黑杨无性系间长期水分利用效率差异的生理基础

试验于2003年6月10日至8月20日在温室中进行,采用完全随机区组设计,4个水分处理（充分供水、轻度胁迫、中度胁迫、重度胁迫）,6次重复.各水分处理严格控制浇水间隔：充分供水,每2d浇水1次;轻度胁迫,每3d浇水1次;中度胁迫,每4d浇水1次;重度胁迫,每5d浇水1次.每次浇水的量相同,500ml.试验材料为美洲黑杨杂交无性系,父本为哈佛杨（Populus deltoides Bartr.CI.‘Harvard＇）,母本为山海关杨（Populus deltoides Bartr.CV.‘shanhaiguanensis＇）,共10个无性系,编号为J1～J10.以当前优良品系108杨（Populus euramericana CV.‘114/69＇）和中林46杨（Populus deltoides Bartr.CV.‘Zhonglin 46＇）为对照,编号为CK1、CK2.测定了12个无性系间长期水分利用效率（WUEL）、光合参数（净光合速率Pn、蒸腾速率Tr、气孔导度Gs、瞬时水分利用效率WUEi、最大净光合速率Pmax、光饱和点LSP、羧化效率Ce）及气孔特征参数（气孔频度、气孔大小、上/下表皮气孔数目比）、根冠比的差异,并深入分析了光合参数与WUEL、气孔特征参数与WUEL、根冠比与WUEL及光合参数之间的相互关系.结果表明：无性系间WUEL存在差异,这种差异随水分胁迫的加剧而更加显著.无性系间WUEL的差异在4个水分处理下表现出一致性,即WUEL最优的都是J2,其次为J6、J7、J8、J9.高WUEL的J2等无性系其气孔频度、气孔大小、Gs、Tr、Pn和根冠比在所有无性系中都处于适中的位置.它们的上/下表皮气孔数目比大,Pmax、LSP、Ce明显优于对照.Pmax高、LSP高、Ce大,表明高WUEL的J2等无性系光合能力强.Gs、Tr、Pn适中,表明J2等无性系在保证具有高WUEi的同时能保持较强的光合能力.根冠比适中,表明J2等无性系的光合产物在根、冠之间分配合理,能有充足的根系分布保证水分的供应,同时又有较多的光合产物积累在地上部分.气孔特征参数的差异是导致无性系间光合能力和WUEi差异,并最终导致WUEL差异的一个主要因子.气孔频度和气孔大小适中的无性系,其Gs、Tr、Pn适中,WUEi较高;上/下表皮气孔数目比大的无性系则具有较强的光合能力.无性系间WUEL的差异是一系列具有差异的生理参数共同作用的结果,高WUEL的无性系通常光合能力强、WUEi高、根冠比适中.今后工作中选育高WUE的无性系时,除需关注单个生理参数的突出作用外,更应关注生理参数的协同作用.     

枫杨幼苗对土壤水分"湿-干"交替变化光合及叶绿素荧光的响应

以盆栽1年生枫杨幼苗为实验材料,通过人工设置土壤水分来模拟三峡库区消落带不同土壤水分对枫杨幼苗的光合参数、光合色素含量、叶绿素荧光特性等的影响.试验设置4个处理组,分别为常规供水、常规供水-轻度干旱-复水、水淹、水淹-轻度干旱-复水,3个处理期分别为前期(0-33 d)、中期(34-63 d)、后期(64-78 d).结果表明,不同的水分处理显著地影响了枫杨幼苗“表观性”的气体交换、光合色素含量和水分利用效率等特性,但相较而言对枫杨幼苗“内在性”的叶绿素荧光特性影响较小,且影响的结果和程度因处理组和指标而异.78 d时,除胞间CO2浓度(Gi)、叶绿素a/叶绿素b、光化学猝灭值(qP)和非光化学淬灭值(qN)外,水淹组(FL组)的各项指标在4个处理组中都为最低值;“湿-干”交替组(FD组)的净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)及总叶绿素含量则表现出先降低复水后显著增加的趋势;DR组的变化趋势与FD组类似,但变化的幅度较FD组小.研究发现,枫杨幼苗面对不同水分状况呈现出了一定的敏感特性,但随着胁迫时间的延长其无论是从光合、水分利用还是叶绿素荧光特性方面都表现出积极的响应,较能适应干旱、水淹、“湿-干”交替等多种环境胁迫,且在胁迫解除后能够迅速恢复生长,可以考虑用于三峡库区消落带的植被重建.     

