Combined effects of drought and high temperature on water relations of wheat and sorghum

Drought and high temperature are major factors limiting crop production. The two stresses occur together in many regions, but they usually are investigated separately. This study tested the hypothesis that high temperature interacts with drought to affect water relations, and the effect is greater in heat-sensitive wheat (Triticum aestivum L.) than in sorghum (Sorghum bicolor L. Moench). Wheat and sorghum were grown in soil that was well watered or not watered in controlled chambers at 15/10, 25/20, 35/30 and 40/35 °C day/night. Soil water content (SWC), leaf relative water content (RWC), leaf water potential (), leaf osmotic potential (), leaf turgor potential (P) and osmotic adjustment (OA) were determined at 2-d intervals. All values held nearly constant at all temperatures when soil was well watered but were affected strongly by high temperature when water was withheld. The combined stresses reduced SWC, RWC, Psi and , and unevenly raised P over time, particularly in sorghum. Sorghum also exhibited marked OA at high temperature, which was usually lethal to wheat. High temperature appeared to interact with drought to affect water relations by altering SWC and not by influencing OA. The results demonstrated that crops maintain nearly stable water relations regardless of temperature when moisture is ample, but high temperature strongly affects water relations when water is limiting. Increasing the thermotolerance of wheat might improve its potential to acclimate to both high temperature and drought.     

Osmotic and specific ion effects on the germination of Prosopis strombulifera

BACKGROUND AND AIMS: Salinity can affect germination of seeds either by creating osmotic potentials that prevent water uptake or by toxic effects of specific ions. Most studies have only used monosaline solutions, although these limit the extent to which one can interpret the results or relate them to field conditions. The aim of this work was to evaluate the germination of Prosopis strombulifera seeds under increasing salinity by using the most abundant salts in central Argentina in monosaline or bisaline iso-osmotic solutions, or in solutions of mannitol and polyethylene glycol. METHODS: Seeds were allowed to germinate under controlled conditions in a germination chamber at 30 +/- 1 degrees C and at 80 % r.h. Salinizing agents were KCl, NaCl, Na(2)SO(4), K(2)SO(4), NaCl + Na(2)SO(4) and KCl + K(2)SO(4) and osmotic agents were polyethylene glycol 6000 and mannitol. Treatments for all osmotica consisted of 0.0, -0.4, -0.8, -1.2, -1.5, -1.9 and -2.2 MPa solutions. KEY RESULTS: The percentage of germination decreased as salinity increased. SO(4)(2-) in monosaline solutions, with osmotic potentials -1.2 MPa and lower, was more inhibitory than Cl(-) at iso-osmotic concentrations. This SO(4)(2-) toxicity was alleviated in salt mixtures and was more noticeable in higher concentrations. K(+) was more inhibitory than Na(+) independently of the accompanying anion. CONCLUSIONS: Different responses to different compositions of iso-osmotic salt solutions and to both osmotic agents indicate specific ionic effects. This study demonstrates that the germination of P. strombulifera is strongly influenced by the nature of the ions in the salt solutions and their interactions. Comparative studies of Cl(-) and SO(4)(2-) effects and the interaction between SO(4)(2-) and Cl(-) in salt mixtures indicate that extrapolation of results obtained with monosaline solutions in the laboratory to field conditions can be speculative.     

The effect of potassium application on leaf water relations characteristics of field grown barley plants (Hordeum distichum L.)

