Highly efficient use of limited water in wheat production of semiarid area

PROGRESS IN NATURAL SCIENCEVol. 13 ,No.12 ,December 2003REVIEW ARTICL .EHighly efficient use of limited water inwheat production of semiarid area'DENG Xiping1** , SHAN Lun2 , INANAGA Shinobu3 and Mohanmed Elfatih K. ALI4(1. State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau , Institute of Soil and W ater Conservation , ChineseAcademy of Sciences , Shaanxi 712100 , China ;2. Northwest Sci- Tech U niversity of Agriculture and Forestry , Shaanxi 712100 , China ;3. Arid Land Research Center , Tottori University , Hamasaka 1390 , Tottori 680 , Japan ;4. EI-Obeid Research Station , Agricultural Re-search Corporation ,P. O. Box 429 , EI-Obeid , Sudan )Received April 11 ,2003 ; revised June 3 , 2003.AbstractTo obtain a greater yield per unit rainfal is one of the most important challenges in dryland w heat production. Highlysociated with w ater deficit and variable conditions. In addition , it reveals the compensatory efect of limnited irrigation and fertilizer supple-ment on wheat water-use efcency( W U E ) and highlights the breeding of new varieties for high W UE that could improve w heat produc-tivity under w ater-limited environments in the semiarid area. Considerable potential for further improvement in wheat productivity in semi-arid area seems to depend on effective conservation of moisture and efficient use of this limited w ater. Different crops , soil and w ater man-agement strategies should be adjusted according to the conditions that prevail in the various semiarid areas. By combining soil and waterconservation approaches with regulating the cropping system by culivating drought-tolerant and water-saving cultivars , the increase inw heat productivity could be achieved.Keywords : semiarid area , dryland wheat , physiological adaptation , WUE improvement.Global demand for wheat is growing faster thanbution and intensity41. Wheat response to this watergains realized in genetic yield potential. Currently thedeficit and variable environments is complex andgain increase is less than 1 % per year in most re-uninsurable , because such conditions can cover differ-gions. To improve total production in China , at-ent situations including variable frequency of droughttention has been focused on expansion in areas withand wet periods ; variable degrees of drought ; speedlow and medium yields in the semiarid area. This hasof onset of drought conditions ; and varying patternsrequired the development and dissemination of W heatof soil water deficit and/ or atmospheric water deficit.production technologies that lead to sustainable andGreat yield potential of w heat production instable wheat yields in these areas 21semiarid area existed ; to improve wheat yield , how-Periods of drought alternating with short periodsever，biggest challenge is effective conservation andof available water are conditions common to manyefficient use of limited w ater resources. The objectivesemiarid areas of the world31. The typical semiaridof this paper is to view some benefit effects of w heatarea in China , for instance , characterized by w aterresponse to water deficit and variable conditions , disshortage and low productivity ，has special naturalcuss w heat water use efficiency( W UE ) improvementconditions and ecological environment. Annual pre-and exploit drought- tolerant and water-saving poten-cipitation in the area is about 350 ~ 550 mm and thetial of w heat for high efficient use of limited water re-percentages of its distribution in the spring , summer ,ourd中国煤化工"-ina.autumn and winter are 12% ~ 15% ,46% ~ 65% ,1TYHCNMH G water deficit and20% ~ 35% and 1% ~ 3% , respectively. Rainfall ,invariable conditionsthe form of storms , occurs mainly in the period fromJuly to September , characterized by irregular distri-W heat drought tolerance is multi-routes , with all* Spprtyt 片数搓jior State Basie Reserh Development Program of China( 199901708 )** To whom cortp品dence should be ddressed. E-mail : dengxp@ ms. iswe. ac. cn882Progress in Natural Science Vol.13 No. 122003the mechanisms involved not clearly understood. Re-U nder such conditions , the ability of seedling to up-cent researches on the effects of water deficits ontake water is increased and slow seedling growth isphysiological processes at the molecular level showmaintained during w ater deficit.that some enzy matically mediated processes increaseFrom an agronomic viewpoint , Whanet al.