正常和环割条件下不同形态氮素添加对红椎幼苗光合特性的影响

采用盆栽试验和韧皮部环割方法研究了碳水化合物供应、氮素形态及其交互作用对红椎幼苗叶片光合特性的影响。无机氮源采用硝酸铵(AN)、铵态氮(NH_4~+-N)、硝态氮(NO_3~--N),有机氮源采用尿素(Urea)、精氨酸(Arg)和甘氨酸(Gly),氮素施用量均为10g N/m~2,处理时间为10 d。研究结果表明,环割、氮素形态及其交互作用均显著影响了红椎幼苗叶片的净光合速率(Pn);单一环割处理显著降低了红椎幼苗叶片Pn、气孔导度(Gs)、胞间CO_2浓度(Ci)、蒸腾速率(Tr)、相对叶绿素含量和CO2利用效率(CUE),但显著提高了叶片水分利用效率(WUE)和气孔限制值(Ls),其叶片Pn降低主要是由气孔限制和叶绿素含量降低所导致的。正常条件下,所有氮素形态处理均显著降低了红椎幼苗叶片的Pn、Gs、Ci和Tr,但显著升高了叶片Ls和WUE,其叶片Pn降低的主要原因是供氮过高引起的叶片气孔限制。正常条件下,除Arg处理外,其他氮素形态均显著升高了红椎幼苗叶片的CUE,其中以Gly处理的促进作用最大。环割条件下,3种有机态氮素的添加均显著缓解了单一环割处理对红椎幼苗叶片Pn的抑制作用,尤其以精氨酸最为明显,供应精氨酸的叶片Pn值从单一环割处理的强烈抑制中恢复到了对照水平,而无机态氮的供应均未显著改变这种抑制。结果表明短期碳水化合物供应的阻断会显著抑制红椎幼苗叶片的光合能力,适量供应精氨酸、甘氨酸和尿素等有机态氮会有效缓解这种抑制作用,其中以精氨酸的作用最为明显。     

镉胁迫下硒对罗汉果组培苗光合特性的影响

实验以罗汉果组培苗为材料,室内栽培在内装市售营养土的塑料盆中,以0、10、50、100、200mg·kg-1浓度镉离子和1mg·kg-1浓度硒处理,培养20d后分析罗汉果幼苗的相关光合生理指标。结果表明:低浓度Cd2+对叶片叶绿素含量、光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)影响不大或稍有上升,但高浓度镉离子处理植株叶片的叶绿素含量、光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)明显下降;随Cd2+处理浓度的增加,叶片胞间CO2浓度(Ci)呈现上升趋势;加硒则延缓叶绿素下降,促进光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)上升,降低叶片胞间CO2浓度(Ci)。表明高浓度镉离子的毒害导致罗汉果组培苗叶片光合性能受到伤害,从而影响罗汉果幼苗生长。镉硒混合处理反映出硒对镉的毒害有缓解作用。     

海岸不同坡向滨麦光合特性与风速异质环境的关系

在自然条件下,测定分析了夏季和秋季静风天及秋季大风天,海岸沙丘不同坡向环境因子及滨麦株高、叶片叶绿素含量、土壤含水量和光合日变化特性,以期明晰滨麦响应不同风速环境的生理调控机理。结果表明,不同坡向环境异质性明显,滨麦形态可塑性强。海岸迎风坡风大、温度低、湿度大,滨麦植株低矮、叶绿素含量较高;背风坡温度高、土壤干旱、空气流动差,滨麦植株高大,叶绿素含量低。在夏秋季静风天,迎风坡和背风坡滨麦叶片Pn出现光合"午休"现象,但迎风坡滨麦日均Gs、Tr、Pn均显著高于背风坡;而在秋季大风天,迎风坡和背风坡滨麦叶片Pn"午休"现象消失,并且背风坡滨麦日均Pn、Tr、Gs均显著高于迎风坡滨麦。同坡向相比,秋季大风天迎风坡滨麦日均Pn、Tr、Gs明显较秋季静风天低,而背风坡滨麦日均叶片Pn、Tr、Gs却较静风天分别增高126%、66.3%、134%。强海风吹袭引发迎风坡温度降低、滨麦叶片摇摆、气孔导度降低导致Pn下降,而强海风使背风坡空气流动加快、温度降低、气孔导度增大、"午休"消失使Pn增高。不同坡向滨麦对不同海风风速的适应表现出明显的光合生理可塑性,它在滨麦适应不同风力、提高其光合速率和增加物质积累上具有重要作用。而滨麦的形态和光合生理可塑性可能是其在不同海风强度下生存、生长、实现种群扩张的重要生理调控机理,这一特性在未来作物、牧草和树木抗风、抗盐育种中具有重要应用价值。     

