玉米对渗透胁迫的反应和生理适应

利用不同渗透势的培养液模拟土壤干旱条件,研究了玉米杂交种“中单2号”在此条件下的生长和生理的变化。实验表明,各指标对于渗透胁迫的变化敏感性顺序为叶片延伸速率、叶水势、脯氨酸含量>净光合速率>相对透性。玉米幼苗在渗透胁迫下具有一定的生理适应能力,表现在一定的渗透胁迫范围内随胁迫时间的延长,生长、生理变化有趋于缓和或恢复的趋势。     

土壤干旱对沙棘苗木生长及水分利用的影响

研究了土壤干旱条件下盆栽沙棘苗木生长、光合和水分关系的变化。结果表明,同样环境条件下,蒸腾速率随干旱胁迫程度加重而降低,而蒸腾日进程差异不大,均为单峰曲线,峰值出现在11：00;轻、中度干旱胁迫下沙棘叶含水量、水势、渗透势、膨压下降幅度较小,光合速率、侧枝生长速率保持在较高水平,能维持基本的生长量,表现出耐旱植物的生理特征;重度干旱胁迫使上述指标下降较显著,且长时间胁迫后,33．3％沙棘幼苗死亡。     

水分胁迫对春播玉米苗期生长及其生理生化特性的影响

采用盆栽试验,以‘蠡玉18'玉米单交种为供试材料,设置充分供水(CK)、轻度水分胁迫(LS)、中度水分胁迫(MS)和重度水分胁迫(SS)4个水分处理水平,研究了水分胁迫对春播玉米苗期保护酶活性和生长的影响,以探讨土壤水分胁迫对玉米苗期生长发育及其生理过程的影响机制.结果表明:(1)随着水分胁迫程度的加剧,玉米幼苗的生物量显著下降,根冠比、根系活力和脯氨酸含量增加,且水分胁迫对玉米幼苗地上部生物量的抑制作用更大;可溶性蛋白含量差异不明显,MDA含量波动变化.(2)随着水分胁迫时间的延长,根冠比、根系活力和植株脯氨酸含量先升高后降低,可溶性蛋白含量呈先下降后升高的趋势;玉米幼苗叶片和根系MDA积累波动变化,而叶片MDA含量始终高于根系.(3)在水分胁迫初期,玉米叶片中CAT活性较SOD、POD响应更敏感;玉米苗期根系在中度水分胁迫下主要依赖CAT来降低氧化危害,而在重度水分胁迫下前期主要依赖CAT、后期通过CAT和POD的共同作用来降低氧化伤害;水分胁迫条件下,叶片和根系POD同步降低氧化伤害,而SOD和CAT在叶片和根系间存在互补作用.研究表明,在不同程度的水分胁迫条件下,玉米幼苗的生长受到一定程度的抑制,但其能够通过调节自身的保护酶活性和渗透调节物质含量来减轻干旱伤害,维持植株的正常生理代谢功能.     

水分胁迫对玉米苗期生理和形态特性的影响

水分胁迫下3个玉米品种苗期形态和生理特征变化的研究结果表明,在中度水分胁迫下,鲁单981、赤单202和郑单958三个品种在株高、茎粗、叶片数和叶面积等形态指标方面变化不大,与正常供水下生长的玉米几个参数基本一致,而重度水分胁迫下,鲁单981的株高、茎粗和总叶面积均小于赤单202和郑单958.测定结果还表明鲁单981的光合速率和蒸腾速率受水分胁迫的影响最大,而郑单958和赤单202受到的影响相对较小;水分胁迫在一定程度上能够提高玉米的水分利用效率,增幅与品种关系较大,抗旱型品种增幅明显,耗水型品种增幅相对较少.     

