短期干旱对水稻叶水势、光合作用及干物质分配的影响

采用盆栽水分试验,研究了不同生育期短期干旱处理对水稻叶水势、光合作用和干物质分配的影响．结果表明,干旱胁迫后,水稻叶水势低于对照,午后叶水势回升缓慢。凌晨叶水势随土壤含水量的降低而降低,表现为阈值反应。叶片净光合速率与凌晨叶水势密切相关,低于凌晨叶水势临界值,水稻叶片净光合速率急剧下降在水稻抽穗期和灌浆期叶片净光合速率显著下降的凌晨叶水势临界值为-1.04和-1．13MPa,对应的土壤含水量阈值分别为饱和含水量的61.0％和50．9％,土壤水势分别为-0．133和-0．240MPa干旱胁迫下单叶净光合速率的日变化规律表现为：胁迫较轻时,单叶净光合速率在正午附近出现低谷;胁迫严重时,净光合速率全天低于对照,且不及对照的一半。短期干旱后,水稻叶、根、穗的分配指数均降低,茎鞘的分配指数升高。本研究可为水稻节水灌溉管理和水分限制下水稻的生长模拟提供生理基础和理论依据。     

干旱胁迫对霸王水分生理特征及细胞膜透性的影响

以2年生霸王为试验材料,用盆栽人工控制土壤水分,研究不同梯度土壤水分条件对霸王水分生理特征、丙二醛含量和细胞膜相对透性的影响.结果表明,与充足供水对照(土壤重量含水量为23%)相比,在严重干旱胁迫(土壤含水量为3%)20 d和45 d时,霸王叶水势和叶片相对含水量分别显著降低70.87%和45.54%、26.81%和12.66%;相应的叶片MDA含量和细胞膜相对透性分别显著增加33.81%和21.78%、17.51%和14.98%;严重干旱胁迫30 d使得霸王叶片保水力显著下降;同时随着土壤干旱胁迫程度的增强,霸王日蒸腾耗水量持续下降,且严重干旱胁迫处理的蒸腾耗水量日变化为水平直线型,其余处理均为单峰型.研究发现,严重干旱胁迫下随着胁迫时间的延长,霸王叶水势和叶片相对含水量有增加趋势,而叶片MDA含量和细胞膜相对透性则有减小趋势,它能够通过自身的调节机制,逐渐改善叶片水分状况,降低细胞膜伤害程度,从而适应严重干旱环境.     

夏玉米苗期主要生长指标的土壤水分临界点确定方法

土壤水分不足是引起作物干旱的最主要因素。准确确定作物响应土壤水分的临界点对客观辨识、监测作物干旱的发生发展具有重要意义。本研究基于6个初始土壤水分的夏玉米持续干旱模拟试验,利用多元方差分析确定了较早响应土壤水分变化的玉米生长指标,并提出了基于正态总体统计容忍下限确定引起各指标发生显著性变化的临界土壤湿度的方法。结果表明:夏玉米苗期茎含水率、叶含水率、蒸腾速率、光合速率、气孔导度和叶面积较早响应土壤水分,其临界土壤水分(0~30 cm平均土壤相对湿度)分别为72%、65%、62%、60%、58%、46%,反映出随着土壤水分降低、干旱发生发展,玉米的茎含水率、叶含水率、蒸腾速率、光合速率、气孔导度和叶面积会依次受到影响。研究结果可为夏玉米苗期干旱发生发展的监测和定量评估提供依据,也为生态系统响应阈值的确定提供了思路。     

几种作物的生理指标对土壤水分变动的阈值反应

 在生长盛期,谷子、高梁、冬小麦的气孔导度、叶水势和光合速率在一定土壤含水量范围内并不随着土壤含水量的降低而发生明显变化,只有当土壤含水量低于一定程度时,才随着土壤湿度的降低而减少,表现为对土壤水分有明显的阈值反应。不同作物此阈值下限存在差异,高粱在大于田间持水量42％～45％的根层土壤湿度条件下,气孔阻力和叶水势基本维持恒定;谷子的这个指标在50％左右,冬小麦在60％左右。而夏玉米在所试土壤湿度范围内(20％～30％土壤体积含水量),气孔阻力和叶水势基本维持不变,而光合作用随着土壤含水量的增高而出现增加趋势。表明在这4种作物中,只有玉米需要充足的水分供应才能维持其良好的生长发育,而高粱具有比其它3种作物更强的适应土壤水分变动能力,从而比其它作物更抗旱和耐旱。     