山黧豆幼苗对干旱胁迫的生理响应

用PEG6000模拟干旱对山黧豆进行胁迫。结果发现,胁迫初期（0~48 h）,突然的水分亏缺使气孔导度（Sc）和蒸腾速率（Tr）迅速下降,而净光合速率（Pn）和水分有效利用率（WUE）基本维持稳定。胁迫后期（48~108 h）,上述四个光合指标均不同程度地向对照水平恢复;脯氨酸和相对电导率（REC）受胁迫强度影响较小,但与胁迫时间呈明显正相关,分别在48和60 h增幅最大,而且当REC上升至对照的50%左右时,脯氨酸含量已达对照的14倍之多。由此认为,山黧豆可能主要通过迅速减小Sc和Tr以及大量而急剧的积累脯氨酸来减轻干旱所造成的伤害。     

控水与补水条件下连续热浪对闽楠光合特性和生长速率的影响

全球变暖背景下,亚热带地区极端气候热浪事件发生频率持续增加。高频热浪及其伴随的高温和干旱复合胁迫将严重影响植物的光合特性,抑制植物的生长,甚至造成死亡。然而,目前亚热带树木光合特性及生长对高频热浪及复合胁迫的响应仍不明确。以亚热带阔叶树种闽楠苗木为研究对象进行了热浪模拟实验,关注了补水和控水处理不同水分环境下连续热浪对闽楠光合特性及生长速率的影响。结果表明,补水处理下闽楠净光合速率(Pn)在单次热浪影响下显著下降了34%,同时水分利用效率显著(WUE)下降,但蒸腾速率(Tr)、气孔导度(Gs)和叶片水汽压亏缺(Leaf_vpd)显著上升(P<0.05)。表明水分充沛的高温环境中闽楠可通过增加蒸腾耗水加速水分蒸散来调节叶片的温度,增强植株光合特性对热浪的抗性。而控水处理下单次热浪处理组Tr和Gs未显著上升,以及Tr与Leaf_vpd在干湿环境下线性拟合的不同斜率,说明水分胁迫会降低叶片降温的效率,加剧热浪对闽楠光合特性的影响。水分和高温的复合胁迫还延长了闽楠光合特性在热浪后的恢复过程,高温胁迫下闽楠Pn在15 d后恢复至未干扰水平,但复合胁迫...     

不同水分处理下喀斯特土层厚度异质性对两种草本叶片解剖结构和光合特性的影响

为了探究不同水分处理下草本植物对喀斯特土层厚度变化的叶片形态建成和光合生理响应,以黑麦草(Lolium perenne L.)和苇状羊茅(Festuca arundinacea Schreb.)为研究对象,通过盆栽水分受控试验,研究了3种水分处理[正常供水(W_(ck)),减水1组(D1)和减水2组(D2)]下3种土层厚度[浅土组(S_S)、对照组(S_(CK))和深土组(S_D)]对两种草本叶片解剖结构和光合特性的影响。结果表明:(1)正常供水下(W_(ck)),黑麦草和苇状羊茅在浅土组(S_S)的气孔密度和气孔限制值(Ls)均显著高于对照组(S_(CK)),净光合速率(Pn)、胞间CO_2浓度(Ci)和蒸腾速率(Tr)降低;在深土组(S_D),两种植物的气孔密度都有所下降,黑麦草的叶脉密度、Pn和Tr均低于对照组,而苇状羊茅的叶脉密度和Pn表现出增加;(2)D1水分条件下,黑麦草在浅土组的气孔密度较对照组增加,叶脉密度、Pn和Tr均降低,而苇状羊茅的气孔密度有所降低,叶脉密度、Pn和Tr未受到显著影响;在深土组中,黑麦草的气孔密度不变,叶脉密度增加,而Pn和Tr均降低;苇状羊茅的气孔密度降低,但叶脉密度、Pn和Tr均升高;(3)D2水分条件下,两种植物在浅土组的叶脉密度较对照组均增加,气孔密度、Pn和Tr均受到抑制;在深土组,黑麦草的远轴面气孔密度较对照组下降,两种植物的其他指标未受到明显影响。可见,在不同水分条件下,植物的叶片解剖结构和光合特性对不同土层厚度的响应不一,且不同物种间也有差异。总体上随着水分减少,土层厚度降低对植物的光合抑制作用增强,而厚度增加对深根植物的光合促进作用和对浅根植物的光合抑制作用先增强后减弱。植物气孔和叶脉性状特征随水分条件的变化在一定程度上与叶面积和叶片宽度的变化有关。     