盐胁迫对不同品种玉米苗期生长与叶片光合特性的影响

为研究盐胁迫对不同玉米品种玉米苗期生理性状的影响, 以玉米杂交种隆平206、秦龙14以及隆平206亲本(母本L239和父本L7221)为试验材料, 设置不同盐浓度处理, 分析玉米苗期生长与叶片光合特性的变化。结果表明, 盐胁迫下玉米植株高和地上部分鲜重显著下降, 随着盐浓度的增加, 其下降幅度增加; 两杂交种品种比较, 盐胁迫对秦龙14的影响较隆平206大; 隆平206两亲本比较, 盐胁迫对父本L7221较母本L239植株高与地上部分鲜重的影响更大。与对照相比, 盐胁迫显著增加玉米叶片色素含量, 且随着盐浓度的增加, 其增幅逐渐增加。盐胁迫显著增加叶片净光合速率, 但单叶光合速率逐渐降低, 两杂交种品种表现一致。可见虽然盐胁迫下单叶光合速率下降, 单位面积叶片的光合作用对玉米有一定的补偿作用。盐胁迫对秦龙14单叶光合速率的影响较隆平206大, 隆平206两亲本比较, 盐胁迫对父本L7221的影响较母本L239更大。     

镉胁迫对西瓜幼苗生长及其叶片解剖结构和生理特性的影响

该研究以‘北抗1号’西瓜幼苗为试验材料,采用实验室盆栽方法,考察在不同浓度镉胁迫(0、60、120、180和240 mg/L)处理下西瓜幼苗的生长及其叶片生理特性和解剖结构的变化特征,初步探讨西瓜耐受镉胁迫的生理机制。结果显示：(1)在镉胁迫条件下,西瓜幼苗的生长受到抑制,随着镉胁迫浓度的增加,西瓜幼苗的叶片形态黄化现象逐渐加重,根系形态逐渐纤弱,株高、茎粗、茎节数和叶片数均呈现下降趋势。(2)镉胁迫下,西瓜幼苗叶片主脉中细胞受损,主脉直径显著减小,叶肉组织疏密度显著降低。(3)随着镉胁迫浓度的升高,西瓜幼苗的含水量、净光合速率、SOD活性等显著降低,丙二醛和游离脯氨酸含量显著升高,POD活性和可溶性蛋白含量先升高后降低,生理特性受到显著影响。研究发现,‘北抗1号’西瓜幼苗对镉有一定的适应性,在低浓度(60 mg/L)镉胁迫处理下,西瓜幼苗的形态特征、生理特性变化不显著,但在高浓度(180 mg/L)镉胁迫下,幼苗的生长受到严重抑制,渗透调节系统以及生物膜保护系统严重受损。     

复合外源物质对玉米幼苗抗寒性的影响

该研究采用不同浓度的水杨酸(SA)、脱落酸(ABA)、磷酸二氢钾(KH2PO4)以及抗坏血酸(VC)进行正交组合获得不同浓度组合的复合外源物质,同时以蒸馏水处理作为对照,将其喷施于玉米幼苗后进行低温胁迫处理,在胁迫结束后使幼苗恢复生长,并测定叶片相关生长指标及生理生化指标的变化。结果表明:(1)与对照组相比,9种复合外源物质处理均可显著提高玉米幼苗的相对生长速率、干物质积累速率及脯氨酸含量,降低相对电导率,总体上提高了玉米幼苗的素质。(2)在4℃低温胁迫下,9种复合外源物质处理下幼苗相对生长速率、干物质积累速率、根系活力、脯氨酸含量、可溶性蛋白含量及可溶性糖含量,均显著高于对照,并减缓了丙二醛的积累和相应的膜脂过氧化,降低了相对电导率,提高了玉米幼苗的耐冷性。低温胁迫条件下,水杨酸、脱落酸、磷酸二氢钾和抗坏血酸四种物质组成的复合物可以提高玉米幼苗的耐冷性,其中以SA0.14 g·L~(-1)+ABA 0.015 g·L~(-1)+KH_2PO_4 3.0 g·L~(-1)+V_C 3.0 g·L~(-1)的复合物效果最好。该研究结果为新型复合抗寒剂的应用推广提供了技术支持。     