春小麦对骤旱的响应特征及其阈值分析

与缓慢发展的干旱过程不同,骤旱具有发生速度快,短期内可致害的特点。目前,关于作物骤旱致害的临界阈值及其调控机制尚不清楚。以春小麦为供试作物,通过桶栽试验,模拟研究骤旱过程中小麦受旱致害的过程特征及其控制因素。结果发现,发生骤旱时土壤含水量下降呈先快后慢的变化趋势,叶片水分和叶水势则呈先慢后快的指数变化趋势。叶片光合生理指标对土壤水分的下降存在明显的阈值响应,且不同生理指标的阈值并不完全相同,其中净光合速率与表征叶片光合能力的指标（最大羧化速率）对土壤有效含水量的响应阈值为0.4,气孔导度和蒸腾速率对土壤有效含水量的响应阈值分别为0.5和0.4。而小麦光合生理指标对叶片水分和叶水势的阈值响应并不明显。同时依据各生理指标相关和通径分析结果得出,骤旱发生时引起小麦叶片净光合速率快速降低的主导因子为非气孔因素,而并不是以往作物受旱研究中的气孔因素。本研究结果有望丰富干旱影响认知,并可为科学应对干旱提供依据。     

杨柴对高CO2浓度和土壤干旱胁迫的响应

毛乌素优势植物杨柴 (HedysarummongolicumTurcz.)对高CO2 浓度和土壤干旱胁迫响应的研究结果表明 :干旱胁迫可使杨柴根系伸长 ,根生物量、地径、主茎高和茎生物量下降 ;高CO2 浓度使杨柴根和茎生物量明显增加 ,CO2 的“施肥效应”显著 ,干旱使CO2 的“施肥效应”减弱。同时 ,土壤干旱胁迫使杨柴的根 /冠比增加 ,说明在土壤干旱胁迫情况下根的生长比地上部分 (茎 )的生长更活跃 ,有利于提高杨柴在干旱沙漠地区的固沙作用 ;CO2 浓度升高和土壤干旱胁迫均使杨柴叶片的水势下降 ,叶片水势的下降使叶片细胞对水分的束缚力增强 ,从而减少植物蒸腾耗水 ,有利于提高水资源的利用效率     

华荠苧响应不同土壤水分的表型可塑性

研究了土壤相对含水量分别为100%、80%、60%、40%和30%水分条件下华荠FDB2(Mosla chinensis)生长和形态的表型可塑性.结果表明成年植株的生物量积累、形态参数、单株叶绿素总含量及穗重等都在60%相对含水量条件下最高;当土壤相对含水量从30%提高到60%时,分配到枝和根的生物量随之增加,分配到叶的生物量减少,土壤相对含水量再提高时,情况则相反;生殖比率随土壤相对含水量的下降而升高,30%处理最大,100%处理最小.这些结果说明华荠FDB2的适宜水分生态位是中偏湿的土壤环境.华荠FDB2通过器官生物量分配和形态结构调整对不同土壤水分产生可塑性响应,并以提高生殖比率的策略来适应干旱胁迫.     

土壤自然干旱处理对钩藤生长与生理特征及主要药用成分积累的影响

以一年生钩藤实生苗为试材,通过连续土壤控水12 d盆栽试验,研究持续性土壤自然干旱对钩藤幼苗生长、抗逆生理指标及其主要药用成分含量的影响。结果表明:(1)随着干旱胁迫时间的延长,钩藤根和茎叶生物量以及叶片相对含水量(RWC)显著持续下降(P0.05),而根冠比、叶片丙二醛(MDA)含量及相对电导率(REC)逐渐升高。(2)随着干旱胁迫时间的延长,钩藤叶片叶绿素a、b含量先增高后下降,叶片超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性先上升后下降,且POD活性最先达到峰值,CAT活性增幅最大;叶片中脯氨酸(Pro)、可溶性糖(SS)和可溶性蛋白(SP)含量逐渐升高,且Pro表现出更强的渗透调节能力。(3)钩藤幼苗叶片、主茎和带钩茎枝中钩藤碱与异钩藤碱含量随着干旱胁迫时间的延长而呈先增高后下降的趋势,响应时间先后顺序依次为叶片、主茎、带钩茎枝,生物碱含量由高到低依次为带钩茎枝、叶片、主茎。研究发现,在土壤持续自然干旱条件下,钩藤幼苗生长受到一定影响,但植株能通过提高其抗氧化酶活性和积累渗透调节物质来提高吸水和保水能力,有效抵御干旱逆境;且土壤自然干旱胁迫4～8 d有利于主要药效成分钩藤碱与异钩藤碱的积累;土壤相对含水量在42%～53%时,钩藤幼苗耐旱性较强且钩藤碱与异钩藤碱含量较高。     