秸秆隔层对盐碱土水盐运移及食葵光合特性的影响

在内蒙古河套灌区通过微区试验,研究了秸秆深埋(S)、上盖秸秆下埋秸秆(简称上秸下秸,S+S)、上盖地膜下埋秸秆(简称上膜下秸,P+S)和地膜覆盖(对照,CK)4种耕作措施对0-40 cm土层水盐运移及食葵光合特性的影响.结果表明:(1)不同措施对土壤水盐调控的效果与作用时期差异较大.P+S在整个生育期内土壤盐分含量和盐溶质浓度较低,控盐效果显著;S+S仅在苗期能保墒控盐,但控盐效果比P+S差,后期出现水减盐增现象,保墒控盐效果也不佳;S在整个生育期内土壤盐分含量和盐溶质浓度最高,控盐效果最差;CK在整个生育期内土壤水分含量变化不大,而盐分含量较高,控盐效果也不明显.(2)不同措施对土壤水盐运移调控程度的差异,导致食葵光合特性也有明显变化.与CK、S、S+S相比,P+S由于其较低的盐溶质浓度环境,明显改善了其光合特性,在苗期、蕾期和花期能提高净光合速率(Pn)和蒸腾速率(Tr),增加气孔导度(Gs),降低胞间CO2浓度(Ci),从而使其作物长势和干物质积累明显高于其它措施.综合试验结果,P+S是内蒙古河套灌区盐碱地改良中优选的控抑盐耕作措施.     

AM1 is a potential ABA substitute for drought tolerance as revealed by physiological and ultra-structural responses of oilseed rape

Abscisic acid (ABA) is an important signaling molecule for plants under drought tolerance. However, ABA itself has many limitations to be used in agriculture practically. Recently, AM1 (ABA-mimicking ligand) has been found to replace ABA. In this study, we have investigated AM1’s potential role for drought tolerance by growing two contrasting rapeseed (Brassica napus L.) genotypes: Qinyou 8 (drought sensitive) and Q2 (drought resistant) with exogenous ABA or AM1 application under well-watered and drought-stressed conditions. Results demonstrate that drought stress has hampered plant growth (relative height growth rate, plant biomass, leaf area), plant water status (leaf relative water content, root moisture content, leaf water potential), photosynthetic gas exchange attributes like net photosynthesis rate (Pn), stomatal conductance (Gs), intercellular CO₂ concentration (Ci), transpiration rate (E); chlorophyll fluorescence parameters like photosynthetic efficiency (Fv/Fm), effective quantum yield of PSII (Φ _PSII ), photochemical quenching coefficient (qL), electron transport rate (ETR) and chlorophyll content, especially for Qinyou 8 significantly compared to well-watered plants. Whereas increased root/shoot ratio (R/S), water use efficiency (WUE) and non-photochemical quenching (NPQ) was recorded in both genotypes under drought stress. On the other hand, exogenous ABA or AM1 treatment has regulated all the above parameters in a rational way to avoid drought stress. Chloroplast transmission electron microscope images, especially for Qinyou8, have revealed that oxidative stress induced by drought has blurred the grana thylakoids, increased the size or number of plastoglobules due to lipid peroxidation, and the presence of starch granules depict weak capacity to convert them into simple sugars for osmotic adjustment. However, intact grana thylakoid, few plastoglobules with no or very few starch granules were observed in the chloroplast from ABA- or AM1-treated plants under drought. More importantly, AM1-treated plants under drought stress have responded in an extremely similar way like ABA-treated ones. Finally, it is suggested that AM1 is a potential ABA substitute for plant drought tolerance.     

