红砂幼苗根系形态特征和水分利用效率对土壤水分变化的响应

为探讨干旱与半干旱区受损红砂种群幼苗适宜生长的土壤水分条件,采用盆栽方法,研究了红砂幼苗在充分灌溉(FI)、适度灌溉(MI)、干旱处理(DT)3个水分处理下根系形态和水分利用效率的变化特征。结果表明:(1)红砂幼苗根系形态因水分条件和根序的不同而各异;随灌溉量的减少红砂幼苗根系直径和根体积均表现为FIMIDT,但干旱处理促进了根系的伸长生长和比表面积和比根长增加,根系形态的可塑性是红砂幼苗获取水分适应干旱环境的重要策略之一。(2)随根序的升高,各处理水平下红砂幼苗根长、比根长均显著减少,而其根直径和体积却显著增加,表明红砂幼苗根系内部具有高度的形态异质性。(3)与FI处理相比,MI和DT处理下红砂幼苗根系总生物量分别增加了50.00%、19.23%,但MI和DT处理却显著降低了红砂幼苗地上生物量,特别是叶片生物量下降幅度最大,分别降低了62.15%、83.28%,导致根冠比随灌溉量的减少而逐渐增加。(4)干旱处理显著提高了红砂幼苗的水分利用效率。研究认为,在灌溉量减少的情况下,红砂幼苗可通过根长、根系表面积和体积、直径等形态变化来优化其空间分布构型,以调节植株对水分的利用,提高水分利用效率。     

根源信号参与调控气孔行为的机制及其农业节水意义

在土壤干旱情况下,根源信号一方面向植物地上部分的长距离传输,为地上部分提供了土壤水分获取能力的测度,另一方面调控气孔开度,抑制蒸腾作用并提高植物的水分利用效率．文中综述了根源信号参与调控植物水分利用的生理机制和理论模型,指出该模型与根系吸水模型、气孔导度模型耦合,能够更好地反映植物叶片对土壤干旱以及大气干旱的响应、评述了在根源信号参与调控植物水分关系的基础上发展的调亏灌溉(RDI)、部分根系干旱(PRD)和控制性交替灌溉(CAI)等有效灌溉手段,有助于合理配置根系层供水量,通过根土相互作用和信号物质的传输,降低蒸腾和提高水分利用效率、另外,根源信号在调控根系生长发育、延缓地上部分生长以调节根冠比例,优化资源分配以利于生殖生长等方面均有所为,为全面提高农田水分利用效率提供节水生理基础。     

土壤干旱胁迫对黄栌叶片光合作用的影响

采用CIRAS-2型便携式光合作用系统,设置充足供水、轻度、中度和重度胁迫4种土壤水分处理,研究土壤干旱和强光胁迫对3年生黄栌苗木叶片光合作用的影响.结果表明:土壤干旱胁迫对黄栌叶片的光合性能参数影响显著,随着土壤水分胁迫的加剧,黄栌叶片的光合速率、蒸腾速率和光量子效率明显降低,光补偿点增高,水分利用效率在轻度水分胁迫(土壤相对含水量60%～65%)下最高;在强光(有效辐射强度1000～1800μmol.m-2.s-1)范围内,叶片光合速率和水分利用效率均较高,而对弱光的光能吸收和光量子效率较低,并随土壤水分胁迫加剧明显下降.     

不同节水灌溉方式对干旱山地板栗生长结实的影响

在山东省泰安市半干旱、半湿润气候区的山地果园,以板栗为试材,研究了陶罐贮水、蓄水穴和畦灌覆盖3种节水灌溉方式下栗园土壤水分特征及对板栗根系、树体生长和结实的影响.结果表明：与畦灌(对照)相比,3种节水灌溉方式均能延长果园土壤保湿时间,其中陶罐贮水处理效果最明显,保湿时间长达32 d,较对照延长13 d.节水处理下,板栗结果枝长度和数量、叶片面积和质量、果前梢混合芽数量等均较对照明显增加.陶罐贮水和蓄水穴处理能对深层土壤根系进行灌溉并诱导深层根系生长,降低了浅层干旱对根系的胁迫.3种节水灌溉均能大幅度提高板栗果实产量,陶罐贮水、蓄水穴和畦灌覆盖处理的产量分别较对照提高18.8%、16.5%和14.2%.     