白刺花幼苗对不同强度干旱胁迫的形态与生理响应

为了探讨白刺花 (Sophora davidii (Franch.) Skeels) 幼苗对持续干旱胁迫的适应能力及对策,用盆栽方法人工模拟土壤干旱条件,设置土壤田间持水量 (WHC) 100%、80%、60%、40%和20% 5个干旱胁迫处理,研究了幼苗生长、生物量分配、水分利用效率 (WUE) 、叶形态解剖结构以及光合色素等在不同干旱胁迫强度下的变化特点.结果显示,胁迫处理96d后,100% WHC条件下白刺花幼苗的总叶面积、分枝数、基径及最大根长等均最大;80% WHC对幼苗产生了轻度胁迫,随着干旱胁迫强度的进一步增加,幼苗生长显著减小.干旱胁迫限制了新生叶发生与单叶面积扩展,导致冠层总叶面积减小,从而引起幼苗光合能力及生物量积累均降低.随着胁迫强度的增加,叶生物量所占的比例及叶面积/根生物量的比值都明显减小,而根生物量所占的比例增大,这说明叶生长对干旱胁迫反应比根更加敏感.另外,干旱胁迫下WUE随着生物量与耗水量的减小而降低,表明幼苗具有浪费型水分利用对策.叶绿素 (Chla、Chlb和Chla+b) 及类胡萝卜素含量 (Car) 都随着干旱胁迫增强而呈增大趋势,但Chla/b及 Chl/Ca变化趋势相反.干旱胁迫对叶片解剖结构影响较小,土壤水分减少时仅栅栏组织厚度略有增厚,海绵组织变薄.研究结果证明,60% WHC是幼苗生长、生物量积累、WUE和光捕获复合体活性受到明显抑制的干旱胁迫强度阈值;20% WHC胁迫处理对幼苗产生了严重危害.但是在实验过程中,即使在20%WHC条件下也未出现叶片凋落及幼苗死亡,表明当年生白刺花具有较强的干旱忍受能力,幼苗通过减小地上蒸发面积、增加地下生长及叶绿素含量等多种形态与生理策略适应干旱胁迫.     

华荠Ning响应不同土壤水分的表型可塑性

研究了土壤相对含水量分别为100％、80％、60％、40％和30％水分条件下华荠Ning（Mosla chinensis）生长和形态的表型可塑性。结果表明：成年植株的生物量积累、形态参数、单株叶绿素总含量及穗重等都在60％相对含水量条件下最高;当土壤相对含水量从30％提高到60％时,分配到枝和根的生物量随之增加,分配到叶的生物量减少,土壤相对含水量再提高时,情况则相反;生殖比率随土壤相对含水量的下降而升高,30％处理最大,100％处理最小。这些结果说明华荠Ning的适宜水分生态位是偏湿的土壤环境。华荠Ning通过器官生物量分配和形态结构调整对不同土壤水分产生可塑性响应,并以提高生殖比率的策略来适应干旱胁迫。     

