti- mating water needs from Epan' TCA was believed to underestimate tree size and may have resulted in overwatering smaller trees. Plant water potential has been proposed as an indicator of stress to be incorporated into irrigation scheduling (Anon. 1983 Proebsting et al. 1981). As an indicator of stress, xylem water potential was most reliable before dawn (Xiloyannis et al. 1980); whereas, midafternoon xylem and leaf water potentials tended to reflect the hot, dry environment more than the stressed status of the tree (Proebsting and Middleton 1980, Xiloyannis et al. 1980). Leaf position, leaf age, time of day and season, and environmental factors influence water potential (Anon. 1983, Klepper 1968, Proebsting and Middleton 1980, Stanley et al. 1983); and therefore, these factors must be considered to insure uniform sampling with minimal error. Production of soil water conditions in a pot similar to field conditions has been questioned. Wilting and soil water depletion occurred in seven to ten days after watering was terminated in several experiments with potted plants (Davies and Lakso 1979, Tan and Buttery 1982, Young et al. 1981). Soil water depletion can require four weeks in an orchard (Cullinan and Weinberger 1931, Hendrickson 1926, Xiloyannis et al. 1980). Some preconditioning may occur in trees which experience slowly developing or intermittent water stress periods. Trees preconditioned to water stress exhibited a greater tolerance to stress with less negative leaf water potential and greater stomatal conductances (Davies and Lakso 1979a). For this reason responses to a slow stress could differ from responses to a rapid stress. Studies of the growth and water status parameters were believed essential to identifying parameters best suited for developing irriga- tion schedules. The thesis was developed in two sections with the general objective to assess fiuepotential of various growth and water stress parameters as indicators of water stress. The specific objec- tive of Section I was to characterize the growth responses of 'Red- haven' peach trees under a rapid water stress and a slow water stress. The objective of Section II was to study the diurnal responses of stomatal conductance, transpiration, leaf water potential, and trunk growth during a cycle of water stress and recovery. SECTION I. EFFECT OF A RAPID WATER STRESS AND A SLOW WATER STRESS ON THE GROWTH OF 'REDHAVEN' PEACH TREES ABSTRACT A rapid water stress (RWS) and recovery treatment and two levels of a slow water stress (SWS) treatment (rewatering at 50 and 25% of the control) were applied to potted one-year-old peach trees (Prunus persica, L., Batsch, cv. 'Redhaven'/'Halford') in a greenhouse. Growth, growth rates, leaf water potential components, and stomatal conductance were observed. Occurrence of statistical differences between treatments was used to determine sensitivity to stress. Total leaf water potential was 0.18MPa less than control for the stress trees after one week of RWS. Leaf emergence was more sensitive than leaf or shoot growth; however, leaf growth rates recovered fastest after rewatering. Leaf emergence, leaf length, and shoot length were reduced by 80, 77, and 65%, respectively. Available soil water declined to 40 and 20% of the control for the 50 and 25% SWS treat- ments. Leaf emergence was more sensitive than trunk or shoot growth, while leaf growth rates were more sensitive than leaf emergence, trunk, or shoot growth rates. Leaf emergence, leaf growth, shoot extension, and trunk diameter were reduced by 58, 82, 56, 76, and 64% for the 50% treatment, and 50, 75, 36, 57, and 39% for the 25% treat- ment, respectively. Significant reductions in stomatal conductance followed with the reductions in growth within 2-7 days for the SWS experiment. 10 Introduction In the last 20 years the advent of trickle irrigation has made irrigation feasible in peach orchards, where previously irrigation has yielded marginal economic benefit. As the technology in trickle irrigation progresses, the demand for efficient, effective, and economical schedules for peach orchards increases. Scheduling irri- gation according to Class A pan evaporation (Epan) or soil water status are relatively easy methods (Elfving 1982); however, these methods may not accurately reflect the amount of soil water available to the root system because only a portion of the root system is wetted with a trickle irrigation system. In addition Epan and soil water measurements do not account for growth, physiological status, or water needs of the tree. Incorporating parameters of growth and water status could improve the efficacy of an irrigation schedule. Parameters used to develop an irrigation schedule should reliably represent tree growth and water status, and the data should be easy to obtain. Trunk or limb diameter and leaf water potential measure- ments are possible candidates. Trunk growth has been highly corre- lated with shoot growth and other parameters of growth and size (Khatamian and Hilton 1977, Chalmers and Wilson 1978). Trunk cross- sectional area (TCA) was believed to be a satisfactory indicator of tree vigor (Khatamian and Hilton 1977, Westwood and Roberts 1970). Diurnal contraction and swelling of the trunk reflected the sensitivity 11 12 of diameter changes in response to water loss and retention due to stomatal opening and closure (Kozlowski 1968, Powell 1976). Trunk diameters are easily measured with vernier calipers and millimeter micrometers and recorded using dendrometers or linear transducers (Chalmers and Wilson 1978, Kozlowski 1968, Powell 1976). When peach tress were subjected to drought stress, plant water potential became more negative (Proebsting and Middleton 1980, Xiloyannis et al. 1980, Tan and Buttery 1982, Young et al. 1981). As an indicator of stress, plant water potential was most reliable before dawn (Xiloyannis et al. 1980) because midafternoon water poten- tials tended to reflect the hot, dry environment more than the stressed status of the tree (Proebsting and Middleton 1980, Xiloyannis et al. 1980). Pressure bomb techniques for determining leaf and xylem water potential are well described (Davies and Lakso 1978, Scholander et al. 1965, Slavik 1974), and the measurements are easily made in the field. Leaf position, leaf age, time of day and season, and environmental factors were shown to influence leaf water potential, and therefore, must be considered when interpreting the results (Klepper 1968, Proebsting and Middleton 1980, Stanley et al. 1983). The production of soil water conditions in a pot similar to field conditions has been questioned. Wilting and soil water depletion occurred in seven to ten days after watering was terminated in several experiments with potted plants (Davies and Lakso 1979, Tan and Buttery 1982, Young et al. 1981). Soil water depletion can require four weeks in an orchard (Cullinan and Weinberger 1931, Hendrickson 1926, Xiloyannis et al. 1980). Some preconditioning may occur in trees 13 which experience slowly developing or intermittent water stress periods. Trees preconditioned to water stress exhibited a greater tolerance to stress with less negative leaf water potentials and greater stomatal conductances (Davies and Lakso 1979a). For this reason, responses to a slow stress could differ from responses to a rapid stress. The goal of this study was to characterize some of the growth responses of 'Redhaven' peach trees under a rapid and a slow stress. Understanding these growth responses could aid in developing trickle irrigation schedules for peach orchards. 