土壤水分梯度对白三叶(Trifolium repens)光合作用和根系分布的影响

通过对两个品种白三叶Trifolium repens cv.Haifa(海发)和Trifolium repens cv.Rivendel(瑞文德)盆栽试验,模拟3种不同的土壤水分状况(无水分胁迫:保持植株良好的水分供应;轻度胁迫:表层0～20cm土壤处于干旱状态;重度胁迫:表层0～20cm土壤处于极干旱状态,20～40cm土壤处于干旱状态)对白三叶光合作用和根系生长的影响.结果表明,当植株未遭受水分胁迫时,两个品种白三叶的光合作用和根系生长状况没有明显差异;当表层0～20cm处于干旱状态时,'海发'在处理后期的净光合速率和水分利用效率升高,根系生长量增大,表现出促进作用,'瑞文德'受到的影响不显著;当表层0～20cm处于极干旱、20～40cm处于干旱状态时,'海发'在处理前期受到轻微影响,随后恢复正常状态,'瑞文德'则受到较严重的影响.随着干旱程度的加深和时间的延长,白三叶的根冠比逐渐增大.与'瑞文德'相比,在相同时期相同胁迫程度下,'海发'的根冠比没有显著差异,但深根数量大大超过'瑞文德',因而,'海发'的耐旱能力强于'瑞文德'.     

山黧豆根系对H2O2诱导氧化胁迫的生理应答

以水培7d苗龄的山黧豆幼苗为材料,向水培溶液中施加不同浓度H2O2处理山黧豆幼苗24h,分析山黧豆根系受氧化胁迫的程度与抗氧化系统的应答特征,以揭示山黧豆对氧化胁迫的耐受机制。结果显示:(1)随外源H2O2处理浓度的不断增加,山黧豆幼苗侧根的数目无显著变化,而其根的鲜重则显著降低。(2)同时,根系组织的内源H2O2染色范围和程度显著增高,但根尖区域始终保持较低水平的H2O2;相反,O-·2染色范围和程度明显减少,根尖区域却始终保持较高水平的O-·2。(3)同期根系抗坏血酸(ASC)含量及过氧化氢酶(CAT)、过氧化物酶(POD)与抗坏血酸过氧化物酶(APX)的活性均表现出了先升高后降低的趋势,而超氧化物歧化酶(SOD)一直表现为持续上升的趋势。研究表明,在外源H2O2胁迫条件下,山黧豆根系O-·2的积累可能与其生长和活力呈正相关,而根系H2O2的积累则与其受氧化胁迫程度呈正相关;低浓度的H2O2处理可以提高山黧豆抗氧化系统对体内活性氧的清除能力。     

胡杨幼苗根系生长与构型对土壤水分的响应

胡杨实生幼苗成活率低是制约其更新与人工育苗保存的关键问题,而幼苗根系生长与构型是影响其存活的重要因素。该试验以1年生胡杨幼苗为材料,通过2种给水方式(断续给水和连续给水)下各6个土壤水分梯度处理的控制试验,探究胡杨幼苗根系生长与构型对荒漠地区关键因子水分的响应特征。结果表明:(1)2种给水方式下干旱胁迫均使根冠比增加,且断续给水处理下幼苗根冠比显著大于连续给水。(2)一定程度的干旱处理还可以促进幼苗根系形态发育特征的发展和根系生物量的积累,但过度干旱胁迫或土壤水分含量过多都会抑制根系生长,并以连续给水、土壤含水量15%处理下幼苗根系最为发达。(3)幼苗深扎根能力强,其根宽深比在2种给水方式下均小于1,且断续给水处理显著小于连续给水处理;2种给水方式下根宽深比都与土壤水分含量呈显著正相关。(4)根系拓扑指数在2种给水方式下无显著差异且均接近1,但都与土壤水分含量呈显著负相关。即幼苗根系趋向鱼尾状分支结构,次级分支少,这种根系延伸策略有利于胡杨幼苗在干旱贫瘠的土壤环境中生存。(5)根系构型参数的主成分分析显示,总根长、总根表面积、根宽深比和拓扑指数在2种给水方式下都能很好地表示胡杨幼苗根系构型特征。可见,胡杨幼苗根系通过构筑鱼尾状分支结构、增加垂直根纵向延伸能力和增大根冠比适应干旱环境;水分对于胡杨幼苗根系生长与构型作用显著,根系对水分因子的响应对于胡杨幼苗适应水分异质性环境具有重要意义。     