Leaf water relations characteristics were studied in spring barley fertilized at low (50 kg ha^-1) or high (200 kg ha^-1) levels of potassium applied as KCl. The leaf water relations characteristics were determined by the pressure volume (PV) technique.Seasonal analysis in fully irrigated plants showed that within 2 weeks from leaf emergence the leaf osmotic potential at full turgor ( ¹⁰⁰) decreased from about –0.9 to –1.6 MPa in leaf No 7 (counting the first leaf to emerge as number one) and from about –1.1 to –1.9 MPa in leaf No 8 (the flag leaf) due to solute accumulation. ¹⁰⁰ was 0.05 to 0.10 MPa lower in high K than in low K plants. Thus, an ontogenetically determined accumulation of solutes occurred in the leaves independent of K application. The ratio of leaf weight at full turgor to dry weight (TW/DW) decreased from about 5.5 in leaf No 6 to 4.5 in leaf No 7 and 3.8 in leaf No. 8. The TW/DW ratio was 4 to 10% higher in high K than in low K plants indicating larger leaf cell size in the former. The tissue modulus of elasticity () was increased in high K plants. The main effect of high K application on water relations was an increase in leaf water content and a slight decrease in leaf During drought limited osmotic adjustment and increase in elasticity of the leaf tissue mediated turgor maintenance. These effects were only slightly modified by high potassium application.     

水盐梯度下荒漠植物多样性格局及其与土壤环境的关系

植物多样性格局作为生物多样性维持的一个重要方面可揭示群落构建的信息,反映物种对环境的适应性。结合样带调查和实验分析的方法,研究新疆艾比湖湿地自然保护区内水盐梯度下荒漠植物多样性格局及其与土壤环境因子间关系。结果表明:(1)高、低水盐样地(SW1,SW2)土壤容积含水量(SVWC)和电导率(EC)分别为16.65%和12.02 m S/cm及2.63%和1.91m S/cm,水盐变化主要影响草本和部分灌木群落的植物组成;(2)高水盐生境下植物群落无明显趋势性分布,低水盐生境下植物种依水盐和营养元素呈区域性分布。(3)高水盐生境下荒漠植物的多度分布呈对数正态模型,低水盐条件下符合Zipf模型,多度分布的变化反映了群落组成结构的水盐梯度响应;(4)SW1样地多样性总体显著高于SW2样地,土壤p H、SVWC和硫(S)对植物多样性有不同程度的极显著影响。综上可知,荒漠植物分布及多样性格局与土壤环境间关系呈一定的水盐梯度响应规律,本研究可为该地区植被恢复和土壤盐渍化治理提供科学依据。     

内蒙古高原荒漠区几种锦鸡儿属(Caragana)优势植物的生理生态适应特性

比较了内蒙古高原荒漠区4种锦鸡儿属(Caragana)优势植物——柠条锦鸡儿、狭叶锦鸡儿、垫状锦鸡儿和荒漠锦鸡儿的生理适应特性。研究发现:4种锦鸡儿属植物中,荒漠锦鸡儿的叶片含水量、束缚水/自由水比值、水势以及水分利用效率最低,气孔导度日变化表现为与气温变化相似的早晚低、中午高的单峰曲线。4种锦鸡儿蒸腾速率日变化状况相似,均在10:00达到最大,以后逐渐降低,但日蒸腾积累值垫状锦鸡儿<荒漠锦鸡儿<柠条锦鸡儿<狭叶锦鸡儿。相比较,柠条锦鸡儿、狭叶锦鸡儿和垫状锦鸡儿对当地的水分条件有良好的适应性,能够保持较好的水分状况,水分亏缺在15%以下,而荒漠锦鸡儿叶水分亏缺日变幅较大,保水能力不及其它3种。渗透调节比较研究发现:荒漠锦鸡儿的渗透势最低,细胞质离子浓度最高,无机渗透调节物产生的渗透势所占的比例也更大,说明其低渗透势的维持主要来自无机渗透调节物质的较多积累。保护酶和自由基比较研究发现:POD和SOD活性荒漠锦鸡儿明显高于其它3个种,但CAT活性在4种植物中无显著差别;叶片自由基含量狭叶锦鸡儿>荒漠锦鸡儿>柠条锦鸡儿>垫状锦鸡儿。这些结果表明:(1)荒漠锦鸡儿对干旱环境的适应方式与其它3种不同,柠条锦鸡儿、狭叶锦鸡儿和垫状锦鸡儿以强保水能力、维持稳定的水分而适应,而荒漠锦鸡儿以更负的渗透势、更高细胞质离子浓度弥补其更多的水分消耗和对水分变化的强耐性而适应,较高的保护酶活性可能是其强耐性的生理基础之一。(2)保水能力弱的锦鸡儿种主要通过无机离子的积累,调节细胞质渗透势,保持水分平衡,这是一种相对节省能量的适应对策。     