'Redhaven' peach trees were selected because of the commercial importance of this cultivar (Childers 1978). Materials and Methods General. Two groups of one-year-old grafted peach trees (Eruflgs persica, L., cv. 'Redhaven'/'Halford') were grown in 19 liter con- tainers filled with 2 soil: 1 sphaghunlmoss: 1 sand (v:v:v) soil mixture in a greenhouse. Group I was potted in September 1981 and group II in April 1982. Each tree was pruned to two branches. The experiments were begun six weeks later, after 10-15 leaves had unfolded. High irradiation density lamps, cooling fans, and steam radiator heat were used to maintain a 15h photoperiod, a night temperature of 17:2°C and a day temperature of 30i5°C. A water-soluble fertilizer (20—20-20) at 250ppm N was applied with alternate waterings. Miticides and fungicides were applied sparingly as needed. 14 The number of leaves (no.), leaf length (mm), shoot length (cm), and trunk diameter (mm) were the growth parameters measured. The number of leaves were counted from the base and included every leaf longer than 2mm. Leaf length was measured from the petiole base to the leaf tip. Shoot length was measured from the base of the shoot to the tip of the newest emerging leaf or tip of the terminal bud. Trunk diameter was measured with a digital micrometer (Mitutoyo, Japan, Model 193-101, range 0-25i0.05mm) at marked locations on the trunk 10-12 cm above the graft union. Cumulative increases in number of leaves, shoot length, and trunk diameter were calculated based on the measurement made on day 1 of each experiment (Equation 1, Table 1). Equation 1: Cumulative increase in growth n 1 where: C = cumulative increase in the parameter measured (mm, cm, or no.) Mn = measurement on dayn (mm, cm, or no.) M1 = measurement on day1 (mm, cm, or no.) Rates of leaf emergence, shoot extension, and trunk diameter change were calculated for two— to four-day intervals for each experiment (Equation 2). 15 Table 1. Initial number of leaves, shoot length, and trunk diameter measurements for the rapid water stress (RWS) and slow water stress (SWS) experiments used for calculating cumu- lative increases in growth. Parameter Treatment Measurement on day 12 Rapid Water Stress No. of Leaves Control 24.1 i 3.1 Stress 28.3 i 3.2 Shoot Length (cm) Control 26.8 i 7.1 Stress 38.2 i 9.4 Slow Water Stress No. of Leaves 100% 32.0 i 4.4 50% 31.9 i 3.7 25% 32.8 i 3.0 Shoot Length (cm) 100% 54.7 i 14.5 50% 51.3 i 13.8 25% 53.5 i 8.2 Trunk diameter (mm) 100% 9.98 i 0.24 50% 9.71 i 1.13 25% 9.76 i 0.65 ZEach measurement represents an average of 4 trees. yMeans within parameters are not statistically different (LSD, 5% level). 16 Equation 2: Growth rate M — M R =._E_fi__2 where: R = growth rate (mm, cm, or no. day-1) MC = current measurement (mm, cm, or no.) Mp = previous measurement (mm, cm, or no.) Water status was monitored with stomatal conductance and water potential measurements. Stomatal conductance was determined with a steady-state porometer (Li—cor, Inc., Lincoln, Nebraska, Model 1600) on the abaxial side of a recently expanded leaf. The same leaf was used for total leaf water potential (pl) measurements using a pres- sure bomb (PMS, Corvalis, Oregon) and the technique of Scholander et al. (1965). The leaf was sealed in a 'Ziploc' bag, kept in the dark in a cooler and frozen to -20°C two hours later. The osmotic potential (as) was determined by dewpoint hygrometery (Wescor, Inc., Logan, Utah, micro—voltmenter, Model HR-T 33 and chamber, Model C-52) using one thawed 5mm disc from each leaf and a 15—minute equilibration time in the chamber. The data were analyzed as a randomized, complete block with four replications. The trees were blocked by trunk diameter size. Each date was analyzed separately. For the analysis, a value for each one tree plot was calculated from the average of two measurements per tree, one from each branch. Only one trunk diameter measurement was made 17 per tree. Significant differences between treatments were determined by a least significant difference (LSD) statistic at the 0.05 level (Steele and Torrie 1980). Rapid Water Stress Experiment (RWS). A rapidly induced water stress situation was created by withholding water until the leaves wilted and the soil water tension approached 60kPa. The number of leaves, leaf length, and shoot length were recorded beginning at 0800h every three to four days during the prestress period, day 1-5 (October 15-19, 1981), during the stress period, day 6-16 (October 20-30, 1981), and during the recovery period, day 17-33 (October 31-November 16, 1981). For the leaf length measurements, leaves emerging on day 1, 12, and 22 were collectively named Leaf Group (LG) A, B, and C, respectively. Plant water potentials were determined at 1300h every three to four days during the stress period. Slow Water Stress Experiment (SWS). A simulation of gradual soil water depletion was created by watering some of the trees with 50 or 25% of the volume of water retained per watering period by the fully watered trees. Every tree received 2 liters of water every two to three days for two weeks. The water drained after 24h was measured and the volume subtracted from 2 liters to determine the amount of water retained. An average volume of water retained per day for the two—week period was calculated to be 400:50ml. Of this volume 50 to 25% (i.e., 200ml and 100ml) was applied every two to three days to the stress treatments, while the control trees continued to receive 18 2 liters. After 16 days the volume of water applied to all trees was adjusted for growth and increased transpiring surface based on an average volume of water retained per day by the control trees during the 16-day period. The number of leaves, leaf length, shoot length, and trunk diameter were recorded beginning at 0800h every two to three days from day 1 (May 20, 1982), two days before the stress treatments were started, and were continued until day 29 (June 19, 1982), when the stress was relieved. For the leaf length measurements, leaves emerge ing two weeks before day 1, on day 1, and on day 12 were collectively named Leaf Group (LG) A', B', and C', respectively. Stomatal con- ductance and transpiration were measured at 1000 and 1400h three times during the stress period and one day after rewatering. Results Rapid Water Stress Experiment. Plant water potential was used as an indicator of the stressed status of the trees (Table 2). On day 6, the first day of the stress period, no statistical differences between treatments for up, ms, or Y1 were observed. Three days later, Y5 differed significantly, but up and Y1 did not. After one week with no additional water Yp and Y1 differed significantly, however, as did not. The net result of the RWS treatment was reduced increases in the number of leaves, shoot length, and leaf length of emerging (LG-B) or rapidly expanding (LG-A) leaves (Fig. 1, 2, 3). The length of leaves emerging after rewatering (LG-C) was not affected by the stress (Fig. 2). 19 Table 2. Effect of rapid water stress (RWS) and time (days) on the osmotic potential (ms), turgor potential (up), and total leaf potential (ml), of 'Redhaven' peach leaves. TimeZ wsy wpy ply (days) Treatment (MPA) (MPa) (MPa) 6 Control -2.98 1.58 -1.40 Stress -2.87 1.06 -1.71 9 Control -2.38 a 1.08 -1.42 Stress -2.80 b 0.98 -1.82 13 Control -2.60 1.42 a -1.28 a Stress -2.82 0.98 -1.81 b 2Number of days after initiation of experiment. Water was withheld between day 6 and 16. yMean separation within time by L50, 5% level. 