模拟贝壳砂水分变化对旱柳光合特性的影响

为探讨贝壳堤岛旱柳叶片光合特性的水分响应规律,以2 a生旱柳苗木为材料,模拟设置贝壳砂生境系列水分梯度,测定分析不同土壤水分条件下旱柳叶片的主要光合生理参数。结果表明:（1）直角双曲线修正模型可较好模拟旱柳叶片净光合速率的光响应过程,维持旱柳较高光合作用的土壤相对含水量（RWC）为50.1%～94.4%,适宜光强为800～1 600 μmol·m^-2·s^-1,水分对光强利用的补偿效应显著。（2）随土壤水分的降低,旱柳叶片净光合速率、光饱和点、表观量子效率及最大净光合速率均表现为先升高后降低;干旱和渍水胁迫条件下,旱柳叶片的光补偿点升高,光饱和点降低,光照生态幅变窄,光能利用效率降低,水分胁迫抑制光能效应明显。（3）随土壤水分的降低,旱柳叶片瞬时和潜在水分利用效率均表现为先升高后降低,分别在RWC为45.7%、40.6%时达到最大值,适度干旱胁迫可显著提高旱柳叶片的水分利用效率。（4）干旱和渍水胁迫均显著降低旱柳叶片的叶绿素含量和叶片水势,随土壤水分降低两者均表现为先升高后降低,叶绿素含量和叶片水势分别在RWC为58.9%、50.1%达到最高值。研究发现,贝壳砂生境旱柳叶片光合生理参数对土壤水分表现出一定的阈值响应,维持旱柳较高光合能力和水分利用效率的适宜土壤水分相对含量为50.1%～77.7%,表现为耐水湿不耐干旱的水分特性。     

松土对干旱胁迫下油橄榄抗性生理及土壤环境因子的影响

以田间树龄6~7年的油橄榄树为对象,设置充分灌溉(W_(CK))、2/3灌溉量(W_1)、1/3灌溉量(W_2)3个土壤水分环境条件,考察松土对干旱胁迫下油橄榄根际土壤理化指标、土壤酶活性、油橄榄叶片抗性生理及根系活力的影响,探究松土提高油橄榄抗旱性的生理机制,为油橄榄的抗旱生产提供理论和技术支持。结果表明:(1)随着灌溉量的减少,油橄榄叶片O~-·_2产生速率、MDA含量和H_2O_2含量都有所增加,油橄榄叶片受到了干旱造成的氧化胁迫,但松土处理均抑制了O~-·_2产生速率、MDA含量和H_2O_2含量的增长,同时也缓解了细胞膜稳定指数的下降;(2)经松土处理后,除SOD活性和还原型谷胱甘肽含量增加不明显外,油橄榄叶片POD活性、CAT活性均比不松土处理显著增加,增强了其抵御氧化胁迫的能力;(3)松土处理使油橄榄根际土壤相关酶活性、根际土壤含水量有所增加,但土壤pH值有所降低,这些根际土壤环境因子的变化对于油橄榄的矿质营养和水分状况的改善都具有积极的作用,尤其在因灌溉不足引起干旱胁迫的情形下更为重要。(4)松土处理提高了油橄榄叶片叶绿素含量和根系活力。研究认为,松土处理通过改善干旱胁迫下油橄榄的根际微环境条件,强化油橄榄叶片的酶促和非酶促抗氧化系统活性,提高自身渗透调节能力,增强根系活力,从而有效提高油橄榄对干旱的整体抗性。     