夏玉米叶片气体交换参数对干旱过程的响应

目前已经开展了大量的干旱对作物叶片气体交换参数影响的研究,但关于作物叶片气体交换参数对干旱过程的响应及其关键阈值的研究仍较少。基于夏玉米七叶期开始的5个初始水分梯度的长时间持续干旱模拟实验资料,分析了不同强度持续干旱过程中夏玉米叶片气体交换参数(净光合速率Pn,气孔导度Gs,蒸腾速率Tr,胞间CO_2浓度Ci和气孔限制值Ls)的变化规律及其关键阈值。结果表明,玉米的净光合速率(Pn),蒸腾速率(Tr)和气孔导度(Gs)在干旱发生初期呈大幅度下降,但随着干旱持续会出现一定的适应性。利用统计容忍限方法确定了夏玉米拔节期Pn,Tr和Gs响应干旱的临界土壤相对湿度(0—30cm)分别为53%,51%和48%,对应的临界叶含水率分别为81.8%,81.3%和81.2%。夏玉米光合作用由气孔限制向非气孔限制转换的0—30cm土壤相对湿度均为44%±2%,对应的叶含水率均为77.6%±0.3%。研究结果可为夏玉米干旱发生发展过程的监测预警提供依据。     

夏玉米叶片水分变化与光合作用和土壤水分的关系

叶片是光合作用的重要器官,其含水量的变化必将影响光合作用,但关于叶片水分变化对光合作用的影响报道较少。以华北夏玉米为研究对象,利用三叶期不同水分梯度的持续干旱模拟试验资料,分析夏玉米叶片水分变化及其与叶片净光合速率和土壤水分的关系。结果表明:夏玉米叶片净光合速率对叶片水分变化的响应显著且呈二次曲线关系,叶片含水量约为70.30%时,叶片净光合速率为零;叶片含水量与土壤相对湿度呈非直角双曲线关系,叶片最大含水量约为85.14%。研究结果可为准确描述叶片水分变化对光合作用的影响及客观辨识夏玉米干旱的发生发展及监测预警提供参考。     

夏玉米三叶期持续干旱下不同叶位叶片含水量变化及其与光合作用的关系

植物干物质的累积依赖于群体光合速率,而群体光合速率又与单叶的光合能力密切有关。叶片光合作用与其含水量密切相关,目前关于不同叶位叶片含水量对持续干旱的响应及其与光合作用的关系还未见报道。以华北夏玉米郑单958为材料,设置6个不同灌水处理,模拟不同灌溉量下持续干旱对夏玉米不同叶位叶片生理特性的影响,分析夏玉米顶部开始的第一、三、五叶位叶片的水分变化及其与净光合速率的关系。结果表明:夏玉米不同叶位的叶片最大含水量不同,且随干旱进程的推进叶片含水量的变化速率也不同,第一叶的叶片含水量下降速率高于第三、第五叶,第一叶的最大含水量高于第三、五叶,且可进行光合产物积累的叶片含水量下限随叶位的增加而增大。同时,第一叶的叶片含水量与土壤水分呈显著相关,且与净光合速率的相关性也非常强。第一叶可进行光合产物积累的叶片水分下限(净光合速率为零时的叶片含水量)最小,表明其耐旱性最强,对干旱具有指导意义。研究结果可为提高冠层光合作用模拟的准确性及夏玉米干旱发生发展的监测预警提供参考。     

干旱对夏玉米苗期叶片权衡生长的影响

叶片是植物对干旱响应最敏感的器官之一,叶片性状变化及其权衡关系能够反映植物对资源的利用策略以及对干旱的适应对策。基于2014年6个初始土壤水分梯度的夏玉米持续干旱模拟试验研究表明,随着干旱的发展,夏玉米各叶片性状均会受到影响,但不同干旱程度的影响不一致。基于水分胁迫系数及干旱持续时间提出了干旱程度的定量表达,随着干旱的发生发展,干旱程度在0—1之间变化。当干旱程度小于0.21时,夏玉米叶片性状不会受到显著影响;0.21—0.76时,叶片性状大小受到影响,但变化趋势不会发生改变;0.76—0.91时,新叶形成补偿不了老叶脱落,有效叶片数、叶干重、绿叶面积和叶含水量等性状提前出现下降趋势;大于0.91时,叶片生长几乎停滞。夏玉米叶片性状在干旱条件下的适应性生长本质上体现了其在快速生长与维持生存之间的权衡,但不同干旱程度下,夏玉米叶片性状生长的权衡策略不同:未发生干旱时,夏玉米倾向于维持较高的代谢活性,一旦干旱程度大于0,夏玉米就会降低叶片代谢活性;当干旱程度小于0.48时,夏玉米倾向于通过迅速增加叶面积来吸收较多的能量,以获得较大的生长速率,为生殖器官的生长及产量形成储备能量;当干旱程度大于0.48时,夏玉米会减小单叶面积以减少水分散失,倾向于资源贮存以提高其生存能力。     