模拟岩溶旱钙土壤基质中AM真菌对玉米幼苗光合生长的影响

利用盆栽试验,探讨了AM真菌在模拟岩溶区干旱、高钙及其双重胁迫的土壤基质中对玉米幼苗光合生长的影响。结果表明:玉米幼苗的菌根侵染率在不同处理下的大小顺序为对照干旱双重胁迫高钙。无论接种与否,干旱、高钙及其双重胁迫均导致玉米幼苗生物量、净光合速率下降。未接种AM真菌条件下,玉米幼苗生物量在干旱、高钙及其双重胁迫下较对照分别低3.2%、63.7%、76.0%,净光合速率较对照分别低33.4%、86.9%、98.8%;接种AM真菌条件下,玉米幼苗生物量在干旱、高钙及其双重胁迫下较对照分别低16.3%、78.4%、80.2%,净光合速率较对照分别低9.7%、92.8%、91.7%。与同种条件下的非菌根植株相比,干旱及双重胁迫下的菌根植株生物量、叶绿素含量、光合蒸腾速率、最大光化学效率,以及P吸收均呈上升趋势;高钙胁迫下的菌根植株叶绿素含量、最大光化学效率有所增加,但生物量、光合蒸腾速率以及N、P的吸收未体现菌根促进效应。AM真菌与干旱及双重胁迫的交互作用对玉米幼苗的净光合速率影响显著,与高钙交互作用对玉米幼苗净光合速率无显著影响。AM真菌能够通过促进玉米幼苗N、P吸收及叶绿素含量增加,光化学效率、气孔导度增大,从而提高玉米幼苗光合作用能力促进生长。实验结果对岩溶生态系统中合理利用菌根技术及制定合理的农业生产措施具有重要的理论和实践意义。     

不同生育期玉米叶片光合特性及水分利用效率对水分胁迫的响应

利用大型移动防雨棚开展了玉米水分胁迫及复水试验,通过分析玉米叶片光合数据,揭示了不同生育期水分胁迫及复水对玉米光合特性及水分利用效率的影响。结果表明:水分胁迫导致玉米叶片整体光合速率、蒸腾速率和气孔导度下降以及光合速率日变化的峰值提前;水分胁迫后的玉米叶片蒸腾速率、光合速率和气孔导度为适应干旱缺水均较对照显著下降,从而提高了水分利用效率,缩小了与水分充足条件下玉米叶片的水分利用效率差值;在中度和重度水分胁迫条件下,玉米叶片的水分利用效率降幅低于光合速率、蒸腾速率和气孔导度的降幅, 有时甚至高于正常供水条件下的水分利用效率;适度的水分胁迫能提高玉米叶片的水分利用效率,从而增强叶片对水分的利用能力,抵御干旱的逆境;水分亏缺对玉米光合速率、蒸腾速率及水分利用效率的影响具有较明显滞后效应,干旱后复水,光合作用受抑制仍然持续;水分胁迫时间越长、胁迫程度越重,叶片的光合作用越呈不可逆性;拔节-吐丝期水分胁迫对玉米叶片光合作用的逆制比三叶-拔节期更难恢复。     

沼液施用对干旱胁迫下玉米幼苗生长和生理特性的影响*

为了探明干旱胁迫下沼液对玉米幼苗抗旱、光合生理、形态的缓解效应,以中度抗旱玉米杂交种‘先玉335’和较强抗旱杂交种‘中单2号’为材料,采用10%聚乙二醇-6000模拟干旱胁迫,研究50%沼液根部浇灌处理对干旱胁迫下玉米幼苗生长和生理特性的影响。结果表明,沼液根部施用可以显著提高两品种玉米的抗旱性,有效缓解干旱胁迫对玉米幼苗根系和地上部生长的抑制作用,促进两品种玉米幼苗生长和提高根系活力,降低根冠比,且‘先玉335’的变幅更大;同时显著提高两品种叶片SOD、POD和CAT活性以及可溶性糖、脯氨酸、可溶性蛋白含量(‘中单2号’的CAT除外),降低MAD含量,且对‘中单2号’的影响更显著;沼液根施还可以显著提高干旱胁迫下两品种叶片的净光合速率(Pn)、蒸腾速率(Tr),降低气孔导度(Gs)、胞间CO_(2)浓度(Ci),但‘中单2号’的Tr和Gs除外,同时使两品种叶片叶绿素含量和水分利用效率(WUE)均显著增加。可见,沼液根施处理可以有效改善干旱胁迫下玉米幼苗的光合能力,显著提高幼苗抗氧化酶活性和渗透调节物质的含量,减轻膜脂过氧化程度,有效缓解干旱胁迫对2种不同抗旱性玉米幼苗的生长抑制,从而增强玉米耐受干旱胁迫的能力,且对‘中单2号’的缓解效果更明显。     

