Root growth and water uptake in winter wheat under deficit irrigation

Root growth is critical for crops to use soil water under water-limited conditions. A field study was conducted to investigate the effect of available soil water on root and shoot growth, and root water uptake in winter wheat (Triticum aestivum L.) under deficit irrigation in a semi-arid environment. Treatments consisted of rainfed, deficit irrigation at different developmental stages, and adequate irrigation. The rainfed plots had the lowest shoot dry weight because available soil water decreased rapidly from booting to late grain filling. For the deficit-irrigation treatments, crops that received irrigation at jointing and booting had higher shoot dry weight than those that received irrigation at anthesis and middle grain filling. Rapid root growth occurred in both rainfed and irrigated crops from floral initiation to anthesis, and maximum rooting depth occurred by booting. Root length density and dry weight decreased after anthesis. From floral initiation to booting, root length density and growth rate were higher in rainfed than in irrigated crops. However, root length density and growth rate were lower in rainfed than in irrigated crops from booting to anthesis. As a result, the difference in root length density between rainfed and irrigated treatments was small during grain filling. The root growth and water use below 1.4 m were limited by a caliche (45% CaCO₃) layer at about 1.4 m profile. The mean water uptake rate decreased as available soil water decreased. During grain filling, root water uptake was higher from the irrigated crops than from the rainfed. Irrigation from jointing to anthesis increased seasonal evapotranspiration, grain yield, harvest index and water-use efficiency based on yield (WUE), but did not affect water-use efficiency based on aboveground biomass. There was no significant difference in WUE among irrigation treatments except one-irrigation at middle grain filling. Due to a relatively deep root system in rainfed crops, the higher grain yield and WUE in irrigated crops compared to rainfed crops was not a result of rooting depth or root length density, but increased harvest index, and higher water uptake rate during grain filling.     

有限灌溉条件下冬小麦水分亏缺的灵敏度分析

水分亏缺是干旱、半干旱区作物生产的最主要限制因子。在我国西北半干旱区,随着集水生态农业的发展．实施在作物生育期对其进行关键性的有限灌溉．这就使得更多的土地具有种植价值了。用一个度量作物不同生长阶段水分亏缺的灵敏度指标值λ来确定灌溉关键期。对一个给定的作物．在不同的生长阶段．λ的值是不同的,λ的值越大．生长阶段对水分越灵敏,水分亏缺对产量造成的危害越大,从而越需要保持水分平衡。在西北半干旱区甘肃省定西农业试验站,经过两年冬小麦种植试验,建立了冬小麦产量-耗水量Jensen模型,该模型表明拔节期以后．λ值明显增大．至抽穗期达最大,这说明从拔节期开始．该地冬小麦进入灌溉关键期．抽穗期是灌溉的最关键时期。一个理论方法应用到有限灌溉试验田．确定了灌溉水减少与经济效益的关系,结果表明在作物生育期,一些水分减少是可能的。用Nairizi和Rydzewski的方法计算出的λ值确定出的最大允许水分亏缺是不合理的高,它们计算λ值的方法在半干旱区是不适用的,用我们建立的模型计算出的最大允许水分亏缺比较合理,在效益成本比为1．5时,冬小麦允许的水分亏缺是12．4％．这与大田试验较为接近。     

Photosynthetic characteristics of peanut genotypes under excess and deficit irrigation during summer

Physiology and Molecular Biology of Plants - In a field experiment three irrigation treatments were given to twelve peanut genotypes through drip. At 80 days after sowing (DAS) the amount...     

Grapevine acclimation to water deficit: the adjustment of stomatal and hydraulic conductance differs from petiole embolism vulnerability

Planta - Drought-acclimated vines maintained higher gas exchange compared to irrigated controls under water deficit; this effect is associated with modified leaf turgor but not with improved...     

Effects of regulated deficit irrigation under subsurface drip irrigation conditions on water relations of mature almond trees

Plant and Soil - The influence of several regulated deficit irrigation (RDI) strategies under subsurface drip irrigation (SDI) conditions on water relations and gas exchange activity was analysed...     

有限供水下冬小麦全程耗水特征定量研究

为明确冬小麦不同水分条件下全生育过程日耗水及阶段耗水特征,在北京地区利用蒸渗仪系统连续监测了几种灌溉处理(W4:起身水+孕穗水+开花水+灌浆水;W2:拔节水+开花水;W1:拔节水;W0:无灌水)耗水动态变化。结果表明:冬小麦全生育期的耗水动态可分为3个阶段:(1)播种至11月底的冬前阶段,这个阶段日耗水量波动明显,一般低于3 mm/d;(2)12月上旬至来年2月底的冬季阶段,这个阶段日耗水量低于0.4 mm/d,且波动很小;(3)3月初小麦返青至收获的春后生长阶段,这个阶段日耗水量总体上是一个先升高后降低的过程,但波动很大,每次灌水都会引起1个日耗水高峰的出现。耗水日变化呈单峰或双峰曲线,高峰出现在正午前后,高峰值因灌水处理而有明显差异,灌水多则耗水峰值显著升高,而夜间耗水量及其在不同处理间差异均很小。拔节至成熟期是冬小麦耗水的主要时期,该期耗水占总耗水60%以上。减少灌溉会增加土壤贮水消耗,但降低了总耗水量。综合比较表明,在有限灌溉下,拔节水和开花水组合是高产和高水分效率相统一的灌溉模式。     

Effects of regulated deficit irrigation under subsurface drip irrigation conditions on vegetative development and yield of mature almond trees

Plant and Soil - The influence of several regulated deficit irrigation (RDI) strategies, applied under subsurface drip irrigation (SDI), on vegetative development and yield parameters in mature...     