钙素对彩叶玉簪光合作用和保护酶活性的影响

该文以彩叶玉簪为材料,研究了不同钙素水平对玉簪叶片光合作用和保护酶活性的影响。结果表明:随着钙素水平的提高,彩叶玉簪叶片的净光合速率(Pn)、气孔导度(Gs)、胞间CO_2浓度(Ci)、蒸腾速率(Tr)和最大光化学效率(F_v/F_m)均呈单峰曲线,最高峰值出现在Ca~(2+)90 mg·L~(-1)时;电子传递速率(ETR)的变化也呈单峰曲线,峰值出现在Ca~(2+)50 mg·L~(-1)时;初始荧光(F_0)和最大荧光(F_m)值在0~360 mg·L~(-1)钙素水平下呈先升高后下降再升高的趋势,最大值均出现在90 mg·L~(-1)时;Pn和Gs值的变化与Ci值成正相关。同时叶片中过氧化物酶(POD)、过氧化氢酶(CAT)的活性及丙二醛(MDA)、可溶性蛋白质(SP)含量均表现为单谷曲线,在Ca~(2+)90 mg·L~(-1)时达最小值。超氧化物歧化酶(SOD)活性呈现持续下降趋势。综上所述,彩叶玉簪Pn下降主要由气孔引起,叶面喷施90 mg·L~(-1)的Ca~(2+)可增强彩叶玉簪光合作用,降低保护酶活性。     

Changes in leaf photosynthetic characteristics and water use efficiency along with tree height of 4 tree species

As main photosynthetic organs, leaves are very sensitive to exterior environments. Water deficiency obviously affects the biological and physiological characteristics of leaves. Xylem pathways increase when trees grow tall, which results in the increase in water gravity as well as pathway resistance. Accordingly, the physiological characteristics of leaves change along with tree height. In this research, the photosynthetic characteristics and carbon isotope ratio (δ¹³C) in the leaves of 4 tree species, Platanus hispanica, Robinia pseudoacacia, Fraxinus chinensis and Ginkgo biloba, were measured. The results showed that the leaf photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Cond) and internal CO₂ concentration (Ci) reduced along with tree height, while the leaf δ¹³C increased along with tree height. The One Way ANOVA and LSD tests showed that the leaf photosynthetic characteristics and δ¹³C varied significantly at different tree heights (P < 0.05). The decrease in leaf photosynthetic capability and the increase in δ¹³C along with tree height indicate that the leaves at the tree tops suffer from water stress. These results support the hydraulic limitation hypothesis.     

Responses of young ‘Pink lady’ apple to alternate deficit irrigation following long-term drought: growth, photosynthetic capacity, water-use efficiency, and sap flow

We studied photosynthetic capacity, growth, sap flow, and water-use efficiency in young trees of ‘Pink Lady’ apple (Malus domestica) that were exposed to 60 d of moisture stress. Three irrigation schemes were tested in the greenhouse: well-watered control; drought; or alternate deficit irrigation (ADI). Compared with the drought-stressed plants, those treated via ADI showed better height growth, larger scion diameters, and greater total leaf area, as well as significantly increased gains in dry biomass and rootstock diameters. However, their performance was still significantly lower than that demonstrated by continuously well-watered plants. Sap flow was greater under ADI than under drought, but less than under control conditions. The average rate of net photosynthesis, total amount of irrigation water applied, and dry biomass gain had highly significant and positive linear correlations with long-term water-use efficiency (WUE_L). The same was true between average stomatal conductance and WUE_L. By contrast, instantaneous water-use efficiency (WUE_I) was very significantly and negatively correlated with WUE_L. In addition, values for WUE_L were much higher from well-watered plants when compared with either drought-stressed trees or those treated per ADI. Therefore, our results indicate that, although ‘Pink Lady’ apple normally has high WUE, it still consumes a large amount of water. Therefore, the practice of ADI following a period of long-term drought could be used to improve growth and WUEL by this cultivar.     