干旱胁迫与复水对块根紫金牛生理特性的影响

以岩溶特有药用植物块根紫金牛为试材,研究土壤水分胁迫及复水条件下其叶片光合参数、相对含水量、质膜透性、渗透调节物质含量的变化特性。结果表明:水分胁迫下,块根紫金牛的叶片净光合速率、气孔导度和蒸腾速率均几乎接近零点,但胞间CO2浓度上升,即非气孔因素限制是光合速率下降的主要原因。水分胁迫不影响块根紫金牛单位面积的总叶绿素和类胡萝卜素含量,但干旱处理的Chl a/b和Car/Chl分别显著低于和高于对照。水分胁迫下,块根紫金牛的叶片相对含水量、相对电导率和丙二醛含量显著增大,即膜系统受到一定的伤害;块根紫金牛叶片脯氨酸含量显著降低,可溶性蛋白含量无显著变化,可溶性糖含量显著增大,但增大幅度不大,说明其在干旱胁迫下的渗透调节能力较弱。复水处理后,块根紫金牛全部指标均能恢复到对照水平,说明其对干旱胁迫较为敏感,主要采取避旱策略。     

Hydraulic regulation strategies for whole-plant water balance of two maize inbred lines differing in drought resistance under short-term osmotic stress

The conservation of water in agriculture requires an understanding of the mechanisms of plant–water relations. This study aimed to reveal hydraulic regulation strategies of maize (Zea mays L.) for maintaining the plant water balance during drought. The water relations of two maize inbred lines (Tian4 and 478) that differ in their resistance to drought in the field were investigated under well-watered conditions and osmotic stress induced with 10 % PEG 6000. The leaf transpiration rate and leaf water potential of 478 varied diurnally, but remained constant in Tian4, which is more drought resistant. Tian4 plants showed morphological, anatomical and physiological advantages that protected them from foliar water loss. The strategies of leaf hydraulics to regulate leaf water balance during the day and during short-term osmotic stress also differed between Tian4 and 478. The leaf hydraulic conductivity of Tian4 and 478 increased temporarily, but their root hydraulic conductivities were reduced under osmotic stress. However, the root hydraulic conductivity of Tian4 subsequently recovered. Lower and rapidly reduced leaf transpiration and the ability of root hydraulics to recover from short-term osmotic stress can help explain the strategies for plant water balance of drought-tolerant maize.     

The Comparative Drought Resistance of Landraces of Sorghum and Millet From Dry and Humid Regions

It may be that land-races of sorghum (Sorghum sp.) and millet[Pennisetum americanum (L.) Leeke] which evolved along geographicalgradients of rainfall in Africa and India, differ in their droughtresistance. Any physiological attributes found to be correlatedwith low rainfall might be important and effective characteristicsfor crop production in dry regions. Twenty land-races were chosen which evolved along geographicalgradients of rainfall, seven millets from India, six sorghumsfrom Mali, and seven sorghums from the Sudan. Races were evaluatedfor their growth potential and plant water relations under hydroponicsconditions in a growth chamber. A water stress treatment wasimposed by adding polyethylene glycol-8000 to the nutrient solution,giving a solute water potential of -0.5 MPa, compared with acontrol solution at 003 MPa. Drought resistance, in terms of relatively less growth inhibitionunder stress, was higher in races from dry regions than in racesfrom humid regions. Of all the physiological variables measured[carbon exchange rate, (CER), transpiration, transpiration ratio(CER/transpiration), leaf diffusive resistance, leaf water potentialand osmotic adjustment], only osmotic adjustment under stresswas generally correlated with average rainfall at each race'sorigin, indicating greater osmotic adjustment in land-racesfrom drier regions. Races with a greater capacity for osmoticadjustment were characterized by smaller plants with high ratesof transpiration and low rates of leaf senescence under stress. The carbon exchange rate per unit leaf area increased as liveleaf area decreased under stress due to leaf senescence. Thus,drought resistant races under stress tended to have lower CERper unit live leaf area (but not per plant) than susceptibleraces. Transpiration ratios under stress were lower in resistantthan in susceptible races, mainly because resistant races hadhigher transpiration. The results for the measured variables showed a general trendfor greater drought resistance in sorghum than in millet, indicatingthat the commonly observed adapation of the millets to dry environmentsmay be due to other factors, such as drought escape or heattolerance. Sorghum sp. Pennisetum americanum L. (Leeke), water stress, osmotic adjustment, photosynthesis, transpiration, evolution, drought resistance     