[27] ,but others decrease 51. Root/ shoot communication isfor example , suggested that indeterminate cultivarsbeing increasingly studied at the molecular levelA crop' s sensitivity to drought varies during differentthat have early and vigorous seedling establishmentstages of its life cycle. This provides the possibility to .accumulated a relatively large amount of biomass bychoose the crucial moments for watering the crop tothe beginning of the seed flling stage , and thus werereduce drought stress 10，Also a crop' s response toable to remobilize accumulated photosynthate in re-drought stress and the degree to which yield is re-sponse to declining soil moisture. Such cultivars wereduced vary across the different growth stages of thebest adapted to drought conditions. Water stress in-crop , especially those closely related to yield forma-hibited plumule elongation and reduced seedling vig-tion. The order in w hich w heat physiological process-or , resulting in shorter coleoptiles ，w hich leads toes are serially affected by drought seems to bepoor establishment and a reduced yield. To achievegrowth , stomatal movement , transpiration , photo-better establishment and high yields under the water-synthesis and translocatiort 11-131. These observationslimited conditions , longer coleoptile length probablypermit irrigation scheduling to be designed so as tois one of the approaches to this goal. Thus , longcoleoptile w heat plants or lines can be further testedminimize loss in wheat yield.to select the desired seedling establishment. TH1.1 W heat drought- tolerance during seedling estab-availability of molecular markers for some coleoptilelishmentlength genes in wheat can further enhance selectionefficiency. High throughput markers are being devel-Wheat seedling establishment under water deficitoped for genes of interest and efficiency of implemen-conditions has been widely studied 1415] and howtation of these markers assessed and optimized in Aus-seedlings respond to stress signals and how stresstralian CSIRO w heat breeding progrant 31affects regulation of gene expression have resulted inan understanding of these processes at the molecular1.2 WUE and root-shoot relations of wheatlevef 16.17].. In particular , major results on hydrolysisWhile the current interest in research at thein seed germinatiort 18↓, anabolism during seedling es-tablishment，plumule elongation grow tt|「20], pro-molecular level is important , it should accompany research on water relations at the whole plant level.teins and genes regulated by plant hormones 21, aswell as water absorption mechanism during seedlingThe success of the w heat plant in producing yield de-establishment under water deficit conditions have alpends primarily on the success of leaves in controllingbeen reported2231.water loss and the effectiveness of roots in taking upwater when the soil water is limited. Tolerance of de-It is generally accepted that crops are often lesshydration depends on characteristics at the moleculartolerant to drought during germination and seedlinglevel，such as osmotic adjustment ，the water trans-stages24251. Deng et al.!121 showed that of all theduction in tissues , and the manner in w hich w aterstages of active axis extension ，germination , plumuledeficit affects enzy me- mediated processes. Clearly ,elongation and emergence of spring w heat，theboth avoidance and tolerance of water deficit will con-plumule elongation stage is the most sensitive one totribute to successful w heat production under semiaridwater deficit. Therefore , under water deficit condi-conditions. Avoidance of severe w ater deficit requirestions , the maintenance of anabolism and slow growthcoordination at the W hole plant level bet w een the con-are greatly associated with ATP energy level in cells ,trolpiring shoots and wateras seedling establishment involves the_ energy-requir-absc中国煤化工ms With the methodsing metabolic reactions. Deng et al.L26 J suggested thatfg:YHC NM H Gle isotope , Zhang andthe mechanism of seedling drought tolerance seems toShart 281 demonstrated that sequence of WUE in mod-involve regulating ATP energy level to change the ra-ern w heat cultivars is irrigated varieties > varieties oftio of catabolism to anabolism in such a way that re-both irrigated and dry land > dry land varieties.sults in the_ accumulation of osmotic component andZhang et al.! 291 showed that in w heat evolution fromdepression 6f好otic potential in growing tissue.2n→6n , WUE at whole plant level increases withProgress in Natural ScienceVol.13 No.12 2003883 .the increase of ploidy chromosomes , root system sizeder gradual soil drying conditions , wheat exhibits aand root/shoot ratio of wheat decrease with the in-higher photosynthetic rate( Pn ) than under fast soilcrease of ploidy chromosomes under drought and irri-drying conditions. In the former，osmotic adjustmentgated conditions. Root system growth has an adverseincreases to a certain extent while in the latter processredundancy for WUE , and the root redundancy re-it remains constant. Osmotic adjustment allows forduces with the increase of ploidy chromosomes ,maintenance of photosynthesis and growth by stom-which results in the increase of wheat WUE at w holeatal adjustment and photosy nthetic adjustment 36237].plant level. These results suggested that the use ofThe reported evidence showed that under mild and/orgenetic breeding to excavate w ater-saving potential ofmoderate soil w ater deficit conditions , photosyntheticwheat is possible.depression w as caused by stomatal closure or stomatallimitation , but not by biochemical reactions. Howev-A deep root system is sy nonomous with more，under severe soil water deficit conditions，non-water uptake from the soil and better performancestomatal factors including some limiting enzy mesunder drought. It may be，however，that the rootcould have been responsible for the decline in photo-systems of cultivars grown in a given region are al-synthetic capacity 38-40]. M idday declines in photo-ready adequate and further improvement may not besynthesis were mainly induced by severe vapor pres-required. Information on w hether current cultivarssure deficit , and stomatal limitation was suggested asabsorb all the available soil water is required to estab-a major cause 41 421. U nder natural semiarid condi-lish this 30]. If soil water remains after harvest then ations , however , this decline usually resulted from soilgenetic improvement in rooting depth and/ or distri-water deficit that induced a decrease in leaf water pcbution may be required. This trait is , of course , dif-tential at midday. Deng et al.! 131 reported that bothficult to measure. The simplest way to increase root-soil water deficit and high vapor pressure deficiting depth and root distribution of crops is to increasethe duration of the vegetative period( i.e. the periodsimultaneously induced the midday depression in pho-up to anthesis ). This may be achieved by sowing ear-tosynthesis，indicating that both stomatal and non-lier or later flowering genotype if this is feasible.stomatal limitations were responsible for photosyn-Greater osmotic adjustment may also result in morethetic decline in spring w heat in the semiarid environ-root growth and ability to uptake additional soil wa-ment.ter. However ,selection for osmotic adjustment is notU nder water deficit conditions , the crop is ableeasy at the present time ，although a novel method ofto synthesize abscisic acid( ABA )by its root system.selection in the haploid stage in wheat has recentlyABA is then transported through the xylem to leaves.been demonstrated 31].causing regulation of several ion channels in guard1.3 Photosynthetic characteristics of wheat undercells which triggering stomatal closure43441. Thismay be linked to the role of farnesylations that havedrought conditionsbeen connected with ABA signal conductiort 45 A6].U nder drought conditions , stomatal closure andWith regard to chloroplast capacity to fix CO2 ，the .inhibition of chloroplast activity reduce photosynthe-evidence shows that the Rubisco holoenzy me is assem-sis 32]. Stomatal closure increases the resistance tobled in a catalytically inactive form and is activated byCO2 diffusion into the leaf. Inhibition of chloroplastRubisco activase( RCA )47 A8].activity at low soil w ater potential decreases the ca-Deng et al.[49] indicated that the notable middaypacity to fix available CO2 , and this cannot be over-come by increasing the concentration of CO[33]. Al-decline in stomatal conductance that was parallel tothough stomatal closure generally occurs w hen plantsphotosynthetic rate depression resulted from severeare exposed to drought , in some cases photosy nthesisvapmidday. The deviation ofmay be more controlled by the chloroplast capacity toston中国煤化工the control and soilmois:YHCN M H Gis closely related to thefix CO2 than by the increased diffusive resistance 341.However , how photosy nthesis adapts to drought en-leaf water status that was obviously affected by theprevailing soil moisture deficit. The hypothesis was ,vironments is not well understood.therefore，proposed that molecular mechanism ofIn semiarid. environments，photosynthesis isstomatal conductance variation and intercellular CO2variable with持rent soil moisture contents35]. Un-concentration oscillation is closely linked with ABA-884Progress in Natural Science Vol.13 No.12 2003reduced stomatal response and activation status of thedrought from that one at w hich supplemental irriga-enzy me Rubisco affected by circadian oscillation oftion results in the highest yield.RCA.3 Effect of soil fertilization on wheat WUE2 Compensatory effect of limited irrigationDrought and poor soil fertility are the main re-in wheatstrictive factors for the production of dryland wheat inLoomis and Connof 50] suggested that there are .the semiarid and eroded areas of China. Because poorthree strategies available to improve the water use ofsoil fertility results from severe water loss and soilcrops in dry areas. The first is to maximize crop e-erosion，supplying the nutrient needs of the w heatvapotranspiration( ET ). The second is to maximizeplant is essential for increasing grain production in thecrop transpiration( Tr ),as a fraction of total evapo-low yielding areas of semiarid area. This can betranspiration. And the third is to maximize crop .achieved through the use of organic fertilizers , for ex-WUE. Consistent with these strategies and water .ample by applying animal manure , incorporating croplimited conditions , Deng et al .1. [51 ]proposed thatresidues and including legumes in rotatiort 4. Chemi-200 mm of supplemental water is needed to achievecal fertilizers are also used to increase grain productionthe maximum grain yield ; 100 mm of supplementaland fulfill the crop' s nutrient needs. U nder rainfedwater is necessary to get the greatest WUE ; andconditions , application of nitrogen and phosphorous60 mm of supplemental water is indispensable for thefertilizers could considerably improve w heat yields.highest irrigated WUE. In semiarid areas of NorthRainfall variability greatly increases the risk of usingChina , the critical water quantum for limited irriga-fertilizer in dryland environments. However , esti-tion of spring wheat is 60 mm.mates from farmers' fields and ex perimental stationsindicated that the wheat crop usually recovers onlyMany studies 52 53] have looked at the yield losses30% ~ 50% of the nitrogen that farmers appl:associated with drought at different stages of plantThe rest is lost , either dissipated into the atmospheredevelopment. V llareal et al.54J showed that crownor leached down the soil profile or into ground wa-root initiation and anthesis are the two stages attef58].which yield losses from drought stress can be mostcritical to wheat. Current researclhrS5] is aimed at i-The nutrients that are found to be most limitingdentifying different plant traits that would allowin the loess hilly region of China are N and p41.wheat varieties to withstand the different types ofMost of the soils in the loess region of China are cal-drought that occur in the developing world.careous and these soils are particularly distributed onthe eroded hilly tops. The deficiency is really a prob-Liang et al.! 561 demonstrated that the drying-re-lem of runof591. The yield and W UE increase fromwatering alternation had a significant compensatoryadded N were observed in several dryland areas w hereeffect that could reduce transpiration and keep w heatcrops were grown on the same land for severalgrowing and WUE significantly increasing underyears. Liu et al.' 60」indicated that maximum yielddrought conditions. Deng et al.[51] showed that , inand highest WUE were achieved under the optimumthe Guyan County of the Ningxia Hui Autonomousfertilizer input of 90kg N and 135kg P2Os per ha inRegion of China , where the annual precipitation ishe semiarid field conditions of loess hilly area inabout 450 mm and the annual mean temperature isNingxia. Increase in soil fertilization was positively6.5 C ,a single irrigation of 600 m3 /ha applied at thecorrelated with grain yield and WUE in springjointing stage( equivalent to 30% of irrigated volumewheat , with a correlation coefficient of 0. 