20 Q N (fa—t .a u ,1 111 CONTROL 8 '4 r-\ o STRESS m: a .. a b g ‘2 '4 u ‘z (:1 a a «a .. a F. m b 1: a u NJ '4 a) “>’ m“ a a J u a (0‘ b .. ‘4 m- / / . . o“ ' 1 1 1 1 I T I 0 6 10 15 20 26 30 36 TIME (DRYS) Figure 1. Effect of rapid water stress, rewatering, and time (days) on leaf emergence of 'Redhaven' peach. Mean separation within time by LSD, 5% level. 21 , N v-u-i N a a a a- 1:1 CONTROL ., "‘ '4 a o STRESS '3 b b . A m- b ‘ b 1: '- s o 53 a b I u v. a b ca“- b 2 "‘ '4 LLJ A - & LEAF GROUP A " a u: - .J as b u ., LEAF GROUP 8 ‘0 u ' b u u .3 b m - a ‘4 a ., LEAF GROUP 0 c d L I o I I r l l l r o 5 10 IS 20 25 30 as 40 TIME (URYS) Figure 2. Effect of rapid water stress (RWS). rewatering, and time (days) on the length of 'Redhaven' peach leaves. Mean separation by LSD, 5% level. 22 48 cun INCREASE IN SHOOT LENGTH (CM) Figure 3. TIME (DRYS) a u a '1 [:1 CONTROL (9 STRESS , '1 b a b 9 '4 l“ a '1 b a 9 b 9‘ ///’ L J I I I I I I I 5 10 15 20 25 3O 35 40 Effect of rapid water stress, rewatering, and time on the cumulative increase in shoot length of 'Redhaven' peach trees. level. Mean separation within time by LSD, 5% 23 The effect of water stress and recovery on the growth rates and the occurrence of statistical differences between treatments was used to determine the sensitivity of these growth parameters to water stress (Table 3 and 4). Leaf emergence rate was more sensitive to water stress than leaf or shoot growth rate. The growth rate for leaves emerging during the stress period (LG-B) was more sensitive than the growth rate for leaves rapidly expanding at the same time (LG-A). After rewatering, leaf growth rate recovered faster than leaf emerg- ence or shoot growth rate; however, the recovery of leaf emergence rate was more complete. About two weeks elapsed after rewatering before the shoot growth rate for stressed and control trees were similar. The growth rate of leaves emerging three days after rewater- ing (LG-C) were unaffected by the stress. Slow Water Stress Experiment. The amount of water available at field capacity was determined to be 4000:150 ml per pot. The 50 and 25% watering treatments resulted in a progressive decrease in avail— able water (Fig. 4). By day 24 the available water had decreased to approximately 40 and 20% of the control for the 50 and 25% treatments, respectively. Growth was significantly reduced for all stress treatments except shoot growth for the 50% treatment. The significant effects Of the SWS on the increase in growth were first observed 12-16 days after treatments were initiated (Figs. 5, 6, 7, and 8). From most to least sensitive, the order of sensitivity to the stress was leaf emergence, trunk growth, shoot extension. The duration of the stress was 24 ._m>m_ Sm .om4 An wavy cwguwz :owpmcmawm :82.A .oH can o Ame :mmzpmn vpmczpwz mm; gmpmzN om.H mH.H nmm.o nnm.o nw¢.o nom.o om.o OH.H wH.H mmmgpm m¢.H mm.H mmm.H mmm.~ mmm.H wmm.H mm.H mm.H mm.o Fogpcoo xflfiuzmn Eov cowmcmpxm poogm mN.H mm.o o¢.o mmmcpm oH.H mm.o mm.o poeucou xAfitxmu Eov u azogu mmmS No.0 mm.o mm.o om.o w~.o nmo.o mmmcum mm.o mo.H mm.o om.H m~.o mn¢.o Focucou xAH-qu Euv m azogo mam; mH.o mm.o mN.o mm.o mm.o nmv.o mw.o om.o mm.o mmmcum No.0 mm.o mH.o m¢.o mo.H w~o.~ mo.H mm.o om.o Focucoo AAfiuxmn Euv < azogw tom; ano.o 00.0 mo.o mm.o noH.o om.o nmm.o mm.o om.o mmmcpm nmm.o ow.o mo.o mm.o mon.o mm.o mmo.o mm.o Amm.o Pocpcou AAH-»mu .ozv mucmmgwsm wmmo mm om mm mm mH mH NH w m ucmEumeH NAmxwuv acmewcmgxm So cowpmwpwcH empw< me_k .cowmcmpxm goesm vcm .cowmcmaxm wmmF .mocmmcmsm mmm— mo moan; ago :0 Amxmcv mew“ use .mcwcmuw3mg .Amva mmmgum Loam; ovum; oo powwow .m oFQBR 25 .mmmcu Pogpcoo mcu Low.mpmc any umuwmoxw mmmcp ummmmgpm asp mo mom; mocmmgmsm Comp mg» cows: co when msp mmumcmwmmc «x .nmcgzouo fipw>wp Sm .omAV mmucogmoewv quwpmwampm sovcz :0 when on» mmpmcmwwmu *N -k 'I‘ -k -k Fwwucmpoa somczh Fwwpcmuom owuoEmo Fe_pcapoa cam; _mpoe mepcmpoa Lopez cowmcmpxm poozm o angw Camp m macaw one; < macaw com; mocmmgmsm mam; mmpmm spzocw uo_ama mmmcum mm om mm om mH 0H m ».Np:aewcaaxm mzm co cowpa_ewcH Laoc< Amzeev mace cmmemcma .pcmswcmaxw Amzmv mmmcpm Lopez swam; ogp mcwgze uwcsmmme mcopmemcma mepcmpoa Loom; can mp8; cpzocm as» Low mucprmmLp :mmzuwn Nmmucmcmwewu _wowpmwpepm $0 mocmgcsouo Co Amxouv OESP .e mpnmk 26 4800 4200 \9 secs r——1 I I 2400 3000 RVRILRBLE H20 (ML/POT) 1000 [I] 100% REPLACEMENT 1200 O 50% REPLACEMENT A 25% REPLACEMENT 600 1 u "0 0 4 8 12 15 TIME (DAYS) Figure 4. Calculated available water (ml/pot) for the 100, 50. and 25% treatments. 32 16 27 LERVES EMERGED (NUMBER) 1 Figure 5. 111 1007. REPLACEMENT a o 50% REPLACEMENT '4 a l A 25% REPLACEMENT '2 a li a U a b b b c 3 3 4 '4 5 C . J b '° c c i _ _. I I I I I I r 4 8 12 16 20 24 28 32 TIME'fDHYS) Effect of three levels of replacement of water used (100, 50, and 25%) and time (days) on leaf emergence Of 'Redhaven' peach leaves. Mean separation by LSD, 5% level. 28 E’ a a u 5 &J a ‘ LEAF GROUP A' a ‘ I 'b 2- - b 9 b u '3 b as b 2: 'b E b 8 m- u a, a as " b c: b b 5 ~ b _I g- b L c 2 3 LEAF GROUP 8' _" .1 g I" C: G) )— O .— a- ' m 1007: REPLACEMENT a- o 507: REPLACEMENT 4, ZSZIFEEMJKXQWENT Cb 5r :6 15 20 25 35 SE 40 TIME (DRYS) Figure 6. Effect of three levels of replacement of water used (100, 50, and 25%) and time (days) on length of 'Redhaven' peach leaves. Mean separation by LSD, 5% level. 29 4o- CUM INCRERSE IN SHOOT LENGTH (CM) 01, Figure 7. a 1:1 100% REPLACEMENT a ,J o 50% REPLACEMENT " A 25% REPLACEMENT a A ab a ab -. A ab ab ‘ '4 l b b b — :j’ /. /" F I I T I I I 4 8 12 16 20 24 28 32 TIME (DHYS) Effect of three levels of replacement of water used (100, 50, and 25%) and time (days) on the cumulative increase in shoot length of 'Redhaven' peach trees. Mean separation within time by LSD, 5% level. 3O 24 CUM INCRERSE IN TRUNK DIFl (MMIIIOI Figure 8. a m 100% REPLACEMENT u 0 50% REPLACEMENT . . a A 25% REPLACEMENT u a M b 9 a M b a " '1 C a c " b c ‘ a b b J 'i/ T“ ' I I I T I I I 4 a 12 16 20 24 28 32 TIME (DRYS) Effect of three levels of replacement of water used (100, 50, and 25%) and time (days) on the cumulative increase in trunk diameter of 'Redhaven' peach trees. Mean separation within time by LSD, 5% level. 31 sufficient to halt leaf emergence for both stress treatments, and shoot growth for the 25% treatment. The rapidly expanding phase of leaf growth became irregular and shorter for the stressed trees. The order of sensitivity of the growth rates in response to SWS was unlike the order for a RWS. For the SWS, the order was LG-B' and C' (for the 25 and 50% treatments), leaf emergence and trunk diameter (25% treatment), trunk diameter (50% treatment), shoot exten- sion (25% treatment), leaf emergence (50% treatment),sh00t extension (50% treatment) (Tables 5 and 6). Although LG-C emerged nine days after treatments were begun, it was ranked highly sensitive because a significant reduction in rate occurred within five to seven days after emergence. A similar response was Observed for LG-B'. After the growth of the stressed trees was beginning to differ from the control trees, differences in stomatal conductance were also observed (Tables 6 and 7). On day 17, 1000h stomatal conductances were significantly less for the 25% treatment. At 1400h both the 25 and 50% treatments were significantly different. One day after rewatering there were no differences in stomatal conductance. A comparison of the effects of the two stress situations was simplified because growth rates for the control trees were similar for both experiments (Table 8). Further generalized comparisons among parameters, between treatments and between experiments were made by expressing the data from each parameter as a percent of the control for selected times in each experiment (Tables 9 and 10). An estimate of internode length was derived from a ratio of shoot I32 noe.o aoe.o noo.o amo.o nm_.o uc~.o Ne.o nom.o mm.o mo.o o~.o acm.o amw mom.