Effect of plant growth promoting <Emphasis Type="Italic">Pseudomonas</Emphasis> spp. on compatible solutes,antioxidant status and plant growth of maize under drought stress

Drought is one of the major abiotic stresses affecting yield of dryland crops. Rhizobacterial populations of stressed soils are adapted and tolerant to stress and can be screened for isolation of efficient stress adaptive/tolerant, plant growth promoting rhizobacterial (PGPR) strains that can be used as inoculants for crops grown in stressed ecosystems. The effect of inoculation of five drought tolerant plant growth promoting Pseudomonas spp. strains namely P. entomophila strain BV-P13, P. stutzeri strain GRFHAP-P14, P. putida strain GAP-P45, P. syringae strain GRFHYTP52, and P. monteilli strain WAPP53 on growth, osmoregulation and antioxidant status of maize seedlings under drought stress conditions was investigated. Drought stress induced by withholding irrigation had drastic effects on growth of maize seedlings. However seed bacterization of maize with Pseudomonas spp. strains improved plant biomass, relative water content, leaf water potential, root adhering soil/root tissue ratio, aggregate stability and mean weight diameter and decreased leaf water loss. The inoculated plants showed higher levels of proline, sugars, free amino acids under drought stress. However protein and starch content was reduced under drought stress conditions. Inoculation decreased electrolyte leakage compared to uninoculated seedlings under drought stress. As compared to uninoculated seedlings, inoculated seedlings showed significantly lower activities of antioxidant enzymes, ascorbate peroxidase (APX), catalase (CAT), glutathione peroxidase (GPX) under drought stress, indicating that inoculated seedlings felt less stress as compared to uninoculated seedlings. The strain GAP-P45 was found to be the best in terms of influencing growth and biochemical and physiological status of the seedlings under drought stress. The study reports the potential of rhizobacteria in alleviating drought stress effects in maize.     

CAM variations in the leaf-succulent Delosperma tradescantioides (Mesembryanthemaceae), native to southern Africa

Drought responses of diurnal gas exchange, malic acid accumulation and water status were examined in Delosperma tradescantioides , a succulent that grows in drought-prone microenvironments in summer rainfall and all-year rainfall regions of southern Africa. When well-watered, this species exhibited Crassulacean acid metabolism (CAM)-cycling, but its carbon fixation pattern changed during the development of drought, shifting to either low-level CAM or to CAM-idling. The rate and pattern of this change depended on environmental conditions, duration of water stress and leaf age. At the onset of drought, diurnal malate fluctuation increased, but was strongly depressed (by ca 70%) as drought continued, and when leaf water content and water potential were low (ca 35 and 50% of the initial levels, respectively). When rewatered, rates of growth and photosynthesis, gas exchange and water status recovered fully to pre-stressed values within two days. Whole-shoot carbon uptake rates suggested that leaf growth had continued unabated during a short-term (≅ one week) drought. This emphasises that CAM-idling allows the maintenance of active metabolism with negligible gas exchange when soil water is limiting. It is possible that old or senescent leaves may provide water for the expansion of developing leaves during initial periods of drought. Regardless of the water regime and environmental conditions, leaf nocturnal malate accumulation and water content were positively correlated and increased with leaf age. Thus the gradual loss of water from older mature leaves may induce CAM-idling, which reduces water loss. An important ecological consequence of this combination of CAM modes is the potential to switch rapidly between fast growth via C₃ gas exchanges when well-watered to water-conserving CAM-idling during drought.     