959 andof water for a full cropping season with the highest0.894，respectively. Increasing fertilizer level signifi-yield) yields up to 75% of the highest yield. Thiscant:1:t number , kernelsamounts to a 2.8 kg increase in grain yield per cubicspik中国煤化工ie sikelet number wWasmeter of water. The optimum time for limited irrita-sens:MYHC N M H Geas kernel number andtion in spring wheat is the jointing stage and the wa-weight was mainly affected by plant density. Fertil-ter deficit critical period and the optimum irrigationization applied in spring w heat improved root systemtime in wheat are not at the same growth stage. Itdevelopment and especially enhanced roots growth inseems essential to make a distinction bet ween the crit-the cultivated soil layer of 0 ~ 20 cm. A melioratedical grow th sngeat which yield is greatly reduced byroot system was able to improve crop water use andProgress in Natural ScienceVol.13 No.12 2003885nutrient absorption and hence , crop yield and WUEderstanding of how WUE can be improved and howwas increased. Their study highlighted the compen-farming systems can be modified to be more efficientsatory effects of improving inorganic nutrition on then water use1l. Maximizing WUE may be morehighly efficient use of limited water in dry land wheatsuitable in areas where water , not land , is the mostproduction .limiting factor621. There is a need for accurately un-derstanding of w heat response to water deficit condi-4 Ecophysiological approaches for wheattions on real-time. Consequently , it is possible toWUE improvementcombine knowledge of crop adaptation and water usewith the available technology to control the efficientTo achieve a greater yield per unit rainfall is oneuse of limited w ater resources .of the most important challenges in dryland w heat .WUE represents a given level of biomass or grainThe effective use of precipitation and optimiza-yield per unit of water used by the crop. With in-tion of WUE are critical for promoting wheat yield increasing concern about the availability of water redryland farming systems 63. These can be summa-sources in both irrigated and dryland agriculture ,rized in Figure 1.there is renewed interest in trying to develop an un-Biological modificationEnvironmental controlRegulate stomata toControl soil and water loss,increase Pn/Irincrease soil moisture storageImprove carbohydrateUse mulch to reduce soiltranslocation for h igh HIsurface evaporationecreasecrop| Improve fieldfield waterWUEuse ratioModify genes for goodImprove root growth to usedrought resistancedeeper soil waterBreed and select for highCollect run off water forWUE genotypesRaise precipitation use efficiencycsupplesupplement irrigation| Realize highly efficient use of limited waterresoureesFig. 1. Comprehensive technical approaches to improving crop production in semiarid regions with eroded environments( HI : harvest index ).The water deficit and variable conditions including prevention of water loss and soil erosion , e-semiarid environments are the major issues influenc-limination of topsoil evaporation , extraction of watering w heat growth. W ater-saving agricultural practicestored in deeper layers and steady heightening of themust , therefore , be designed and utilized. Central toabsorbable share of water by crops must be adopted.such research should be the relationship between theIn the semiarid Loess Plateau , for instance , the wa-effect of drought stress on crop physiological processester-saving drive is to raise the rainfall utilization ratioand the yield formation ability.by the construction of high-yield farmlands throughthe building of leveled terraces , the utilization of har-In the southern hilly area of Ningxia Hui Au-vested rainwater for limited irrigation ，the use oftonomous Region of China , with about 450 mm of an-tilla中国煤化工water and soil, the in-nual precipitation from 1980 to 1994，the springtrodCNMHGVal; varieties and the appli-wheat yield was 0.75~ 2.25 tones/ha ，with averagecatiom ur lrduuc allu 1c1 uucer.MHEspecially , for thewater consumption of 280 mm , which is about 62%low yielding of dryland w heat production ，the w ideof the annual rainfalt 11. The above figure shows thatuse of chemical fertilizer has played a major role inthere is still a considerable potential for further im-this aspect2491. In a 10-year period( 1980 to 1990 ),provement i迎the use of rainfall received. To raisedryland w heat production in this area doubled its an-rainfall uthizam护rate , a comprehensive approach in-886Progress in Natural Science Vol.13 No. 122003nual output. The major contributing factor to themain pathways for high W UE in limited irrigation arechange was the use of chemical fertilizef 4].to increase the output per unit of water( engineeringChanges in soil management practice to reduce e-and agronomic management aspects ) , reduce losses ofvaporation