~ aoo.o mom.~ am~.o moo.o amm.o mm.o amm~.c mn.o oo.o mv.o amc.o sow anew.“ use.“ a-.~ awe." amw.o amo.o mc.o mmm.o oe.o mo.o oe.o umv.o Noo— Ao~ x ataav say accuse Louasova xcagp am~.o am_.c Om~.o 0mm.o a-.~ mm.“ mm.~ noa.o mm.~ umm nm~.o nmo.o akm.o nwo.o a~m.¢ he." on." own.“ mm._ Rom amn.o ao~.~ onm._ am~.H cha.~ -.~ mv.~ amm.~ oo.~ goo“ Afitxuv Euv :ovmcmuxu poogm ow.o aom.o amc.o no~.o ao~.o om.o -.o “mm mm.o aom.o annm.o ace.o amov.o m~.o o~.o Nom m~.~ new." aso.~ coo.~ moo.o me.o o~.o mac“ Authau Eu“ .u Sacco one; em.o mm.o an~.o am~.o amm.o ame.c new.“ Na.o am~.o acm.o amm.o noon.o Nmm om.o om.o oom.o nomm.o comm.o pmm.o no~.~ -.~ am~.o amm.o amm.o omm.o Rom m~.o o~.o non.o omm.o mom.o moa.o ans.“ n~.~ amo.~ nom.o amm.o am~.o woo" afitamv soy .m asocu Gum; nos—.o om.o mm.o oe.c om.o Nm~ am~.o mm.o oo.o mo.o oa.o Rom mon.o oo.c mm.o no.9 cm.c “cog A~1aac Sou a gas :3 mo~.o noo.o no~.o amo.o aoo.o o~.o “v.0 ammuo noo.o om.o om.o noe.o .umm noo.o amo.o noo.o ao~.o amov.o om.o -.o nme.o nme.o om.o mm.o nmc.o mom mom.o am~.o nom.o aoa.o mm~.o m~.o om.o mm~.o aoo.o om.o mm.o Amen.o aoo~ A thou .ozv muse Loam Cum; aw mm em - mH N“ m" Nu m N m m acoEummL» Namxaov acmsvgoaxm mo covumvu_=_ coaw< mevh .mmmcu sumac .cm>c;cmm. Go wmcagu Loumsu.c gaze» use .:o_m:maxo uoocm .covmcoaxo Camp .oucmacmsm unm— we moan; any so Ammocv wsvu can Aumm can .om .oofiv Gum: Luau: mo acmsmuapamg mo upo>up omega we uummum .m m—neh 33 .Amo.o u a .omnv noggzooo mmocmcmnmwn ragwmepmpm “wavy on“ gown: no mAmn mmpmcm_mmnsz .m awn no nmpn_u_cw mcm3,mucmeunmgp~ x mm k om :oomH « mm om nooofi wocnponncou PnanOpm k r k a k k x mm k k k k om Lmumewo xczgh k k k k mm x r k om cowmcmHXm woozm k k r k mm r k k . om .o asogw wmwn k k k x k E k k k mm « k k a k x 0m _m QDOLo %wmA * mm om .< macaw Lean k k R k k k mm k k k k k k om mucmmLmEm $mm4 mmpna npzocw “ L nowgma mmmgum om mm ON ma OH m H unmEpnmEH cmmenEna ».~pcmewcmaxm m3m mo cowunwp_cH memn Amxnnv we?» awcmaxm Amzmv mmmcwm noun: 30pm mcn m:_czn nmczmnme mucnponncoo annEOpm new cpzogm Com mpcmEpnmEu cmmzpmn Ammucmcmwwwn Fnovpmwpnpm no nonmagnouo Co Amxnnv .ncms mmpnc mark .0 mFQnH 34 Table 7. Effect of three levels of replacement of water used (100, 50, and 25%) and time (days, h) on the stomatal conductance of 'Redhaven' peach leaves. Stomatal conductance (cm s'l)y Time (days)z Treatment Time (h) 1000 1500 1 100% 1.60 1.75 50% 1.70 1.76 25% 1.76 1.77 12 100% 1.94 2.06 50% 1.97 1.88 25% 1.89 1.94 17 100% 1.63a .93a 50% 1.60ab .57b 25% 1.30b .16b 28 100% 2.13 .72 50% 2.15 .83 25% 2.09 .75 2Treatments were begun on day 3; stress relieved on day 29. yMean separation within time (day) and time (h) by LSD, 5% level. 35 Table 8. Growth rates for the control trees in the rapid water stress (RWS) and slow water stress (SWS) experiments. Growth parameter Growth rate2 (mm, cm, or no. day'l) Rapid Water Stress Experiment Leaf emergence 0.61 leaves Leaf group A 0.97 cm Leaf group B 0.99 cm Leaf group C 0.98 cm Shoot extension 1.35 cm Slow Water Stress Experiment Leaf emergence 0.50 leaves Leaf group A' 1.18 cm Leaf group B' 1.16 cm Leaf group C' 1.13 cm Shoot extension 1.35 cm Trunk diameter 0.055 mm 2Growth rates were determined from the average rate during the 10-12 day period of rapid leaf expansion. 36 Table 9. Growth and growth rates, expressed as percent of control, for the rapid water stress (RWS) trees at the end of the stress and recovery periods. Parameter End of Stress End of Recovery Cumultative Growth (% of control) Leaf emergence 73.3 80.3 Leaf Group A 61.6 77.7 Leaf Group B 5.0 77.2 Leaf Group C -- 103.3 Shoot extension 60.9 65.3 Growth Rates (% Of control) Leaf emergence 54.0 126.0 Leaf Group A 25.7 185.7 Leaf Group B 6.4 181.1 Leaf Group C -- -- Shoot extension 22.6 83.9 37 Table 10. Growth and growth rates, expressed as percent of control, slow water stress (SWS) for the trees (50 and 25% trts.) on the day responses were statistically different and at the end of the stress period. Day of Response End of Stress Parameter Treatment 50% 25% 50% 25% Cumulative Growth (% of Control) Leaf Emergence 58.3 49.6 Leaf Group A' 98.0 85.7 Leaf Group B' 82.5 74.9 Leaf Group C' 56.3 36.3 Shoot Extention 75.8 57.0 Trunk Diameter 64.2 38.7 Growth Rate (% of Control) Leaf Emergence 22.0 5.0 0.0 66.0 Leaf Group A' 43.3 56.7 43.3 56.7 Leaf Group B' 68.8 63.6 115.7 194.1 Leaf Group C' 40.0 3.3 67.2 61.7 Shoot Extension 51.9 62.6 33.3 20.0 Trunk Diameter 53.8 5.7 158.3 33.3 38 length to number of leaves (Table 11). For the RWS experiment, the estimated internode lengths were reduced by 19%. The internode lengths for the 50% treatment were unaffected, while those for the 25% treatment were reduced by 7%. The effect of water stress on shoot vs. trunk growth relationships was examined (Fig. 9). A change in the relationship was Observed. Discussion The effect Of water stress on the relationships among leaf emer- gence, leaf growth, shoot extension, and trunk expansion were illus- trated by this study. Internode length, estimated by the ratio of shoot length to number of leaves, was reduced as a result of the RWS treatment and the 25% SWS treatment. Water availability and leaf emergence rate were potential factors which controlled shoot and internode growth. A comparison of leaf emergence and shoot extension patterns for the SWS experiment suggested that shoot extension ceased as new leaves stopped emerging (Figs. 5 and 7). However, the percent reduction in shoot length was greater than the percent reduc- tion in leaf emergence for the RWS experiment and 25% SWS treatments (Table 8). Since cell expansion is dependent in part on turgor pres— sure (Hsiao 1973), water availability probably exhibited greater con- trol over shoot length and internode length than leaf emergence. The rapid phase of shoot growth began about three to four weeks before the rapid phase of trunk growth. A similar pattern was reported by Kozlowski (1958) and Khatamian and Hilton (1977). In the SWS experiment the relationship appeared to vary among treatments, 39 Table 11. Effect Of rapid water stress (RWS) and slow water stress (SWS) 0n the final shoot length to final leaf number ratio, and the treatment effects expressed as percent of control. Shoot 2 % of N0. of % of Shoot : Leaf % of Treatment Legggh Control LeavesZ Control (cm : Leaf) Control Rapid Water Stress Experiment Control 81.0 100 48.6 100 1.67 100 Stress 54.8 68 40.4 83 1.36 81 Slow Water Stress Experiment 100% 95.1 100 46.7 100 2.04 100 50% 80.2 84 39.3 84 2.04 100 25% 72.6 76 38.3 82 1.90 93 ZRepresents an average of four trees. 4O 40 E1 100% REPLACEMENT P. o 50% REPLACEMENT A 25% REPLACEMENT E U E? ii ,/’ ;; q‘f” 2 3‘ , (D Z LLJ ID" w “ C: u: A m D 2 H 2d “ 0 H -1 - * '54 U) l/ c, 1 r 1 T 1 1 -s o s 10 15 20 25 30 35 INCRERSE IN TCFl (MMZ) Figure 9. Increase in trunk cross-sectional area (TCA) vs. increase in shoot length of 'Redhaven' peach trees for three levels of water replacement 100, 50, and 25%. 