Chloroplast volume: cell water potential relationships and acclimation of photosynthesis to leaf water deficits

Studies were undertaken to determine if there is an association between nonstomatally-mediated acclimation of photosynthesis to low water potential (w) and the maintenance of chloroplast volume during water stress. Spinach plants either kept well watered throughout their growth (non-acclimated), or subjected to water stress such that leaf w dropped to -1.5 megapascals (MPa) and then were rewatered (acclimated) were subjected to drought episodes. During these stress periods, photosynthesis was maintained to a greater extent in acclimated plants as compared to non-acclimated plants at w below -1 MPa.Estimates of internal leaf [CO₂] suggested that photosynthetic acclimation to low w was not primarily due to altered stomatal response. As w dropped from initial values, a decline in steady state levels of ribulose 1,5-bisphosphate (RuBP) occurred in both non-acclimated and acclimated plants. RuBP decline was less severe in acclimated plants.Low w effects on chloroplast volume in non-acclimated and acclimated plants were estimated by measuring the volume of intact chloroplasts isolated from plants in solutions which were made isotonic to declining leaf osmotic potential during the drought episodes. Chloroplast volume was maintained to a greater extent at low w in acclimated, as compared with non-acclimated plants. Although substantial osmotic adjustment occurred in both non-acclimated and acclimated plants, the extent of osmotic adjustment was the same. These data were interpreted as supporting the hypothesis that cellular-level acclimation to low w is associated with chloroplast volume maintenance, and this physiological acclimation is correlated with enhanced photosynthetic capacity of the leaf at low w.Abbreviations [CO₂]_i internal leaf CO₂ concentration - s osmotic potential - RWC relative water content - RuBP ribulose 1,5-bisphosphate - w water potential     

西鄂尔多斯地区强旱生小灌木的水分参数

应用PV技术研究了西鄂尔多斯地区绵刺、红沙、四合木和霸王柴4种超旱生灌木的水分关系参数膨压(ψ_P)、细胞弹性模量(ε)、细胞体积比(RCV)及其相互关系.结果表明：在4种荒漠旱生灌木中,红沙保持最大膨压的能力最强(a=2.4593).不同荒漠旱生灌木保持膨压的方式不同：绵刺通过弹性调节保持膨压(ε_max=8.4005 MPa);红沙通过渗透调节来保持膨压(ψ_π100=-3.1302 MPa;ψ₀=-3.5074 MPa);四合木通过渗透调节和弹性调节的协同作用来维持膨压;霸王柴通过渗透调节来保持膨压,而弹性调节能力较弱.绵刺具有柔软而高弹性的细胞壁,是构成其根茎系统快速吸收和传导水分能力的因素之一.四合木具有较柔软而高弹性的细胞壁且ψ_P的变化随RCV减小而趋于缓慢,说明四合木具有较强的持水能力和抗脱水能力.     

Water relations and osmotic adjustment in Lycopersicon esculentum and L. pennellii during short-term salt exposure and recovery

Cultivated tomato Lycopersicon esculentum (L.) Mill. cv. P-73 and its wild salt-tolerant relative L. pennellii (Correll) D'Arcy accession PE-47 growing on silica sand in a growth chamber were exposed to 0, 70, 140 and 210 m M NaCl nutrient solutions 35 days after sowing. The saline treatments were imposed for 4 days, after which the plants were rinsed with distilled water. Salinity in L. esculentum reduced leaf area and leaf and shoot dry weights. The reductions were more pronounced when sodium chloride was removed from the root medium. Reduction in leaf area and weight in L. pennellii was only observed after the recovery period. In both genotypes salinity induced a progressive reduction in leaf water potential and leaf conductance. During the recovery period leaf water potential (ψ₁) and leaf conductance (g₁) reached levels similar to those of control plants in wild and cultivated species, respectively. Leaf osmotic potential at full turgor (ψ_os) decreased in the salt treated plants of both genotypes, whereas the bulk modulus of elasticity was not affected by salinity. Leaf water potential at turgor loss point (ψ_tlp) and relative water content at turgor loss point (RWC_tlp) appeared to be controlled by leaf osmotic potential at full turgor (ψ_os) and by bulk modulus of elasticity, respectively. At lowest salinity, the wild species carried out the osmotic adjustment based almost exclusively on Cl⁻ and Na⁺, with a marked energy savings. Under highest salinity, this species accommodate the stress through a higher expenditure of energy due to the contribution of organic solutes to the osmotic adjustment. The domesticated species carried out the osmotic adjustment based always on an important contribution of organic solutes.     