Role of Osmotic Potential Gradients during Water Stress and Leaf Senescence in Fragaria virginiana

The physiological basis underlying differences in sensitivity of different aged leaves to water stress was investigated in Fragaria virginiana Duchesne. Differential susceptibility of only older leaves to water stress in the field during summer months appeared related to gradients in leaf osmotic potential within the plant and by an age dependency in the ability of leaves to adjust osmotically when challenged by periodic water deficits. Under greenhouse conditions, older leaves senesced invariably during an imposed water stress while control leaves of comparable age and stressed younger leaves remained green. Osmotic potentials of intermediate aged and younger leaves became approximately 1 to 2 bars lower after a single cycle of imposed stress and up to 10 bars lower after two cycles of stress. Pronounced gradients in leaf osmotic potential within individual whole plants were observed following two cycles of water stress that were significantly different from control values. Osmotic adjustment was dependent on leaf age with the greatest capacity for adjustment in the intermediate aged leaves. Loss of osmotic adjustment was rapid upon rewatering with a half-life of 4 days. An irreversible component of adjustment was observed, amounting to about 10% (or 2 bars) of the maximally adjusted state. This irreversible component could be accounted for in part by significant changes in cell size and other anatomical alterations in the leaf that affect cellular osmotic volume, and, hence, cellular water relations.     

不同耐盐性花生品种对NaCl胁迫的光合和抗逆生理响应特征

以较耐盐花生品种‘花育25’、‘鲁花12’和盐敏感品种‘海花1’、‘花育20’为材料,采用盆栽试验,设置0、1.0、2.0、3.0 g/kg土壤NaCl胁迫浓度梯度,测定其净光合速率、表观量子效率、气孔导度等光合特性,以及抗氧化酶活性和渗透调节物质含量等指标,明确NaCl胁迫条件下不同耐盐性花生品种光合和生理生化特性的适应特征。结果表明：(1)NaCl胁迫明显抑制各品种花生叶片光合作用,净光合速率随盐胁迫浓度的升高呈明显降低的趋势。(2)各品种花生叶片净光合速率均先随光照强度的增强而升高,当光强达到一定数值时趋于平稳;光补偿点和光饱点因品种和盐胁迫浓度差异较大,较高的盐胁迫浓度使叶片光补偿点升高,盐敏感品种的光饱和点降低。(3)盐胁迫条件下,各品种叶片表观量子效率和最大净光合速率均随盐胁迫强度的增加呈显著降低趋势,盐敏感品种利用弱光的能力在低盐胁迫下强于耐盐品种,其最大净光合速率在较高盐胁迫浓度(3.0 g/kg)下明显低于耐盐品种,但两类品种的叶片表观量子效率降幅相近(78.65%~88.00%)。(4)在NaCl胁迫下,耐盐品种叶片自由水含量显著高于盐敏感品种;在2.0～3.0 g/kg NaCl胁迫下,耐盐品种叶片SOD、CAT、POD活性和MDA含量的升降幅度均低于盐敏感品种;耐盐品种在NaCl浓度低于2.0 g/kg时的抗氧化能力明显高于盐敏感品种。研究发现,盐胁迫下花生品种抗盐耐逆的主要生理响应特征是提高光补偿点和最大净光合速率,增强叶片持水能力和物质代谢能力,以及提升抗氧化和渗透调节能力。     

Optimized potassium nutrition improves plant-water-relations of barley under PEG-induced osmotic stress

Aims

Water use efficiency (WUE) of crop plants is an important plant trait for maintaining high yield in water limited areas. By influencing osmoregulation of plants, potassium (K) plays a critical role in stress avoidance and adaptation. However, whole plant physiological mechanisms modulated by K supply in respect of plant drought tolerance and water use efficiency are not well understood. In the present study, growth, development and transpiration dynamics of two barley cultivars were evaluated with and without PEG-induced osmotic stress using an automated balance system and image based leaf area determination.

Methods

Experiments were conducted to study the effects of varied K supply under different osmotic stress treatments on a wide range of morphological, biochemical and physiological characteristics of barley plants such as leaf area development, daily whole plant transpiration rate (DTR), stomatal conductance (g_s), assimilation rate (A_N), biomass and leaf water use efficiency (WUE) as well as foliar abscisic acid (ABA) concentrations. Two barley cultivars (cv. Sahin-91 and cv. Milford) were treated with two K supply levels (0.04 and 0.8 mM K) and osmotic stress induced by polyethylene glycol 6000 (PEG) for a period of 9 days (in total 48 days experiment) in the hydroponic plant culture (non-PEG and + 20% PEG ).