Photosynthetic parameters and carbon reserves of a resurrection plant <Emphasis Type="Italic">Reaumuria soongorica</Emphasis> during dehydration and rehydration

The effects of dehydration and subsequent rehydration on photosynthetic parameters and carbon reserves were investigated in the resurrection plant Reaumuria soongorica. Dehydration was imposed by withholding water and covering plants with a PVC sheet when it rained, over a period of 53 days, by which time all leaves had been shed. Thereafter, plants were watered at 7-day intervals. The diurnal course of the net photosynthetic rate (Pn) was bimodal under well-watered conditions. After a period of withholding water, the second peak disappeared, and Pn, instantaneous water use efficiency (WUE), stomatal conductance (gs) and intercellular CO₂ concentration (Ci) decreased, but sugar, starch and non-structural carbohydrate (NSC) reserves increased. It was concluded that under the conditions of high temperature and dehydration, the reduction of Pn should be mainly attributed to gs. On rehydration Pn, gs, Ci and WUE increased slightly in the stem. Accompanying new leaf production, carbon reserves in the stem decreased. This indicated that carbon reserves in the stem have two important ecological roles, survival during dormant periods and support of vegetative regrowth following rehydration.     

干旱胁迫下广东石漠化地区造林树种光合和耗水特性

石漠化地区土层稀薄、干旱贫瘠、植被破坏、生态恶化等问题较为突出,人工恢复森林植被是一项快速有效的生态恢复途径。采用盆栽苗木称重法和Li-6400光合系统测定方法分别测定3个常见石漠化造林树种浙江润楠(Machilus leptophylla),枫香(Liquidambar formosana)和亮叶含笑(Michelia fulgens Dandy)苗木在不同土壤水分条件下耗水特性和光合特性,为进一步筛选和评价石漠化地区造林树种抗旱特性提供理论依据。研究结果表明:(1)整个干旱胁迫期间,3种幼苗叶片的净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)和胞间CO_2浓度(Ci)持续下降。重度干旱时,浙江润楠光合和水分利用效率分别是枫香的2.5倍、89.6倍和亮叶含笑的1.9倍、26.3倍。(2)干旱胁迫中期和后期,枫香和亮叶含笑净光合速率(Pn)和气孔导度(Gs)下降而胞间CO2浓度(Ci)升高,说明Pn下降的主要原因已经由气孔因素转变为非气孔因素的限制。(3)3个石漠化树种在不同干旱胁迫下日耗水总量和日平均耗水速率均存在显著性差异(P0.05),白天耗水量占总耗水量74%—92%之间。浙江润楠在重度干旱时期还对水分要求还比较大,维持一个相对较高的耗水速率,是枫香和亮叶含笑的3.7倍和2.2倍。(4)不同干旱胁迫下,3个石漠化树种耗水速率日变化均表现出单峰曲线,不同干旱胁迫下峰值点会发生变化。(5)综合来看,浙江润楠和枫香是相对高光合和高水分利用效率树种。隶属函数结果表明,在正常、轻度和重度干旱下抗旱能力均为枫香浙江润楠亮叶含笑,重度干旱下为浙江润楠枫香亮叶含笑。     

An integrated diagnostic approach to understand drought tolerance in mulberry (Morus indica L.)

Four popular mulberry cultivars (Morus indica L. cvs.V-1, MR-2, S-36 and K-2) were assessed for drought tolerance with an integration of selective approaches. The potted plants were subjected to two watering treatments for 75 days: control pots were watered up to 100% field capacity (FC) and stressed pots were maintained at 25–30% FC. Net photosynthetic rate (P_n), stomatal conductance (g_s), transpiration rate (E) and instantaneous water use efficiency (WUE_i) were the key parameters to assess photosynthetic gas exchange performance. Drought caused marked down-regulation in leaf gas exchange in all cultivars (cvs) except V-1 which maintained better P_n, g_s, E and higher WUE_i under severe water deficit. All the four cvs also showed differential antioxidative responses under water stress. Higher concentrations of carotenoids, ascorbic acid, glutathione, α-tocopherol and proline were observed in the leaf extracts of V-1, while minimum accumulation of those metabolites was recorded with K-2 and S-36. An endogenous loss of α-tocopherol and higher lipid peroxidation were encountered in K-2, S-36 and MR-2, whereas V-1 showed minimum lipid peroxidation under water deficit regimes. Comparative morpho-anatomical analysis revealed a well-developed root system and a better anatomical architecture in V-1 which could further contribute tolerance during drought stress.     