from. the soil surface have been sucessfulwater to unusable sinks ，reduce water degradationin some locatiorf64]. It is possible to increase WUE( environmental aspects ), and reallocate water toby 25% to 40% through soil management practicehigher priority uses ( societal aspeets )70].that involves illage. Li and Xiad 6 ] demonstrated5 Perspectivesthat the use of a mulch crop to cover fields with greenmanure plants , crop residue , or plastic film protect-In the last decade , our understanding of the pro-ing the soil from moisture loss by evaporation, re-cessesunderlying wheat response to drought , at theduces soil erosion and thus , improves soil fertility andmolecular and whole-plant levels, has rapidly pro-conserves water. These changes result in an increasedgressed. Knowledge of these processes is necessary towheat yield and W UE in the low yielding areas exam-improve crop management and breeding techniques.ined. xrt66 J showed that mulching signifcantly im-Hundreds of genes. that are induced under droughtproved water conservation and soil fertility and result-have been identifief 71. A range of tools , from geneed in a large increase in w heat yield in dryland areas.expression patterns to the use of transgenic wheatWhen 30 tones/ha of green manure was used on fal-plants，is being used to study the specific function oflow land ,about 50 mm of water could be conserved，those genes and their roles in w heat plants adaptationsoil organic matter and nutrients simultaneously en-to water deficit and WUE improvement 72]. Howev-hanced , yield increased by 2. 25 tones/ha and WUEer，because wheat responses to drought are cascaded ,increased by 23%. Numerous results in different re-the functions of many of the genes are still unknown.gions agree that straw mulching significantly im-The new tools that operate at molecular , w hole-plantproves the field ability of natural rainfall restoringand ecosystem levels are revolutionizing our under-soil water supplying ，and soil evaporation restrict-standing of w heat plant response to drought , and ouring6-69 . To recognize the water and fertility short-ability to monitor it. For example , carbon isotopeage in semiarid areas, these measures of strawdiscrimination(△"C)is a measure of the 13C/2C ra-mulching are important to economize the limited wa-tio in plant material relative to the value the same ra-ter resources ,as well as avoid over uptake of soil nu-tio in the air on which wheat plants fed. The△I3C istrients. It should be emphasized that straw mulchingpositively related to the ratio of the intercellular CO2makes no change of crop gross water consumption a-concentration and the atmospheric CO2 concentration.gainst control one , but it changes the portion bet weenTherefore s 13C correlates with WUE of wheat. Con-soil evaporation and plant transpiration. This meanssequently ,△"C ,due to its convenience and a rela-that straw mulching improved use efficiency of limit-tively low cost ，has become a useful indicator of dif-ed water resources , and in turn improved wheat pro-ferences in WUE. Recently this method has beenductivity .used for high WUE breeding in wheat73]. Othertechniques such as genome- w ide tools and thermal orGenetic advances in grain yield under rainfedfluorescence imaging may allow the genotype-pheno-conditions have been achieved by empirical breedingtype gap to be bridged , which is essential for fastermethods. Progress is slowed , however , by the inter-progress in high W U E research.action bet ween a large genotype and season , and loca-tion arising from unpredictable rainfalls, which is aA possible means of realizing high WUE offeature of drought environments. A good understand-wheat in semiarid area is to manage transpiration soing of factors limiting and/or regulating yield nowthat relatively more water is used , since highly effi-provides us with an opportunity to identifty and thenclent中国煤化Ietermined by both cropselect for physiological and morphological traits thatwatease in transpiration ef-increase the efficiency of water use and yield underficiTYHCNMHGanincreaseinPnanda.rainfed conditions3].decrease in stomatal conductance .Wheat underdrought stress has self-regulatory processes for endur-WUE is broader in scope than most agronomicing the adversity . These range from metabolic adap-applications. and, must be considered on a watershed ,tation to reduced growth. If the drought does notbasin, irfhga8listrict , or catchment scale. 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