41 indicating a change in the relationship between shoot and trunk growth as a result of the water stress (Fig. 9). This response was expected because trunk growth was shown to be more sensitive to water stress than shoot extension by the order of sensitivity and greater reduction in growth (Table 8), thus offsetting Unenormal shoot growth to trunk growth relationship. The RWS and SWS GXperiments had different effects on the growth and growth rates of peaches. In the RWS experiment, the number of newly emerged leaves was reduced immediately, while the leaf emergence rates were not significantly different until three days after the stress period began. A SWS also caused a reduction in leaf emergence, but these differences were not significant until after day 10. The RWS and the 25% treatment reduced shoot extension more than leaf emergence; whereas the opposite was observed for the 50% treatment, SWS for both cumulative growth and growth rates (Tables 8 and 9). An extended period of SWS was necessary before increases in shoot extension and shoot growth rates were reduced to the same extent as those under RWS. Regardless of the duration or severity of the stress,leaf growth was very sensitive to water stress, recovered quickly after rewatering and achieved 75-80% of the potential length even as water supplies slowly diminished. Stomata of 'Redhaven' peach leaves closed sooner under a rapid stress than a slow stress. In a similar experiment (Section II) stomatal conductance differed at 1100 and 1400b within three days after withholding water. After 11 days of the slow stress, neither morning or afternoon stomatal conductances differed; after 11 days of 42 the rapid stress, trees were watered to relieve the stress. Tan and Buttery (1982b) reported a similar decline in stomatal conductance after three days of stress, and reported that stomatal conductance was 80% of the control after only one-half of the root system had received water for three weeks. The stomatal sensitivity to stress observed in this study was similar to results obtained for field- grown trees (Cullinan and Weinberger 1932, Jones 1931, Xiloyannis et al. 1980). Stomata closed earlier in the day for the water stressed trees. Peach stomata appeared to be more sensitive to water stress than apple, which have been reported to remain Open under stress (Davies and Lakso 1979, Powell 1976). In addition to available water, other factors must be considered in analysis of cumulative growth and growth rates. Linear growth measurements provide only a general view of the performance of the tree; whereas dry weight measurements more accurately reflect photo- synthetic productivity (Causton and Hill 1981). The more rapid rates of leaf growth for the control trees of the SWS experiment (Table 8) were probably due to slightly warmer temperatures and increased radiation, since peach leaf growth rate was influenced by temperature and available radiation (Haun and Coston 1983). Diurnal changes in growth can lead to faulty measurements of real growth, if measurements are not made at similar times each time (Powell 1976, Klepper 1968, Kozlowski 1968). Even irregular timing of watering relative to measur- ing growth can lead to erroneous measurements of treatment effects. In the SWS experiment the rates of leaf emergence and trunk diameter 43 changes were affected after rewatering even with 50% or less of the water needed. In preliminary experiments with trunk diameter measure- ments using a linear transducer, small but measurable increases in trunk radius were detected within minutes after rewatering (unpub- lished results, M. E. Olien and J. A. Flore). Frequent manipulation of leaves and shoots for growth measurements may inflict damage and affect growth (Causton and Hill 1981); however, Haun and Coston (1983) have developed a scale for rating leaf emergence based on the "mor- phologic changes during leaf unfolding" which could minimize the physical damage. In temperate regions, the ability to reduce growth via water management may only be possible during droughty periods of consider- able length during DWII. Early wet periods are needed to establish good leaf area development. Exploiting the sensitivity of leaf emer- gence during this period may prove detrimental to the current crop. Adequate drought to reduce growth during DWII is most likely to occur if there is a period of excessive evaporative demand or if DWII is longer than the drought period. The duration of fresh weight stage II (FWII), which has been shown to be similar in length to DWII (Chalmers and Van Ende 1975), can vary 5-42 days depending on the season and variety (Tukey 1933). Therefore, this system may only work with long season varieties. Irrigation after harvest may be neglected for economical reasons; however, this may be advantageous time to irrigate for the benefit of trunk growth and carbohydrate storage if the current production has been low. 44 Scheduling irrigation according to trunk diameter changes is appealing. Trunk diameter changes are relatively easy to measure, the parameter is sensitive to water stress, and when expressed as trunk- cross-sectional area, it is an adequate measure of vigor for mature trees (Khatamian and Hilton 1977, Westwood and Roberts 1970). Further studies of the relationship of trunk growth to canopy growth, water stress development in the tree, the soil water conditions and the climatic conditions are necessary to determine the suitability of scheduling irrigation based on trunk diameter fluctuations. Conclusions Water stress reduced growth in 'Redhaven' peach trees. Two weeks of the SWS were required before a reduction in growth similar to the RWS was observed. Under RWS conditions, leaf emergence was more sensitive than leaf or shoot growth. Leaf growth rate for the RWS recovered fastest, while shoot growth rate recovered slowest. Under the SWS conditions, leaf emergence was more sensitive than leaf, trunk or shoot growth; however, leaf growth rate was more sensitive than leaf emergence, trunk growth, or shoot growth rate. Trunk growth was selected as the best parameter to monitor tree water status in research experiments for irrigation scheduling. Although leaf emergence and leaf growth rates were more sensitive, these parameters were not as suited to frequent and rapid sampling. Shoot growth did not appear sensitive enough. Trunk growth fluctua— tions were relatively easy to observe in the field, and the parameter was sensitive to water stress. Literature Cited Anonymous. 1982. "Fine tuning" sprinkler irrigation systems can result in better, bigger fruit crops.- The Good Fruit Grower 33(4): 6.7. Black, J.D.F., P.D. Mitchell and P.N. Newgreen. 1977. Optimum irri- gation rates for young trickle irrigated peach trees. Austr. J. Exp. Agr. An. Hus. 17:342-345. Causton, D.R. and J.C. Hill. 1981. The Biometry of Plant Growth. Edward Arnold (Publishers) L.T.D., London 307 pp. Chalmers, D.J. and B. van den Ende. 1975. Productivity of peach trees: factors affecting dry-weight distribution during growth. Ann. Bot. 39:423-32. Chalmers, D.J. and I.B. Wilson. 1978. Productivity of peach trees: tree growth and water stress in relation to fruit growth and assim- ilate demand. Ann. Bot. 42:285-294. Chalmers, D.J., K.A. Olson and T.R. Jones. 1983. Water relations of peach trees and orchards. IN: Water Deficits and Plant Growth Vol. 8: 197-232, Academic Press, Inc., New York. Childers, N.F. 1978. Modern Fruit Science Horticultural Publications, 8th Ed. New Jersey, pg. 330—337. Cullinan, F.P. and J.J. Weinberger. 1932. Studies on the influence of soil moisture on growth of fruit and stomatal behavior of 'Elberta' peaches. Proc. Amer. Soc. Hort. Sci. 29:28-33. Davies, F.S. and A.N. Lakso. 1978. Water relations in apple seed- lings: Changes in water potential components, abscissic acid levels and stomatal conductances under irrigated and non-irrigated conditions. J. Amer. Soc. Hort. Sci. 103(3): 310-313. Davies, F.S. and A.N. Lakso. 1979. Water stress responses of apple trees. I. Effects of light and soil preconditioning treatments on tree physiology. J. Amer. Soc. Hort. Sci. 104(3):392-395. Elfving, D.C. 1982. Crop responses to trickle irrigation. Hort. Rev. 4:1-48. 