Photosynthetic characteristics and water use efficiency of three coastal dune plants

To clarify the ecophysiological characteristics of plants growing on a coastal dune, net photosynthetic rate (Pn) and leaf conductance (g1) of three perennial species in Japanese coastal regions,Ischaemum anthephoroides (C₄),Carex kobomugi (C₃) andCalystegia soldanella (C₃), were compared under controlled environmental conditions and field conditions at the kado-ori coast at Ohno Village, Ibaraki.I. anthephoroides achieved photosynthetic CO₂ saturation at ca. 100 μll⁻¹ intercellular CO₂ concentration (C ₁), and itsPn was not light-saturated at a high photosynthetically active photon flux density (PPFD) of 1000 μmol m⁻²s⁻¹. This C₄ species showed a high optimal leaf temperature forPn (35°C) and a lowg1 (0.1 mol H₂O m⁻²s⁻¹), permitting maintenance of the highest water use efficiency (WUE, the ratio ofPn to transpiration rate (Tr)) in the field among the three species. At light saturation,C. soldanella had the lowestPn andg1 and a similar carboxylation efficiency related toC ₁ (Pn/C₁ ratio) asCarex kobomugi. Calystegia soldanella also had a high optimal temperature forPn (30°C), and achieved higherWUE thanCarex kobomugi, as a result of efficient stomatal regulation. In contrast, at the optimum temperatureC. kobomugi had a highPn comparable toI. anthephoroides due to a highg1 of 0.3 mol H₂O m⁻²s⁻¹, but with high temperature treatmentsPn andg1 were significantly decreased.C. kobomugi always had the lowestWUE among the three species in the field. It is therefore clear thatI. anthephoroides is a heat-resistant species,Calystegia soldanella is a heat-enduring species andCarex kobomugi is a heat-evading species due to its eraly phenology.     

Responses of Nitraria tangutorum to water and photosynthetic physiology in rain enrichment scenario

Under the global warming conditions, great attention has been paid to the effects of precipitation on ecophysiological characteristics in desert plants. Nitraria tangutorum is one of the dominant shrubs distributes in desert outside Minqin oasis, Gansu Province. The artificial simulated rainfall experiments were carried out in four consecutive years from 2008 to 2011, in an attempt to understand the mechanisms of the photosynthetic response in desert plant to the variation of future precipitation pattern. The water and photosynthetic physiological characteristics of leaves in N. tangutorum were examined from July 24 to 26 in 2011 under different simulated rainfall increase gradients (increased 0%, 25%, 50%, 75% and 100% of mean annual precipitation, respectively). We measured leaf traits that could reflect both leaf water status (e.g., leaf water content and leaf water potential) and photosynthetic physiology (e.g., maximum net photosynthetic rate). The results showed that leaf water content and leaf water potential of N. tangutorum increased with increasing rainfall. Leaf water content and leaf water potential of N. tangutorum in the 100% increased rainfall treatment were significantly greater by 8.51% and 12.07% than the control (0% increased rainfall treatment). But leaf dry matter content and specific leaf weight gradually decreased with increasing rainfall. Leaf dry matter content and specific leaf weight in the 100% increased rainfall treatment were significantly lower by 6.92% and 25.93% than the control. Leaf maximum net photosynthetic rate (A_max), apparent quantum yield (AQY) and light saturation point (LSP) increased with increasing rainfall, while light compensation point (LCP) gradually decreased with increasing rainfall. AQY in the 100% increased rainfall treatment was significantly greater by 70.00% than the control. However, there were no significant differences in LSP and LCP between different treatments. A_max, transpiration rate (T_r), stomatal conductance (G_s) in the 100% increased rainfall treatment were significantly greater by 81.91%, 166.07% and 110.47% than the control, respectively. On the contrary, water use efficiency (WUE) in the 100% increased rainfall treatment was significantly less 48.28% than the control. There were no significant differences in intercellular CO₂ concentration (C_i) and stomatal limitation value (L_s) between different treatments. The correlation analysis showed that there were significantly positive correlations between leaf water content, leaf water potential, T_r and G_s. However, there were significantly negative correlations between leaf dry matter content, leaf specific mass and T_r, G_s, leaf water content and leaf water potential, suggesting that leaf gas exchanges were regulated by leaf water status. Therefore, N. tangutorum could adapt to the tendency of future increasing precipitation by the coordination of water physiology and photosynthesis.     