水分胁迫下山黧豆多胺代谢与 β-N-草酰-L-α ,β-二氨基丙酸积累相关性的研究

为了研究水分胁迫下山黧豆 (LathyrussativusL .)叶片中多胺代谢与 β_N_草酰_L_α,β_二氨基丙酸 (ODAP)积累的相关关系 ,利用聚乙二醇 (PEG)对山黧豆幼苗进行水分胁迫处理 ,同时加入腐胺 (Put) ,α_二氟甲基精氨酸(DFMA)和Put DFMA。实验结果表明 ,随PEG处理时间的延长 ,山黧豆幼苗叶片中Put、亚精胺 (Spd)和精胺 (Spm)含量逐渐增加 ,特别是Spm含量增加显著 ,同时ODAP逐渐积累 ;在PEG处理的同时 ,加入Put使得Put、Spd含量显著增加 ,但对Spm影响不大 ,同样对ODAP含量影响也较小 ;加入DFMA可显著抑制Put、Spd、Spm的积累 ,同时也抑制了ODAP的积累 ;加入Put DFMA ,Put可以部分地减缓DFMA对两种内源多胺 (Put和Spd)合成的抑制作用 ,但对Spm所受DFMA的抑制作用影响不大 ,这时ODAP的积累也受到抑制。由此可见 ,水分胁迫对山黧豆幼苗叶片中多胺特别是Spm含量的增加与ODAP的积累密切相关。     

Measurement and modelling of ABA signalling in potato (Solanum tuberosum L.) during partial root-zone drying

The objective of this study was to develop a simple mechanistic model to predict the magnitude of ABA signalling ([X-ABA]) of potatoes (Solanum tuberosum L.) exposed to partial root-zone drying (PRD). Potatoes were grown in pots in a glasshouse with the roots split equally between two soil columns. At tuber initiation stage, plants were subjected to three irrigation treatments: (1) both soil columns were fully irrigated (FI) daily to a volumetric soil water content (θ) of 18.0%; (2) PRD, in which one soil column was irrigated daily to 18.0% while the other was allowed to dry, and the irrigation was shifted between columns when the θ of the drying soil column had decreased to 7–8%; (3) non-irrigation (NI), where irrigation was withheld after onset of treatments and lasted for 5 days until θ had decreased to 7%. In the PRD plants, the fraction of soil water extraction (FSWE) by the dry roots declined exponentially with declining soil water potential (Ψ_soil-dry); however, after shifting of irrigation, the previously dried roots immediately recovered the full capacity of water uptake. During the first PRD drying cycle, FI plants had the highest stomatal conductance (g_s), and followed by PRD plants and NI plants had the lowest g_s. Photosynthesis (A) was similar for FI and PRD plants, and was significantly lower for the NI plants only on 3–4 days after treatment. In the NI plants, a linear relationship between Ψ_soil and [X-ABA] was obtained. Based on these relationships, a simple model predicting [X-ABA] in the PRD plants ([X-ABA]_PRD) was developed. Assuming that a constant [X-ABA] of 115 nM (similar to that found in the FI plants) originated from the wet roots; the simulation results indicated that irrigation should be shifted between the two sides when Ψ_soil-dry had decreased to −80 kPa, and [X-ABA]_PRD had reached a peak of ca. 150 nM. However, the [X-ABA]_PRD predicted by the model was significantly lower than the measured value; whilst a simple average of [X-ABA] from the wet and the dry soil columns based on the [X-ABA]–Ψ_soil relationship better predicted [X-ABA]_PRD.     

Physiological responses of potato (Solanum tuberosum L.) to partial root-zone drying: ABA signalling, leaf gas exchange, and water use efficiency

The physiological responses of potato (Solanum tuberosum L. cv. Folva) to partial root-zone drying (PRD) were investigated in potted plants in a greenhouse (GH) and in plants grown in the field under an automatic rain-out-shelter. In the GH, irrigation was applied daily to the whole root system (FI), or to one-half of the root system while the other half was dried, for 9 d. In the field, the plants were drip irrigated either to the whole root system near field capacity (FI) or using 70% water of FI to one side of the roots, and shifted to the other side every 5-10 d (PRD). PRD plants had a similar midday leaf water potential to that of FI, whereas in the GH their root water potential (Psi(r)) was significantly lowered after 5 d. Stomatal conductance (g(s)) was more sensitive to PRD than photosynthesis (A) particularly in the field, leading to greater intrinsic water use efficiency (WUE) (i.e. A/g(s)) in PRD than in FI plants on several days. In PRD, the xylem sap abscisic acid concentration ([ABA](xylem)) increased exponentially with decreasing Psi(r); and the relative [ABA](xylem) (PRD/FI) increased exponentially as the fraction of transpirable soil water (FTSW) in the drying side decreased. In the field, the leaf area index was slightly less in PRD than in FI treatment, while tuber biomass was similar for the two treatments. Compared with FI, PRD treatment saved 30% water and increased crop water use efficiency (WUE) by 59%. Restrictions on leaf area expansion and g(s) by PRD-induced ABA signals might have contributed to reduced water use and increased WUE.     