45 46 Haun, J.R. and D.C. Coston. 1983. Relationship of daily growth and development of peach leaves and fruit to environmental factors. J. Amer. Soc. Hort. Sci. 108(4): 666-671. Hendrickson, A.H. 1926. Certain water relations of the genus Prunus. Hilgardia. 1:479-524. Hsiao, T.C. 1973. Plant responses to water stress. Ann. Rev. Plant Physiol. 24:519-570. Khatamian, H. and R.J. Hilton. 1977. The relationship between shoot growth and area of trunk cross-section in several woody plant species. HortScience 12(3): 255-257. Klepper, B. 1968. Diurnal pattern of water potential in woody plants. Plant Physiol. 43:1931-1934. Kozlowski, T.T. 1968. Diurnal changes in diameters of fruits and tree stems of 'Montmorency' cherry. J. Hort. Sci. 43:1-15. Kramer, P.J. 1969. Plant and soil water relationships: a modern synthesis. McGraw-Hill Book Company, New York. pg. 365-368. Powell, 0.8.8. 1976. Continuous measurement of shoot extension and stem expansion in the field. J. Exp. Bot. 27:1361-1369. Proebsting, E.L. and J.E. Middleton. 1980. The behavior of peach and pear trees under extreme drought stress. J. Amer. Soc. Hort. Sci. 105(3): 380-385. Proebsting, E.L., J.E. Middleton and M.0. Mahan. 1981. Performance of bearing cherry and prune trees under very low irrigation rates. J. Amer. Soc. Hort. Sci. 106(2): 243-246. Scholander, P.F., H.F. Hammel, E.D. Bradstreet and E.A. Hemmingsen. 1965. Sap pressure in vascular plants. Science 148:339-346. Slavik, B. 1974. Methods of studying plant water relations. Springer-Verlga. New York. 449 pp. Stanley, C.D., B.K. Harbaugh and J.F. Price. 1983. Environmental factors influencing leaf water potential of Chrysanthemum. J. Amer. Soc. Hort. Sci. 108(2) 237-240. Steele, R.G.D. and J.H. Torrie. 1980. Principals and procedures of statistics. A biometrical approach. McGraw-Hill Book Company, Inc , N.Y. 633 pp. 47 Tan, C.S. and B. R. Buttery. 1982a. Response of stomatal conductance, transpiration, photosynthesis, and leaf water potential in peach seedlings to different watering regimes. Hort Science 17(2):222-223. Tan, C.S. and B.R. Buttery. 19826. The effect of soil moisture stress to various fractions of the root system on transpiration, photosynthesis and internal water relations of peach seedlings. J. Amer. Soc. Hort. Sci. 107(5):845-849. Tukey, H.B. 1933. Growth of the peach embryo in relation to growth Of fruit and season of ripening. Proc. Amer. SOC. Hort. Sci. 30:209- 217. Westwood, M.N. and A.N. Roberts. 1970. The relation between cross- sectional area and weight of apple trees. J. Amer. Soc. Hort. Sci. 95:28-30. Young, E., Hand, J.M. and S.C. Weist. 1981. Diurnal variation in water potential components and stomatal resistance in irrigated peach seedlings. J. Amer. Hort. Soc. Sci. 106(3): 337-340. Young, E., J.M. Hand and S.C. Weist. 1982. Osmotic adjustment and stomatal conductance in peach seedlings under severe water stress. Hort. Science 17(5):791-793. Xiloyannis, C., K. Uriu and G.C. Martin. 1980. Seasonal and diurnal variations in abscissic acid, water potential and diffusive resistance in leaves from irrigated and non-irrigated peach trees. J. Amer. Soc. Hort. Sci. 105(3): 412-415. SECTION II DIURNAL RESPONSES OF 'REDHAVEN' PEACH TREES UNDER WATER STRESS AND DURING RECOVERY 48 ABSTRACT Diurnal responses of 'Redhaven' peach trees (Prunus persica, L., Batsch) were observed during a two-week water stress period in a greenhouse environment. Late morning and afternoon stomatal conduc- tance and transpiration readings were lower for stressed plants during the stress period. Early morning stomatal conductance and transpira- tion readings differed after one week of the stress period. Leaf water potentials of stressed plants were at least 0.34MPa more nega- tive than those of nonstressed plants. Osmotic potentials of stressed trees were significantly less in early stages of stress, and turgor potentials varied only 0.12MPa during the stress period. Trunk diameters increased 5.5% for the stressed trees compared with 6.5% for the nonstressed trees. No treatment differences were observed after rewatering, indicating recovery from stress. 49 Introduction The diurnal variations in plant growth, water status, and stomatal functions are well documented for a variety of fruit trees (Chalmers et al. 1975, Davies and Lakso 1978, Goode and Higgs 1973, Klepper 1968, Xiloyannis et al. 1980, Young et al. 1981). Diurnal responses have been correlated with the following environmental factors: light, temperature, and humidity. Trunk diameter is at a maximum before sunrise and a minimum in the afternoon (Kozlowski 1968). Stomatal conductance reaches a maximum before noon and a minimum by midafter- nood (Davies and Lakso 1978, Young et al. 1981); whereas the peak in transpiration generally occurs aftermidday, when temperatures and vapor pressure deficits are the greatest (Kramer 1967). Similarly, plant water potential becomes most negative between 1000 and 1600b and least negative overnight (Klepper 1968, Young et al. 1981, Goode and Higgs 1973). Water flux in and out of the plant is the primary regu- lator of these diurnal curves; however, environmental factors and position in the canopy (Klepper 1968) can affect the extent and dura- tion of the change. The diurnal patterns observed for photosynthesis, stomatal con- ductance, leaf water potential, and limb shrinkage have been character- ized for several cultivars of peach under watered and stressed condi- tions (Chalmers 1975, 1983, Xiloyannis et al. 1980, Young et al. 1981). The use of one of these parameters in planning irrigation schedules 50 51 for peach would be desirable, and requires the characterization of the response to water stress. 'Redhaven' peaches are highly recom- mended for commercial planting in most peach producing areas in the United States (Childers 1978). The sensitivity of this cultivar to stress and its ability to recover after rewatering are important to planning the physiological aspects of scheduling. The objective of this research was to study the diurnal responses of these parameters: stomatal conductance, transpiration, leaf water potential, and trunk growth of 'Redhaven' peach trees during a cycle of water stress and recovery, and to assess their potential as indicators of water stress. Materials and Methods One-year-old peach trees, Prunus persica, L., cv. 'Redhaven'/ 'Halford', were potted in 19 liter containers in a soil mix of 2 soil:1 Sphagnum moss:1 sand (v:v:v), and were pruned to two branches. The trees were maintained in an open-ended quonset greenhouse which provided an outdoor environment protected from rain. Air temperature and relative humidity (Table 1) were similar to the prevailing condi- tions; however, the available photosynthetically active radiation (Table 1) was reduced to 60% of the available radiation. This level, 700-1000 pE m'z 5'1, was above saturation for 'Redhaven' peach leaf photosynthesis (Kappel et al. 1983) between 1000 and 1500h on most days. Stomatal conductance and transpiration were measured on the abaxial side of one recently expanded leaf from each branch on each tree four times per day with a steady state porometer (Licor Inc., 52 Table 1. Air temperature (°C), relative humidity (RH, %), and available photosynthetically active radiation (PAR, uE m-2 s‘l) values recorded at the time of the stomatal conductance measurements Time of Day (hr) Date ‘Parameterz 0800 1100 1400 1700 June 8 Temp. 24.8 32.8 32.2 R.H. 49.0 31.5 30.4 PAR 657 908 855 June 11 Temp. 21.8 25.9 29.9 28.9 R.H. 43.7 32.8 28.1 29.4 PAR 626 819 998 548 June 17 Temp. 18.0 23.5 29.3 26.4 R.H. 50.1 39.8 33.5 38.7 PAR 381 837 938 238 June 21 Temp. 19.0 22.2 25.9 26.4 R.H. 56.3 48.5 37.3 34.7 PAR 436 711 754 705 June 29 Temp. 22.8 24.8 28.5 25.7 R.H. 72.7 59.9 46.1 48.2 PAR 259 727 440 135 2Each value represents the mean of 32 measurements. 