Seasonal changes of osmotic pressure, symplasmic water content and tissue elasticity in the blades of dune grasses growing in situ along the coast of Oregon

Abstract Midday water potentials of blades of the dune grasses Ammophila arenaria (L.) Link and Elymus mollis Trin. ex Spreng. growing in situ declined over the summer growing period, indicating a trend of increasing water stress. An analysis of the water relations characteristics of these blades using pressure-volume techniques demonstrated that both species increased bulk osmotic pressure at full hydration () and, therefore, bulk turgor as an acclimation response. In A. arenaria, however, the increase of osmotic pressure (+ 0.35 MPa) was entirely the result of decreasing symplasmic water content. The increase of osmotic pressure (+ 0.54 MPa) observed in E. mollis blades was due to solute accumulation (72% of Δ) and to a lesser degree, decreased symplasmic water content (28% of Δ). Osmotic adjustment in E. mollis blades was accompanied by a significant decrease in tissue elasticity (_max went from 12 to 19 MPa). The elastic properties of A. arenaria blades remained constant over the same period and had a maximum modulus (10 MPa) that was always less than that of E. mollis, As estimated from Höfler plots, these seasonal adjustments of osmotic pressure and differences in tissue elasticity enabled plants in situ to maintain turgor pressure in the range of 0.5–0.6 MPa at the lowest water potentials of mid-August. Laboratorygrown plants exhibited the species-specific differences in osmotic pressure, turgor pressure, and tissue elasticity observed in field plants. Although certain alterations of leaf structure were expected to coincide with the observed changes and species-specific differences in symplasmic water content and tissue elasticity, these could not be detected by measurements of specific leaf weight or the ratio of dry matter to saturated water content.     

Photosynthesis of six barley genotypes as affected by water stress

The effect of water stress on plant water status and net photosynthetic gas exchange (PN) in six barley genotypes (Hordeum vulgare L.) differing in productivity and drought tolerance was studied in a controlled growth chamber. Osmotic adjustment (OA), PN, stomatal conductance (gs), and the ratio intercellular/ambient. CO2 concentration (Ci/Ca) were evaluated at four different levels of soil water availability, corresponding to 75, 35, 25 and 15 % of total available water. Variability in OA capacity was observed between genotypes: the drought tolerant genotypes Albacete and Alpha showed higher OA than drought susceptible genotypes Express and Mogador. The genotype Albacete exhibited also higher PN than the others at low water potential (Ψ). The ratios of PN/gs and Ci/Ca showed that differences in photosynthetic inhibition between genotypes at low Ψ were probably due to nonstomatal effects. In Tichedrett, a landrace genotype with a very extensive root development, OA was not observed, however, it exhibited a capacity to maintain its photosynthetic activity under water stress. This revised version was published online in June 2006 with corrections to the Cover Date.     

Changes at panicle emergence in the water relations of a wetland and a dryland Japonica rice cultivar under wetland conditions

The diurnal and seasonal changes in plant water relations of two Japonica rice ( Oryza sativa L.) cultivars, Nipponbare and Tachiminori, were studied under flooded conditions at Kyoto University. The dryland cv. Tachiminori maintained higher predawn and midday leaf osmotic potentials relative to the wetland cv. Nipponbare during the vegetative stage, but the ranking was reversed after flowering. The relationship between leaf water potential and leaf osmotic potential showed that prior to panicle emergence Nipponbare was able to adjust osmotically to maintain turgor, whereas after heading there was little turgor maintenance. Tachiminori showed little difference in osmotic adjustment before and after panicle emergence. Fertilizer treatment during panicle development also helped to maintain the degree of osmotic adjustment in both cultivars.     