Water relations and gas exchange in olive trees under regulated deficit irrigation and partial rootzone drying

It is widely believed that partial root drying (PRD) reduces water losses by transpiration without affecting yield. However, experimental work carried out to date does not always support this hypothesis. In many cases a PRD treatment has been compared to a full irrigated treatment, so doubt remains on whether the observed benefits correspond to the switching of irrigation or just to PRD being a deficit irrigation treatment. In addition, not always a PRD treatment has been found advantageous as compared to a companion regulated deficit irrigation (RDI) treatment. In this work we have compared the response of mature ‘Manzanilla‘ olive trees to a PRD and an RDI treatment in which about 50% of the crop evapotranspiration (ET_c) was supplied daily by localised irrigation. We alternated irrigation in the PRD treatment every 2 weeks in 2003 and every 3 weeks in 2004. Measurements of stem water potential (Ψ_stem), stomatal conductance (g _s) and net CO₂ assimilation rate (A) were made in trees of both treatments, as well as in trees irrigated to 100% of ET_c (Control trees) and in Rain-fed trees. Sap flow was also measured in different conductive organs of trees under both PRD and RDI treatments, to evaluate the influence of alternating irrigation on root water uptake and tree water consumption. We found small and random differences in Ψ_stem, g _s and A, which gave no evidence of PRD causing a positive effect on the olive tree performance, as compared to RDI. Stomatal conductance decreased in PRD trees as compared to Control trees, but a similar decrease in g _s was also recorded in the RDI trees. Sap flow measurements, which reflected water use throughout the irrigation period, also showed no evidence of g _s being more reduced in PRD than in RDI trees. Daily water consumption was also similar in the trees of the deficit irrigation treatments, for most days, throughout the irrigation period. Alternating irrigation in PRD trees did not cause a change in either water taken up by main roots at each side of the trees, or in the sap flow of both trunk locations and main branches of each side. Results from this work, and from previous work conducted in this orchard, suggest that transpiration is restricted in trees under deficit irrigation, in which roots are left in drying soil when water is applied by localised irrigation, and that there is no need to alternate irrigation for achieving this effect. Section Editor: R. E. Munns     

Water relations,photosynthesis, growth and water-use efficiency in tomato plants subjected to partial rootzone drying and regulated deficit irrigation

Abstract

Partial rootzone drying (PRD) and regulated deficit irrigation (RDI) are water-saving irrigation systems that have been developed to increase water-use efficiency (WUE) without significant yield reduction. In order to investigate whether a high-value horticultural crop such as tomato responded differently to RDI and PRD, we compared the physiological and growth responses of tomato plants using a split-root system. Plants were grown in a greenhouse under controlled conditions with their roots separated equally between two soil compartments. Three irrigation treatments were imposed: (i) Control, receiving an amount of water equivalent to 100% of plant transpiration; (ii) PRD, in which one compartment was watered with 50% of the amount of water supplied to the controls, allowing one-half of the root system to be exposed to dry soil and switching irrigation between sides weekly; and (iii) RDI, in which 50% of the amount of water given to the controls was supplied, half to each side of the root system. Leaf RWC and midday leaf Ψ decreased substantially in RDI-treated plants, while the PRD plants exhibited relatively higher Ψ and RWC values. Both PRD and RDI treatments reduced by about 30% the total plant dry mass compared with the control. However, plant transpiration was reduced by about 50% in both PRD and RDI, allowing a significant improvement in whole-plant WUE. Stomatal conductance (Gs) and leaf growth were also significantly reduced by PRD and RDI. These results may be related to a significant increase in xylem sap pH and leaf apoplastic pH. Generally, the photosynthetic apparatus of tomato leaves had a high resistance to restricted water availability. In fact, the decreased Gs had no major negative impact on carbon assimilation. However, V _cmax, i.e. Rubisco efficiency, was significantly decreased in RDI plants with respect to control ones. This may imply that, although the differences between the PRD and RDI treatments in our study were subtle, they may become more marked with a more prolonged and severe water deficit.     