53 Model 1600). These same leaves were used for leaf water potential measurements. Total leaf water potential was determined two times per day with a pressure bomb (PMS, Corvalis, Oregon) according to the technique of Scholander et al. (1965). The leaves were then sealed in airtight bags and frozen to -20°C for later osmotic potential measurements, which were determined by dewpoint hygrometry (Wescor, Inc., C-52 Chambers and HR-T33 microvoltmeter) (Slavik 1974). Trunk diameters were determined with a millimeter micrometer (Mitutoyo Instruments, Model 193-101, range 0-2510.01mm). Samples for soil moisture were taken at the end of the day and the percent water deter- mined gravimetrically (Slavik 1974). A soil moisture release curve, relating soil water content to soil water potential was determined by recording soil water content at a series of applied pressures (Richards 1947). At field capacity, the soil contained 20% water by weight (soil water potential = 2 kPa) and at wilting contained 13% water (soil water potential = 100 kPa) (Fig. 1). Water stress was induced by withholding water until wilting occurred. The stress period began on June 8 and ended on June 26. The control trees were watered to field capacity every two to three days. The experiment was arranged as a randomized complete block with eight replications per treatment. Blocks were arranged by trunk diameter size. Measurements were determined on June 8, 11, 17, 21, and 29, 1982. At least significant difference (LDS) statistic (P = 0.05) was used to determine statistical differences between treatments for all parameters except trunk diameters, which was not analyzed (Steele and Torrie 1980). 54 .~w>w_ Nm .omn An cowpncnamm new: .pcmewcmgxm any mcwnnn mncmsnnmcp wmwgum nnn Focucou mo Anmxv cowmcwn Loon; Fwow nan Conn; Fwom pcmugoa .H mgnmwd 55 (9:90 NOISNEJ. 108 can T. 00—... on: 1 ON1 Ow... wb(O an wzaq pa azaq bu wzafi m U m U m U m 1 m u m 1 U 1 I U mmwuhm um dO¢hZOU uU In 0 (OZH x) aanismw 1105 n— ON 56 Results Leaf water potential of the stressed leaves was always more negative than the control leaves on the dates tested (Fig. 2). Sig- nificant differences existed on June 17 and 21 at 0800 and 1400h. The effects of water stress on 0800h osmotic and turgor potentials appeared as differences in osmotic potential on June 11 and 17, and as differences in turgor potential on June 17 and 21 (Table 2). Treat- ment effects were not detected after rewatering for leaf water poten- tial. Stomatal conductance decreased between 0800 and 1100 h for both treatments (Fig. 3, a-e); 1400h stomatal conductances were always less than the 1000h values. Midday differences in stomatal conductance existed on June 11, 17, and 21. Differences between treatments at 0800 and 1700h occurred on June 17 and 21 when drought was the most severe. After rewatering all trees responded similarly. Transpiration rates (Table 3) were significantly reduced for the stressed trees between 1000 and 1400h on June 11, and between 0800 and 1700h on June 17 and 21. The amplitude of the diurnal variation of transpiration rate was less in the trees under stress. No differences between treatments were observed after rewatering. Trunk growth occurred in all trees; however, the increase in growth of the stressed trees was 5.5% compared with 6.5% for the con- trol trees (Fig. 4). Normal late afternoon trunk expansion appeared to begin sooner for the stress trees, even after rewatering. 57 .Fw>w_ Rm .omn an cowpmgnamm can: .coonH ncw oowo an mm>mmF comma _:w>m;nmm. mo Anazv anocmpoa Lopez CGGF no Acm>oowx ncn mmwcnm Lona; Co pomGWM .N mgzmwm 58 an mzan «a mzan .3 m2:.. p p mzan a uzan WEB all-I'll- qulIIIJ filllllllu all. «Illa £94. :30 t can :39 Sun Sun \bEuu Eco 4.43am Eon m2; .4. _ T. A Ti- .4» _ _ _ .I l 0.“: 3 V .3 * m o A I. 3 H ... . ...d x a a. O . “a a O m... N s 4 1 4..- u a V 1 J N.Y. m 01.0 335 m1 *II... 405.200 0 a . L OOPS 59 Table 2. Effect of water stress on the 0800b osmotic, turgor, and total leaf water potential (MPa) of 'Redhaven' peach Dates Treatment June 8 June 11 June 17 June 21 Osmotic Potential (MPa)Z Control -3.01 -2.75 a -2.85 -2.98 Stress -2.93 -2.89 b -3.07 -3.01 Turgor Potential (MPa)Z Control 1.44 1.34 1.77 a 1.61 a Stress 1.41 1.37 1.37 b 1.29 b Total Leaf Water Potential (MPa)Z Control -1.58 -1.41 -1.08 a -1.38 a Stress -1.51 -1.52 -1.70 b -1.72 b ZValues followed by different letters are statistically differ- ent (LSD, 5% level). 60 Figure 3.a-e. Effect of water stress and recovery on the diurnal Changes in stomatal conductance (cm sec-1) of 'Redhaven' peach leaves. Mean separation by LSD, 5% level. June 8, 1982 June 11, 1982 June 17, 1982 June 21, 1982 June 29, 1982 (DQOU’DJ STOMRTRL CONDUCTRNCE (CM/SEC) 0.9 .1 1 0.7 0.5 61 .4 1:1 CONTROL 0 STRESS fi T I T I I T 400 600 800 1000 1200 1400 1600 1800 TIME OF DRY (HOUR) June 8, 1982 2000 STOMHTHL CONDUCTRNCE (CM/SEC) 0.9 2.1 .9 1 1-1 0.7 0.5 62 - E] CXDNTFKN. Q) SHTUESS 400 r 600 T 800 1600 1500 1100 TIME OF DRY (HOUR) June 11, 1982 1 1600 1 1800 2000 STOMHTHL CONDUCTRNCE (CH/SEC) 1.6 63 1.4 ED CKNVTRCM. (D STRESS 0.0 400 I 600 1 800 1600 1500 1400 TIME OF DRY (HOUR) June 17, 1982 1 1600 r 1800 2000 STOMHTRL-CONDUCTHNCE (CM/SEC) 64 2.3 2.1 1.9 L 1-7 1 1 L, I. 0.? <9 STRESS 400 1 600 T 800 1000 1200 1400 TIME or DRY (HOUR) June 21, 1982 1 1600 1 1800 2000 STOMRTRL CONDUCTRNCE (CM/SEC) 65 2.3 0.7 400 1 600 1 800 1600 1500 1100 TIME OF CRY (HOUR) June 29, 1982 1 1600 1 1800 2000 66 Table 3. Effect of water stress and recovery op)the diurnal Changes in transpiration rate (pg H20 mm'2 s' of 'Redhaven' peach leaves. Transpiration Rate (ug H20 mm'Z 5'1)Z Date Treatment Time (hr) 0800 1100 1400 1700 June 8 Control 26.49 33.5 20.3 Stress 26.93 39.81 19.59 June 11 Control 23.0 27.22a 31.34a 24.95 Stress 21.9 22.74b 22.89b 20.99 June 17 Control 5.95a 10.15a 8.50a 11.6a Stress 3.05b 3.45b 2.0b 4.16b June 21 Control 24.2a 36.12a 36.41a 34.8a Stress 18.31b 30.1b 27.64b 23.62b June 29 Control 8.31 28.88 29.39 22.98 Stress 12.31 27.57 29.05 20.94 ZMean separation within date and time by LSD, 5% level. 67 .maanp nonaa .na>nnnam. Co Amsev npzonm nnnnp any no >na>oaan nnn amanum Lana: we paawwm .n annmwa O? 9' «v 0' V? a? 0? an uza. Z aza. 2 aza. 2 aza. 2.3 . 1|] .IIIIIII. al.-III... 1.IIIIIIJ 58 so: can Ea: can so: can so: as: ._ _ _ _ _ n _ _ */ J OIIIIIIIIO. 1. “I... /* “X“ In J AV 0\ L *1... .6528 1 h? (zmm) VSUV ‘IVNOllGBS-SSOHO )IINflHJ. 