Growth, gas exchange, and water-use efficiency response of two young apple cultivars to drought stress in two scion-one rootstock grafting system

The combination of two scion-one rootstock was used for two apple cultivars, ‘Pink Lady’ and ‘Qinguan’, budded on the same, one-year-old Malus hupehensis (Pamp.) Rehd. to reduce the impact of root and pot size and in order to understand the growth, water-use efficiency (WUE), and chlorophyll fluorescence characteristics. The two-scion grafted trees were planted in plastic pots under two water regimes, i.e. 70% field capacity (FC) and 55% FC. Results indicated that different scions were affected differently by drought stress. ‘Pink Lady’ had higher net photosynthetic rate (P _N), stomatal conductance (g _s), and transpiration rate (E) compared with ‘Qinguan’ under both water treatments. However, ‘Qinguan’ had lower minimal fluorescence (F₀), higher maximum fluorescence (F_m), and higher maximum photochemical efficiency of photosystem II (F_v/F_m) than ‘Pink Lady’ at 55% FC. Moreover, ‘Qinguan’ had larger shoot dry mass (ShDM) and higher intrinsic WUE_I than ‘Pink Lady’ under both water status. Gas-exchange and growth parameters, except for P _N and scion diameter, were significantly affected by the cultivar and water treatment. At 70% FC, ShDM was significantly correlated with WUE_I. Moreover, WUE_I was negatively linearly correlated with g _s at either 70 or 55% FC. These results might indicate that ‘Pink Lady’ was more sensitive to drought than ‘Qinguan’. ‘Qinguan’ apple was able to improve WUE more than ‘Pink Lady’ under both well-watered and drought conditions. The growth parameters and photosynthetic capacity of two different scions showed that the combination of double scion-one rootstock might eliminate the influences of the rootstock and pot size.     

Water use efficiency, transpiration and net CO2 exchange of four alfalfa genotypes submitted to progressive drought and subsequent recovery

The predicted worldwide increase in arid areas and water stress episodes will strongly affect crop production. Plants have developed a wide diversity of physiological mechanisms for drought tolerance. A decline in photosynthesis and thus yield production is a common response to drought, as are increases in the water use efficiency of photosynthesis (WUE_ph) and productivity (WUE_p). The aim of our study was to determine the physiological effects (especially WUE_ph and WUE_p) of progressive drought and subsequent recovery in three cultivars adapted to a Mediterranean climate [Tafilalet (TA), Tierra de Campos (TC), and Moapa (MO)], and another representative from an oceanic climate (Europe (EU)). The accuracy of the relationships between WUE_ph or WUE_p and carbon isotope discrimination (Δ ¹³C) in shoots was also investigated as a function of water stress intensity. Mild drought (7 days of water withholding) decreased the net CO₂ exchange (A), leaf conductance to water (g) and transpiration in EU leading to an increased WUE_ph. Δ ¹³C was correlated with WUE_p but not with WUE_ph, probably due to a late decrease in g. After moderate drought (14 days), A and g decreased in all cultivars, increasing WUE_ph. In this period WUE_p also increased. Both WUE parameters were correlated with Δ ¹³C, which may indicate that the g value at the end of moderate water stress was representative of the growing period. After 21 days, TA was the most productive cultivar but under severe drought conditions there was no difference in DM accumulation among cultivars. After the recovery period, leaf area was increased but not total DM, showing that leaves were the most responsive organs to rewatering. Severe water stress did not decrease WUE_ph or WUE_p, and Δ ¹³C did not increase after recovery. This absence of a response to severe drought may indicate significant effects on the photosynthetic apparatus after 21 days of withholding water. As for mild drought, WUE_p but not WUE_ph was correlated with Δ ¹³C, supporting the view that WUE_p is a more integrative parameter than WUE_ph.