Changes in antioxidant activities and phenol content in tomato plants subjected to partial root drying and regulated deficit irrigation

Abstract

Partial rootzone drying (PRD) and regulated deficit irrigation (RDI) are water saving irrigation systems that have been developed to increase water use efficiency (WUE) without significant yield reduction. To examine whether tomato responded differently to RDI and PRD, we compared the changes in antioxidative defenses in tomato plants using a split-root system. Tomato plants were grown for 21 days under controlled conditions with their roots separated equally between two soil compartments. Three irrigation treatments were imposed: Control, receiving an amount of water equivalent to 100% of plant transpiration; PRD in which one compartment was watered with 50% of the amount of water supplied to the controls, allowing one-half of the root system to be exposed to dry soil, and switching irrigation between sides weekly; RDI in which 50% of the amount of water given to the controls was supplied, half to each side of the root system. Relative water content (RWC), midday leaf Ψ and chlorophyll content decreased largely in RDI-treated plants, whereas the PRD plants exhibited relatively higher Ψ and RWC values. An enhanced level of lipid peroxidation in both roots and leaves indicated that PRD and RDI caused oxidative stress in tomato plants. In leaves, superoxide dismutase (SOD), soluble peroxidase (POX) and polyphenol oxidase (PPO) activities showed an increase in the early phase of water deficit, and then decreased in the remaining phase of the drying cycle. However, the increase was more pronounced under RDI. Catalase (CAT) activity declined continuously from the onset of PRD and RDI treatments to below the control level, and the reduction was less under PRD than RDI. POX cell-wall associated activities exceeded the control level by 450% and 230%, respectively, under RDI and PRD. At the root level, while CAT activity also decreased under both PRD and RDI, the activities of SOD, POX and PPO significantly increased and their activities showed an alternating increase/decrease paralleling the alternating irrigation in PRD-treated roots. As a result of the difference in POX and PPO activities between the two water treatments applied, PRD-treated plants accumulated more soluble and cell-wall bound phenolic compounds.     

Water relations, activities of antioxidants, ethylene evolution and membrane integrity of pigeonpea roots as affected by soil moisture

The plants of pigeonpea (Cajanus cajan L.) cv. H77-216 were subjected to moderate [soil moisture content (SMC) = 7.3 ± 0.5 %] and severe (SMC = 4.3 ± 0.5 %) drought by withholding the irrigation at vegetative stage (45 d after sowing). The control plants were maintained at SMC of 11.0 ± 0.5 %. Half of the stressed plants were re-irrigated and their recovery was studied after 2 d. Leaf water potential, osmotic potential, and relative water content of leaf and root decreased significantly while a sharp rise in proline and total soluble sugars contents were noticed. Drought induced a significant increase in 1-aminocyclopropane 1-carboxylic acid (ACC) content and ACC oxidase activity which caused a considerable increase in ethylene evolution. Malondialdehyde content and relative stress injury were increased under drought whereas reverse was true for ascorbic acid content. The membrane integrity of roots decreased during stress and recovered on rehydration. The specific activity of total superoxide dismutase, ascorbate peroxidase, glutathione reductase, and glutathione transferase decreased to 37 – 78 %, 17 – 62 %, 29 – 36 % and 57 – 79 % at moderate and severe drought, respectively. The increase in activity of catalase and peroxidase could not overcome the accumulation of H₂O₂ content in the roots.     