CAM variations in the leaf-succulent Delosperma tradescantioides (Mesembryanthemaceae), native to southern Africa

Drought responses of diurnal gas exchange, malic acid accumulation and water status were examined in Delosperma tradescantioides , a succulent that grows in drought-prone microenvironments in summer rainfall and all-year rainfall regions of southern Africa. When well-watered, this species exhibited Crassulacean acid metabolism (CAM)-cycling, but its carbon fixation pattern changed during the development of drought, shifting to either low-level CAM or to CAM-idling. The rate and pattern of this change depended on environmental conditions, duration of water stress and leaf age. At the onset of drought, diurnal malate fluctuation increased, but was strongly depressed (by ca 70%) as drought continued, and when leaf water content and water potential were low (ca 35 and 50% of the initial levels, respectively). When rewatered, rates of growth and photosynthesis, gas exchange and water status recovered fully to pre-stressed values within two days. Whole-shoot carbon uptake rates suggested that leaf growth had continued unabated during a short-term (∼ one week) drought. This emphasises that CAM-idling allows the maintenance of active metabolism with negligible gas exchange when soil water is limiting. It is possible that old or senescent leaves may provide water for the expansion of developing leaves during initial periods of drought. Regardless of the water regime and environmental conditions, leaf nocturnal malate accumulation and water content were positively correlated and increased with leaf age. Thus the gradual loss of water from older mature leaves may induce CAM-idling, which reduces water loss. An important ecological consequence of this combination of CAM modes is the potential to switch rapidly between fast growth via C₃ gas exchanges when well-watered to water-conserving CAM-idling during drought.     

Gas exchange and leaf metabolism of irrigated maize at different growth stages

Abstract

Net ecosystem exchange (NEE), leaf gas exchange and biochemical traits were investigated in an irrigated maize crop grown under Mediterranean conditions. Sub-optimal irrigation water supply determined a drought stress during the early vegetative growth stage (45–49 days after swing) that decreased NEE. Drought, in the late vegetative stage, also caused a reduction of leaf gas exchange. In the latter period, proline, glycine and serine, as well as sucrose leaf contents increased, while starch, proteins and glucose contents decreased. In the early reproductive stage, the crop experienced a longer dry spell that induced a reduction in canopy as well as in leaf gas exchanges, while protein and free amino acid contents decreased with respect to the late vegetative stage. Both ecophysiological and biochemical data demonstrate a good capacity of cultivar Pioneer PR32D99 to endure the environmental stress, related to Mediterranean summer drought, leading to an elevated dry matter yield at harvest. Photosynthetic apparatus appeared fairly resistant to soil water shortage due likely to the increased leaf content of organic solutes, such as amino acids and soluble sugars.     

The effect of CaCl<Subscript>2</Subscript> on calcium content,photosynthesis, and chlorophyll fluorescence of tung tree seedlings under drought conditions

The study investigated the effects of different CaCl₂ concentrations (2, 5, and 10 mM) on photosynthetic enzymatic activities, photosynthesis, and chlorophyll fluorescence of tung tree seedlings under drought conditions. Plants were sprayed with either CaCl₂ or distilled water until run-off. Irrigation was then withheld to induce drought stress. The strength of drought stress was evaluated by relative leaf water content and soil water content, which was 27.3 and 9.5% on day 0 and day 12, respectively. Drought stress decreased activities of ribulose-1,5-bisphosphate carboxylase/oxygenase and phosphoenolpyruvate carboxylase, chlorophyll (a+b) content, net photosynthetic rate, stomatal conductance, transpiration rate, electron transport rate, the maximal quantum yield of PSII photochemistry, and effective quantum yield of PSII in tung tree seedlings. The CaCl₂ pretreatments alleviated the negative effect of drought stress to some degree on all the parameters mentioned above.     

干旱胁迫下杨树无性系苗期光合与气孔形态变异研究

为了解不同干旱胁迫处理下,杨树叶片光合特性和气孔形态的变化规律,本研究以4个杨树无性系为材料,对其干旱胁迫下光合指标与气孔形态指标进行测定分析,方差分析结果表明：除气孔器长在处理间差异不显著外,其他性状在无性系间、处理间和无性系与处理交互作用间均达极显著差异水平。随着土壤相对含水量的逐渐降低,无性系净光合速率、蒸腾速率和气孔导度都呈现出不同程度的下降;而胞间二氧化碳浓度呈现为先降后升趋势,表明当土壤相对含水量大于40%时,光合作用的主要限制因子是气孔因素,当土壤相对含水量低于40%时,光合作用的主要限制因子转换为非气孔因素。气孔形态研究结果表明,各指标均随土壤相对含水量的持续降低呈现出持续下降趋势。利用隶属函数法对不同干旱胁迫下4个杨树无性系的抗旱性进行综合评价,结果表明：白城小青黑杨的抗旱性优于其他三个无性系。