Salt tolerance in Aster tripolium L. II. Ionic regulation

Abstract Measurements of tissue ion contents (Na, K and Cl) were carried out at frequent intervals on plants of Aster tripolium L. grown at a range of salinities for 36 d. Aster tripolium behaved as a typical halophyte showing high levels of inorganic ion accumulation even at low salinities. As salinity increased Na replaced K to a large extent in the shoot but root K was unaffected up to 500 mol m^?3 external NaCl. Shoot (Na + K) concentration on a tissue water basis was maintained constant in all treatments throughout the experiment, whereas shoot (Na + K) on a dry weight basis showed marked fluctuations in some treatments. An increase in (Na + K) per gram dry weight was, however, accompanied by a parallel increase in fresh weight: dry weight (FW : DW) ratio. Transport of (Na + K) to the shoot per unit root weight changed during the experiment in the manner expected, given the observed changes in shoot relative growth rate and FW : DW to result in a constant shoot (Na + K) concentration on a water basis. Chloride was the major balancing anion in the shoot at high salinity, but never accounted for more than 38% of the (Na + K) found in the root tissue. At all salinities (Na + K) salts accounted for the majority of the measured shoot sap osmotic potential. The interactions between salinity, growth, ion transport and osmotic adjustment are discussed.     

Dendroecology of Prosopis flexuosa woodlands in the Monte desert: Implications for their management

In the Monte desert of Argentina open woodlands of several species of Prosopis occur in areas with accessible underground water. The great latitudinal extent of the Monte (26–43°S) exhibits strong climatic gradients involving temperature, rainfall seasonality, and wind regime. Prosopis woodlands have been a source of subsistence for human communities for several centuries and continue to be exploited by the local inhabitants. The “mining” of this resource has led to severe desertification and consequent impoverishment of the local people. In order to suggest strategies for the better management and recuperation of these woodlands we studied the population structure and productivity of Prosopis flexuosa from multiple plots at Pipanaco (27°58′S), Telteca (32°20′S), and Ñacuñán (34°03′S). For each plot we measured the density of P. flexuosa trees, number of stems, basal diameter (DAB), height and canopy diameter of each tree. Tree ring data were used to determine the growth rates, annual wood production and biological rotation age for each area. The ecological structure of the woodlands differs between the three sites. Along this north–south transect, there is a decrease in adult tree density, mean basal diameter, mean tree height, canopy cover, productivity and total wood biomass. Consequently, the potential sustainable use of these woodlands varies. Only the northern, Pipanaco, woodlands have the potential for lumber production. In contrast, the short, multi-stem and low-productivity trees in the Telteca and Ñacuñán areas can only sustain a combination of local firewood production and activities such as extensive grazing by livestock. The present, uniform regulations for harvesting wood in these areas must be changed to acknowledge these differences in order to optimize wood production in, and conservation of, these woodlands.     

Contribution of osmotic adjustment to the dehydration tolerance of water-stressed pigeon pea (Cajanus cajan (L.) millsp.) leaves

Abstract Water-stressed pigeonpea leaves have high levels of osmotic adjustment at low leaf water potentials. The possible contribution of this adjustment of dehydration tolerance of leaves was examined in plants grown in a controlled environment. Osmotic adjustment was varied by withholding water from plants growing in differing amounts of soil, which resulted in different rates of decline of leaf water potential. The level of osmotic adjustment was inversely related to leaf water potential in all treatments. In addition, at any particular water potential, plants that had experienced a rapid development of stress exhibited less osmotic adjustment than plants that experienced a slower development of stress. Leaves with different levels of osmotic adjustment died at water potentials between –3.4 and –6.3 MPa, but all leaves died at a similar relative water content (32%). Consequently, leaves died when relative water content reached a lethal value, rather than when a lethal leaf water potential was reached. Osmotic adjustment delayed the time and lowered the leaf water potential when the lethal relative water content occurred, because it helped maintain higher relative water contents at low leaf water potentials. The consequences of osmotic adjustment for leaf survival in water-stressed pigeonpea are discussed.     