基于容器分区处理探究黑麦草生长对喀斯特不同土壤生境和水分的响应

为了探究不同水分条件下喀斯特地区分布不均、厚薄不一土壤小生境对禾本科草本植物生长的影响,用3种不同深度的容器(对照深度CK,深土D和浅土S)两两组合为6种复合容器(CK-CK、CK-S、CK-D、D-D、S-D和S-S)以实现容器分区,研究了黑麦草的根系生长、生物量积累及其分配特征。结果表明:1)在水分充足(W_0)条件下,组合了浅土容器和深土容器的处理中,黑麦草的根系生长(根长、根直径、根表面积和根生物量)均低于对照容器(CK-CK),且有浅土容器的组合处理(S-S,S-D,CK-S)受抑制程度大于有深土容器的组合处理(CK-D,D-D);当水分含量降低后,即中水(W_1)和低水(W_2)条件下,有深土容器的组合[D-D和(或)CK-D]根系生长与对照相比显著增加,而有浅土容器的组合[S-S和(或)CK-S]根系生长与对照相比显著降低。2)对比同一处理不同容器分区中黑麦草生长指标发现,在水分充足情况下,深土容器和浅土容器均会抑制植物生长,而当水分减少,S区根系生长被严重抑制,但D区根系增长优势明显。3)水分充足条件下,根冠比未受到显著影响;当水分降低时,组合了深土容器的处理根冠比均有升高的趋势,组合了浅土容器的处理根冠比有降低趋势。由此可见,不同土壤生境带来的物理空间限制会影响植物根系生长和生物量积累与分配,但水分的减少会改变根系生长及生物量积累对不同土壤生境的响应:在水分充足时,土壤物理空间是影响根系生长和生物量积累与分配的主要因子,黑麦草主要发展浅层根系。而当水分减少时,黑麦草根系在浅层土壤中无法获取供给生长代谢活动的足量水分,更倾向于将有限的有机物分配给根,通过根系伸长、表面积和体积增大、直径增粗等策略加强水分吸收,从而增强对干旱的抗逆性,提高对土壤和水分异质性的适应。     

Deficit irrigation in grapevine improves water-use efficiency while controlling vigour and production quality

Grapevine irrigation is becoming an important practice to guarantee wine quality or even plant survival in regions affected by seasonal drought. Nevertheless, irrigation has to be controlled to optimise source to sink balance and avoid excessive vigour. The results we present here in two grapevine varieties (Moscatel and Castelão) during 3 years, indicate that we can decrease the amount of water applied by 50% (as in deficit irrigation, DI, and in partial root drying, PRD) in relation to full crop's evapotranspiration (ETc) [full irrigated (FI) vines] with no negative effects on production and even get some gains of quality (in the case of PRD). We report that in non-irrigated and in several cases in PRD vines exhibit higher concentrations of berry skin anthocyanins and total phenols than those presented by DI and FI vines. We showed that these effects on quality were mediated by a reduction in vigour, leading to an increase on light interception in the cluster zone. Because plant water status during most of the dates along the season was not significantly different between PRD and DI, and when different, PRD even exhibited a higher leaf water potential than DI vines, we conclude that growth inhibition in PRD was not a result of a hydraulic control. The gain in crop water use in DI and PRD was accompanied by an increase of the δ¹³C values in the berries in DI and PRD as compared to FI, suggesting that we can use this methodology to assess the integrated water-use efficiency over the growing season.     

Drought‐related tree death of savanna eucalypts: Species susceptibility,soil conditions and root architecture

Questions: For eucalypt savanna in northeast Australia subject to multi‐year rainfall deficits this paper asks whether (1) dominant tree species (Ironbarks, Boxes) are more drought susceptible than the sub‐dominant Bloodwoods; (2) whether soil moisture is beyond wilting point in surface soil layers but available at depth; (3) soil conditions (moisture availability and texture) are related to tree death during drought; (4) the root systems of the Boxes and Ironbarks are shallower than the Bloodwoods; and the survivors of drought within species have deeper root systems than those that died. Location: Central Queensland, Australia. Methods: Patterns of tree death between eucalypt species were compared from field data collected after drought. Soil conditions during drought were described and compared with patterns of tree death for the Ironbark Eucalyptus melanophloia. The basal area and orientation of coarse roots were measured on upturned trees after broad‐scale tree clearing, and compared between species, and between live and dead trees with tree size as a covariate. Results: Drought‐induced tree death was higher for dominant Ironbark‐Box than for sub‐dominant Bloodwoods. During a moderate to severe drought in 2004, 41% of 100 cm deep subsoils had soil matric potential less than‐5600 kPa. The drought hardy Bloodwoods had a greater root basal area and particularly so for vertical roots compared to the drought sensitive Ironbark‐Box. Within species there was no significant difference in root basal area characteristics between trees that were recently killed by drought and those that remained relatively healthy. Surface soil moisture availability was lower where tree densities were high, and tree death increased as surface soil moisture became less available. Tree death was also greater as the clay content of sub‐soils increased. Discussion: The study suggests species with roots confined to upper soil layers will suffer severe water stress. The results strongly indicate that root architecture, and the way it facilitates water use during drought, is important for the relative dominance of the tree species. Patchiness in drought‐induced tree death seems to be at least partially a product of heterogeneity in sub‐soil conditions and competition for soil moisture.