68 Discussion Osmotic adjustment has been demonstrated in stressed apple trees (Davies and Lakso 1979, Goode and Higgs 1973), and it has been pro- posed for peach trees (Young et al. 1982). The water potential data (Table 2) implied that osmotic adjustment may be a factor in moderating turgor loss in stressed peach trees. In the early stages of stress, the stressed trees had significantly less negative osmotic poten- tials and the calculated turgor potentials varied only 0.12 MPa during the stress period. Similar results were obtained for 'Redhaven' peach in an earlier experiment (Sec. 1). Verification of this mechanism would require more frequent sampling of total water and osmotic poten- tial under stressed and nonstressed conditions. It has been suggested that determination of osmotic potential by the tissue-freezing method should be calibrated against the pressure volume curve (Brown and Tanner 1983). Errors associated with freezing and thawing of the leaf tissue may lead to overestimating the potential for osmotic adjustment (Brown and Tanner 1983). The stomatal responses observed agreed with other published data on peach stomatal behavior. The diurnal pattern was similar to field results (Xiloyannis et al. 1980) and measurements of stomatal aperature (Hendrickson 1926). The effects of increasing evaporative demand, created by the interactive effects of temperature and humidity, was believed to be largely responsible for changes in stomatal conductance and transpiration rate observed throughout the day. The statistical analysis of the stomatal conductance (Fig. 3), transpiration (Table 3), 69 and the stomatal conductance data reported earlier (Sec. 1) indicated that I‘Redhaven' peach stomata were responsive to mild stress condi- tions even though leaf water potential did not differ and the percent of available soil water was above 50%. This response to a mild stress was viewed as part of a mechanism to conserve water and stabilize the plant water status. Recovery in response to rewatering is dependent upon the duration and severity of the water stress imposed (Ludlow et al. 1980) and may be related to an adaptive mechanism. Leaf water potentials have recov- ered to prestress levels within 24 hours of rewatering (Ludlow et al. 1980, Tan and Buttery 1982b); however, stomatal conductance required one to five days (Hsiao 1973, Tan and Buttery 1982b, Ludlow et al. 1980), and was less than 100% of the prestress values. The recovery results presented here were obtained three days after rewatering and are in agreement with those reported previously (Tan and Buttery 1982b). Stomatal conductances for peaches subjected to a slowly pro- gressing stress (Sec. I) were not different from the well-watered con- trol 24 hours after rewatering. Adaptation via preconditioning probably occurred as the stress progressed and perhaps eliminated the "after effect" (Hsiao 1973) of reduced stomatal conductance. Davies and Lakso (1979), Tan and Buttery (1982b), and unpublished results on 'Montmorency' cherry (M. E. Olien and J. A. Flore) have demonstrated that stomatal conductance was greater and the ability to tolerate subsequent drought periods was improved for trees precondi- tioned to water stress. The potential for preconditioning could be expected for 'Redhaven' peach trees. 70 Conclusion This study illustrated some of the adaptive responses of 'Red- haven' peach trees experiencing water stress. Under mild stress, stomatal conductance declined earlier and osmotic adjustment appeared to have a role. These mechanisms moderated the potential for water loss and aided in maintaining turgor. The ability to recover from water stress was indicated by the lack of statistical differences between treatments for stomatal conductance and leaf water potential. Literature Cited Brown, P.W. and C. B. Tanner. 1983. Alfalfa osmotic potential: a comparison of the water-release curve and frozen-tissue methods. Agron. J. 75:91-93. Chalmers, D.J. and I.B. Wilson. 1978. Productivity of peach trees: tree growth and water stree in relation to fruit growth and assimilate demand. Ann. Bot. 42:285-294. Chalmers, D.J., K.A. Olson and T.R. Jones. 1983. Water relations of peach trees and orchards. In: Water Deficits and Plant Growth Vol. 8: 197-232, Academic Press, Inc., New York. Childers, N.F. 1978. Modern Fruit Science Horticultural Publications, 8th Ed. New Jersey, p. 330-337. Davies, F.S. and A.N. Lakso. 1978. Water relations in apple seedlings: Changes in water potential components, abscissic acid levels and stomatal conductances under irrigated and non-irrigated conditions. J. Amer. Soc. Hort. Sci. 103(3):310-313. Davies, F.S. and A.N. Lakso. 1979a. Water stress responses of apple trees. I. Effects of light and soil preconditioning treatments on tree physiology. J. Amer. Soc. Hort. Sci. 104(3):392-395. Davies, F.S. and A.N. Lakso. 1979b. Diurnal and seasonal changes in leaf water components and elastic prOperties in response to water stress in apple trees. Physiol. Plant. 46:109-114. Hendrickson, A.H. 1926. Certain water relations of the genus Prunus. Hilgardia 1:479-524. Hsiao, T.C. 1973. Plant responses to water stress. Ann. Rev. Plant Physiol. 24:519-570. Hsiao, T.C., E. Acevedo, and D.W. Henderson. 1976. Stress metabolism, water stress, growth and osmotic adjustment. Phil. Trans. Royal Soc. London, series B, 273:479-500. Klepper, B. 1968. Diurnal pattern of water potential in woody plants. Plant Physiol. 43:1931-1934. Kozlowski, T.T. 1968. Diurnal changes in diameters of fruits and tree stems of 'Monmorency' cherry. J. Hort. Sci. 43:1-15. 71 72 Kramer, P.J.. 1969. Plant and soil water relationships: a modern synthesis. McGraw-Hill Book Company, New York. p. 365-368. Landsberg, J.J. and H.G. Jones. 1981. Apple Orchards. In: Water Deficits and Plant Growth T.T. Kozlowski, ed. Vol. 6: 419-469. Ludlow, M.M., T.T. Ng and C.W. Ford. 1980. Recovery after water stress of leaf gas exchange in Panicum maximum var. trichoglume Austr. J. Plant Physiol. 7:299-313. Richards, L.A. 1947. Pressure membrane apparatus, construction and use. Agr. Engin. 28:451-454. Scholander, P.F., H.F. Hammel, E.D. Bradstreet and E.A. Hemingsen. 1965. Sap pressure in vascular plants. Science 148:339-346. Slavik, B. 1974. Methods of studying plant water relations. Springer-Verlag. New York. 449pp. Tan, C.S. and Buttery, B.R. 1982a. Response of stomatal conductance, transpiration, photosynthesis and leaf water potential in peach seedlings to different watering regimes. HortScience I7(2):222-223. Tan, C.S. and B.R. Buttery. 1982b. The effect of soil moisture stress to various fractions of the root system on transpiration, photosynthesis and internal water relations of peach seedlings. J. Amer. Soc. Hort. Sci. 107(5):845-849. Young, E., Hand, J.M. and S.C. Weist. 1981. Diurnal variation in water potential components and stomatal resistance in irrigated peach seedlings. J. Amer. Soc. Hort. Sci. 106(3):337-340. Young, E., J.M. Hand and S.C. Weist. 1982. Osmotic adjustment and stomatal conductance in peach seedlings under severe water stress. HortScience 17(5):791-793. Xiloyannis, C., K. Uriu and G.C. Martin. 1980. Seasonal and diurnal variations in abscissic acid, water potential and diffusive resistance in leaves from irrigated and non-irrigated peach trees. J. Amer. Soc. Hort. Sci. 105(3):412-415. SUMMARY 73 Summary Water stress reduced growth in 'Redhaven‘ peach trees. Two weeks of the SWS were required before a reduction in growth similar to the RWS was observed. Under RWS conditions, leaf emergence was more sensitive than leaf or shoot growth. Leaf growth rate for the RWS recovered fastest, while shoot growth rate recovered slowest. Under the SWS conditions, leaf emergence was more sensitive than leaf, trunk, or shoot growth; however, leaf growth rate was more sensitive than leaf emergence, trunk growth, or shoot growth rate. Trunk growth was selected as the best parameter to monitor tree water status in research eXperiments for irrigation scheduling. Although leaf emergence and leaf growth rates were more sensitive, these parameters were not as suited to frequent and rapid sampling. Shoot growth did not appear sensitive enough. Trunk growth fluctua- tions were relatively easy to observe in the field, and the parameter was sensitive to water stress. This study illustrated some of the adaptive responses of 'Red- haven' peach trees experiencing water stress. 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