Distribution of newly fixed C-photoassimilate under deficit irrigation and half-root stress in peach trees

Two-year-old potted peach ‘Zaojiubao’ (Prunus persica L. Batsch) trees on wild P. persica rootstock were subjected either to regulated deficit irrigation (RDI), in which trees were water stressed during fruit pit hardening (stage II) followed by rewatering during the final rapid fruit growth stage (stage III), or to half-root stress (HRS) treatments during the same two stages. To investigate the allocation of carbon assimilates among sink organs, shoots were fed with ¹⁴CO₂ twice, either during stage II or stage III. The distribution coefficient (K) represented the competitive sink strength. RDI and HRS induced an altered allocation pattern of ¹⁴C-assimilates. The import to shoot apexes was reduced. However, there were no significant reduction in fruit diameter and weight. Moreover, the Ks of the fruit subparts of RDI and HRS treated trees were similar to or sometimes higher than those of CK trees. There were more ¹⁴C-assimilates and higher K values of seeds from RDI trees during stage III compared with CK. In addition, stressed roots seemed to have stronger abilities to attract ¹⁴C-assimilates. It is concluded that RDI and HRS resulted in a decreased sink activity in the shoot and a change of carbon allocation toward stressed roots and seeds without negative effects on fruit growth.     

Stress tolerance in flax plants inoculated with Bacillus and Azotobacter species under deficit irrigation

Drought stress affects not only crop growth but also its morpho-physiological and biochemical traits to reduce crop productivity. The study reported in this article was designed and implemented to determine the effects of deficit irrigation and bacterial inoculation on flax plants. For this purpose, seeds were inoculated with Bacillus amyloliquefaciens (B₁), Bacillus sp. Strain1 (B₂), and Azotobacter chroococcum (A) as plant growth promoting rhizobacteria (PGPR). The individual inoculated plants were then grown under field conditions in 2015, while individually and in combination in pots in 2016. The irrigation regimes in either experiments included 50, 75 and 100% crop water requirement. Bacterial cultures were observed to produce ammonia (except B₂), indole acetic acid and siderophores. Results showed that the PGPRs significantly mitigated the effects of water deficit. Compared with the control plants, the bacterially-inoculated plants had an enhanced relative water content, plant height, water-soluble carbohydrate and proline contents and antioxidant enzyme activities, but a decreased malondialdehyde content. B₁ exhibited greater effects on most of the traits investigated under the field conditions rather than those with moderate and severe drought stress, while application of the triple bacteria in pots had greater effects on relative water content, carbohydrate and proline contents as well as malondialdehyde. The significant differences in abiotic stress indicators in PGPR-treated plants suggest that these bacteria could be used as biofertilizers to assist plant growth and to reduce the adverse effects of deficit irrigation.     

非充分灌溉及其生理基础

介绍了非充分灌溉的概念及内涵,主要阐述了在非充分灌溉条件下,作物体内产生的适应性生理反应,经非充分灌溉及轻度干旱处理,作物气孔阻力增加,蒸腾失水减少,作物水分散失对气孔开度的依赖性大于光合对其的依赖性。可通过气孔调节作物光合与水分的关系,最终提高作物的水分利用效率;有限度的水分亏缺,有利于同化物向籽粒调运,利用^14CO2标记研究表明,生长后期水分亏缺下,小麦体内存在对花前营养器官“临时库”同化物的再动员和对产量的补偿机制;适度水分亏缺促进了小麦等作物初生根的生长发育,增加深层土壤中的根系与根系活性,防止后期根系早衰。总之,在非充分灌溉条件下,作物能够在营养生长,物质运输和产量形成等方面产生有效的补偿机制,可作为非充分灌溉的重要理论基础。     

Membrane digestion and transport under physiological conditions: a review of available data

A technique to study membrane digestion and transport in the small intestine under physiological conditions has been developed. The technique is based on a continuous perfusion of a chronically isolated loop of the rat small intestine. Membrane hydrolysis and transport of some nutrients in the rat small intestine in chronic, as well as in acute (in situ) experiments was investigated. The absorption of hexoses and amino acids has been found to be 2.5-4 times higher under physiological conditions than in acute in situ experiments. Both the active transport of glucose released from maltose hydrolysis and the hydrolysis of the latter is increased under physiological conditions. A coupling between the final stages of hydrolysis and the initial stages of transport in chronic experiments was shown to be highly efficient; practically all or nearly all glucose released is being transported without entering the luminal phase. The hydrolysis rate of starch during the perfusion of a small intestinal segment in chronic experiments is many times higher than that in acute experiments or under anaesthesia. The enzymatic and transport activities revealed using a widely accepted technique in situ, the more so, in vitro account for only a small fraction of those which are typical of undisturbed processes under conditions close to the physiological. The levels of functioning of the digestive-transport systems of the small intestine considered as natural levels developed in the process of evolution, actually reflect only residual processes and, in most cases, they account for 1/3 to 1/10 of the true level of an actual physiological process.     