小麦叶片光合作用与其渗透调节能力的关系

在缓慢干旱条件下,小麦叶片渗透调节能力在一定范围内随胁迫程度的加剧而增加,而在快速干旱下,渗透调节能力丧失。小麦叶片通过渗透调节使光合速率和气孔导度对水分胁迫的敏感性降低,叶片维持较高的电子传递能力、RuBP羧化酶活性和叶绿体光合能量转换系统活性,并推迟了小麦叶片光合速率受气孔因素限制向叶肉细胞光合活性限制转变的时间。     

土壤含水量对麻疯树幼苗生长及其生理生化特征的影响

以麻疯树(Jatropha curcas L.)1年生盆栽幼苗为材料,通过设置3个土壤水分(分别为80%、50%和30%田间持水量(FC))处理,研究土壤含水量对麻疯树幼苗生长及生理生化指标的影响,探讨麻疯树的水分适应性。结果表明:随土壤含水量的降低,麻疯树的株高、生物量等均呈下降趋势,根重比、根冠比和比叶面积无显著变化;蒸腾速率和气孔导度显著降低,净光合速率和PSII的光能转换效率无明显变化;叶片色素含量显著升高。在80%FC下,丙二醛和过氧化氢含量、可溶性糖和游离脯氨酸含量、超氧化物歧化酶活性和抗坏血酸含量均呈现最大值。在本实验条件下:麻疯树作为一种抗旱性较强的树种,30%FC没有对其造成干旱胁迫;而从生理生化代谢方面看,80%FC不能为麻疯树生长提供最适宜的条件,主要体现在体内自由基积累、膜脂过氧化程度加重以及叶绿体色素含量的降低,但体内抗氧化防御系统的积极防御和渗透调节物质含量的增加缓解了水分过多对麻疯树造成的伤害,从而没有对净光合速率造成影响。因此,在当地土壤养分状况下,以30%-50%FC的土壤含水量栽培,更有利于麻疯树的生长。     

Contrasting physiological responses of six eucalyptus species to water deficit

BACKGROUND AND AIMS: The genus Eucalyptus occupies a broad ecological range, forming the dominant canopy in many Australian ecosystems. Many Eucalyptus species are renowned for tolerance to aridity, yet inter-specific variation in physiological traits, particularly water relations parameters, contributing to this tolerance is weakly characterized only in a limited taxonomic range. The study tests the hypothesis that differences in the distribution of Eucalyptus species is related to cellular water relations. METHODS: Six eucalypt species originating from (1) contrasting environments for aridity and (2) diverse taxonomic groups were grown in pots and subjected to the effects of water deficit over a 10-week period. Water potential, relative water content and osmotic parameters were analysed by using pressure-volume curves and related to gas exchange, photosynthesis and biomass. KEY RESULTS: The six eucalypt species differed in response to water deficit. Most significantly, species from high rainfall environments (E. obliqua, E. rubida) and the phreatophyte (E. camaldulensis) had lower osmotic potential under water deficit via accumulation of cellular osmotica (osmotic adjustment). In contrast, species from low rainfall environments (E. cladocalyx, E. polyanthemos and E. tricarpa) had lower osmotic potential through a combination of both constitutive solutes and osmotic adjustment, combined with reductions in leaf water content. CONCLUSIONS: It is demonstrated that osmotic adjustment is a common response to water deficit in six eucalypt species. In addition, significant inter-specific variation in osmotic potential correlates with species distribution in environments where water is scarce. This provides a physiological explanation for aridity tolerance and emphasizes the need to identify osmolytes that accumulate under stress in the genus Eucalyptus.