Results

Without PEG, low-K supply depressed dry matter (DM) by almost 60% averaged across both cultivars. Under osmotic stress (+PEG), total leaf area was reduced by almost 70% in low-K compared to adequate-K plants. Low K concentration under PEG stress was correlated with higher ABA concentration and was correlated with lower leaf- and whole plant transpiration rate. Biomass-WUE under low K supply decreased significantly in both barley cultivars, to a greater extent in cv. Milford under osmotic stress. However, leaf-WUE was not affected by K supply in the absence of osmotic stress.

Conclusions

It was suggested that reduced biomass-WUE in low-K treated barley plants was not related to inefficient stomatal control under K deficiency, but instead due to reduced assimilation rate. It was further hypothesized that under low K supply, a number of energy consuming activities reduce biomass-WUE, which are not distinguished by measuring leaf-WUE. This study showed that low K supply under osmotic stress increases foliar ABA concentration thereby decreasing plant transpiration.

     

High CO2 levels reduce ethylene production in kiwifruit

We examined the roles of turgor potential and osmotic adjustment in plant growth by comparing the growth of spring wheat ( Triticum aestivum cv. Siete cerrors) and sudangrass ( Sorghum vulgare var. Piper) seedlings in response to soil water and temperature stresses. The rates of leaf area expansion, leaf water potential and osmotic potential were measured at combinations of 5 soil water potentials ranging from −0.03 to −0.25 MPa and 6 soil temperatures ranging from 14 to 36°C. Spring wheat exhibited little osmotic adjustment while sudangrass exhibited a high degree of osmotic adjustment. However, the rate of leaf area growth for sudangrass was more sensitive to water stress than that of spring wheat. These results were used to evaluate the relationship between growth and turgor potential. The modified Arrhenius equation based on thermodynamic considerations of the growth process was evaluated. This equation obtains growth rate as a function of activation energy, enthalpy difference between active and inactive states of enzymes, base growth rate and optimum temperature. Analyses indicate that the modified Arrhenius equation is consistent with the Lockhart equation with a metabolically controlled cell wall extensibility.     

A proteomics approach for identifying osmotic-stress-related proteins in rice

Osmotic stress can endanger the survival of plants. To investigate the mechanisms of how plants respond to osmotic stress, rice protein profiles from mannitol-treated plants, were monitored using a proteomics approach. Two-week-old rice seedlings were treated with 400mM mannitol for 48h. After separation of proteins from the basal part of leaf sheaths by two-dimensional polyacrylamide gel electrophoresis, 327 proteins were detected. The levels of 12 proteins increased and the levels of three proteins decreased with increasing concentration or duration, of mannitol treatment. Levels of a heat shock protein and a dnaK-type molecular chaperone were reduced under osmotic, cold, salt and drought stresses, and ABA treatment, whereas a 26S proteasome regulatory subunit was found to be responsive only to osmotic stress. Furthermore, proteins whose accumulation was sensitive to osmotic stress are present in an osmotic-tolerant cultivar. These results indicate that specific proteins expressed in the basal part of rice leaf sheaths show a coordinated response to cope with osmotic stress.     

Effects of Increasing Water Stress on Simulated Swards of Festuca arundinacea Schreb under Wind Tunnel Conditions

The effects of increasing water stress on water relations, leafconductance, leaf extension and leaf rolling of Festuca arundinaceain sward (I m²) were investigated under wind tunnel conditions.The plants were grown in a container 60 cm deep and the experimentwas conducted over a 36 d period. Upon cessation of watering(day 11), leaf extension and conductance were affected. Within8 d, the onset of leaf rolling helped to reduce transpirationand to maintain leaf water potential. Nocturnal recovery of turgor potential helped in maintainingleaf extension at a moderate level and in the final 5 d waterand osmotic potentials dropped sharply as leaf rolling becamemore acute and leaf extension stopped. The grass combines various morphological and physiological mechanismsto prevent water losses and maintain growth. Festuca arundinacea, tall fescue, wind tunnel, water stress, water potential, osmotic potential, conductance, leaf rolling, leaf extension