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     

Plant ion channels: from molecular structures to physiological functions

Progress in identification of plant ion channels and development of electrophysiological analyses in heterologous expression systems and in planta, in combination with reverse genetic approaches, are providing the possibility of associating molecular entities with physiological functions. Recently, the first attempts to determine in vivo functions using knockout mutants demonstrated the roles of root ion channels. The search for proteins interacting with such channels leads to an even more complex view of the concerted action in protein networks.     

喷灌条件下耕作方式和亏缺灌溉对麦后移栽棉产量和水分利用的影响

探明耕作方式和亏缺灌溉对麦后移栽棉产量和水分利用的效应,对于建立麦后移栽棉的适宜耕作方式及灌溉制度十分重要.在大田条件下设置了翻耕和免耕2种耕作方式(灌水定额均为45 mm)及相应减小50％灌水定额的亏缺灌溉,分析了不同耕作方式和亏缺灌溉对棉花耗水规律、籽棉产量、水分利用效率和纤维品质的影响.结果表明:与翻耕相比,免耕减少了棉田20.3％的棵间土壤蒸发;不论何种耕作方式,亏缺灌溉在不影响棉花产量和纤维品质的同时,有效降低了耗水量,提高了水分利用效率.在喷灌条件下,灌水定额为22.5 mm的免耕耕作方式,不仅可有效降低麦后移栽棉田间无效棵间土壤蒸发,还可实现节水、优质、高产的有效统一.     

Physiological mechanisms contributing to the increased water-use efficiency in winter wheat under deficit irrigation

Deficit irrigation in winter wheat has been practiced in the areas with limited irrigation water resources. The objectives of this study were to (i) understand the physiological basis for determinations of grain yield and water-use efficiency in grain yield (WUE) under deficit irrigation; and (ii) investigate the effect of deficit irrigation on dry matter accumulation and remobilization of pre-anthesis carbon reserves during grain filling. A field experiment was conducted in the Southern High Plains of the USA and winter wheat (cv. TAM 202) was grown on Pullman clay loam soil (fine mixed thermic Torretic Paleustoll). Treatments consisted of rain-fed, deficit irrigation from jointing to the middle of grain filling, and full irrigation. The physiological measurements included leaf water potential, net photosynthetic rate (Pn), stomatal conductance (Gs), and leaf area index. The rain-fed treatment had the lowest seasonal evapotranspiration (ET), biomass, grain yield, harvest index (HI) and WUE as a result of moderate to severe water stress from jointing to grain filling. Irrigation application increased seasonal ET, and ET increased as irrigation frequency increased. The seasonal ET increased 20% in one-irrigation treatments between jointing and anthesis, 32-46% in two-irrigation treatments, and 67% in three- and full irrigation treatments. Plant biomass, grain yield, HI and WUE increased as the result of increased ET. The increased yield under irrigation was mainly contributed by the increased number of spikes, and seeds per square meter and per spike. Among the irrigation treatments, grain yield increased significantly but the WUE increased slightly as irrigation frequency increased. The increased WUE under deficit irrigation was contributed by increased HI. Water stress during grain filling reduced Pn and Gs, and accelerated leaf senescence. However, the water stress during grain filling induced remobilization of pre-anthesis carbon reserves to grains, and the remobilization of pre-anthesis carbon reserves significantly contributed to the increased grain yield and HI. The results of this study showed that deficit irrigation between jointing and anthesis significantly increased wheat yield and WUE through increasing both current photosynthesis and the remobilization of pre-anthesis carbon reserves.     

Understanding down-regulation of photosynthesis under water stress: future prospects and searching for physiological tools for irrigation management

Photosynthetic down-regulation and/or inhibition under water stress conditions are determinants for plant growth, survival and yield in drought-prone areas. Current knowledge about the sequence of metabolic events that leads to complete inhibition of photosynthesis under severe water stress is reviewed. An analysis of published data reveals that a key regulatory role for Rubisco in photosynthesis is improbable under water stress conditions. By contrast, the little data available for other Calvin cycle enzymes suggest the possibility of a key regulatory role for some enzymes involved in the regeneration of RuBP. There are insufficient data to determine the role of photophosphorylation. Several important gaps in our knowledge of this field are highlighted. The most important is the remarkable scarcity of data about the regulation/inhibition of photosynthetic enzymes other than Rubisco under water stress. Consequently, new experiments are urgently needed to improve our current understanding of photosynthetic down-regulation under water stress. A second gap is the lack of knowledge of photosynthetic recovery after irrigation of plants which have been subjected to different stages of water stress. This knowledge is necessary in order to match physiological down-regulation by water stress with controlled irrigation programmes.