Study On The Effect Of Continuous Drought Rewater On Winter Wheat And The Compensation Threshold For Rewater

In recent years,climate variability caused by greenhouse effect has led to frequen t extreme climate events such as persistent drought in the North China Plain.Drought has become one of the main reasons for winter wheat yield reduction in this area.In addition,the impact of drought on winter wheat yield not only depends on the degree of drought,but also on the period of drought onset.Therefore,starting from different growth stages,exploring the effects of continuous drought stress and rehydration on t he growth physiology and yield of winter wheat,clarifying the drought tolerance and rewater compensation threshold of winter wheat,is of great significance for drought re sistance,water-saving cultivation,and stable yield of winter wheat in North China.Thi s experiment takes winter wheat as the research object,and sets different degrees of d rought treatment in three main growth stages,namely the jointing stage(B),heading s tage(C),and filling stage(G),which are normal(CK),light drought(1),moderate dr ought(2),and heavy drought(3),with soil moisture content set(θ)corresponding to field water holding capacity(FC):70%FC<θ≤80%FC、60%FC<θ≤70%FC、50%FC<θ≤60%FC、40%FC<θ≤50%FC,fully irrigated at other stages of growth.Water control was carried out through bucket planting under a mobile rainproof shed.A total of 15 trea tments were set up,including 6 single-stage droughts,5 two-stage continuous droughts(3 jointing-heading stages and 2 heading-filling stages),3 three-stage continuous drou ghts,and 1 control.Study the effects of continuous drought and rewater on the growt h,physiological indicators,yield,and water use efficiency of winter wheat,as well as the compensation threshold for rewater.The main results are as follows:(1)Compared with CK,plant height,leaf area,and dry matter accumulation all decreased under various drought treatments,with a reduction range of 0.9%～23.6%,9.1%～28.7%,and5.8%～39.4%,respectively.This was directly proportional to the degree and duration of drought,and significantly decreased under continuous heavy drought treatment(p<0.05).The compensation effect of plant height appeared on the second day of rewater under single stage drought treatment,and on the fifth day of rewater under multi stage continuous drought treatment;The leaf area and dry matter accumulation under various drought treatments showed compensatory effects on the second day of rewater.(2)Compared with CK,the SPAD will decrease under various drought treatments,with a decrease range of 0.7%～15.6%,which is directly proportional to the duration of drought,but is not a simple positive correlation with the degree of drought.The SPAD during the filling stage,heading filling stage,and jointing heading filling stage were higher in the severe drought treatment than in the moderate drought treatment.After rewater,the SPAD under single stage drought treatment all showed compensatory effects on the second day of rewater,while only continuous light drought rewater had compensatory effects in all treatments.The compensation effect of rewater at each stage is as follows:jointing stage>heading stage>jointing-heading stage>heading-filling stage>jointing-heading-filling stage>filling stage.(3)All three drought levels resulted in a decrease in the fluorescence parameters F_v/F_m,Y(II),and q P of winter wheat flag leaves,while an increase in NPQ.The magnitude of the changes was proportional to the degree and duration of drought.F_v/F_m,Y(II),and q P were1.2%～8.1%,2.2%～25.3%,and 2.7%～17.6%lower than CK under each drought treatment,respectively.NPQ was 2.7%～22.9%higher than CK under each drought treatment,and all fluorescence parameters were significantly reduced compared to CK under continuous moderate and severe drought treatments(p<0.05).After rewater,F_v/F_m,Y(II),q P,and NPQ all showed significant compensatory effects under light drought treatment,returning to the control level.(4)Compared with CK,each drought treatment can lead to a reduction in winter wheat yield,and the degree of reduction increases with the severity of drought.The four components of yield showed varying trends with different drought treatments,but they were all lower than those of CK treatment.Moreover,under the three-stage continuous drought treatments,they continued to decrease with the intensification of drought severity.(5)Compared with CK,the total starch content,amylose content,and branched starch content of grains under various drought treatments decreased,while the ratio of amylose to branched starch increased.The protein content of grains increased with the severity of drought during the filling and heading filling stages,while decreased under other drought treatments.The impact of drought stress on various grain quality indicators of winter wheat is as follows:severe drought>moderate drought>light drought.(6)Compared with CK,the WUE of winter wheat treated with C2,C3,G2,B1C1,B2C2,and C2G2 increased by 4.1%,2.4%,3.9%,1.4%,1.6%,and 6.2%,respectively.However,moderate and severe drought during the jointing stage,as well as three stages of continuous drought,can lead to a decrease in WUE of winter wheat.Drought can reduce the water consumption of plants,and the longer the duration of drought,the lower the water consumption.When water resources are scarce,moderate drought during the filling period(50%FC～60%FC]and continuous moderate drought during the heading filling period(50%FC～60%FC]are reasonable choices for water-saving and ensuring food production.(7)When the soil moisture content is below(60%～70%FC],all indicators of winter wheat are significantly affected.The threshold for significant compensation effects on various growth indicators during the jointing stage is(50%～60%FC],and the SPAD and fluorescence parameters are(40%～50%FC].The threshold for significant compensation effects on plant height,leaf area,SPAD,and fluorescence parameters during the heading stage is(40%～50%FC],and within this threshold range or above,water use efficiency can be improved.The threshold for significant compensation effect of SPAD during the filling period is(50%～60%FC],and the fluorescence parameters are(40%～50%FC];the yield reduction during the filling period is not significant above(50%～60%FC],and water use efficiency can be improved within this threshold range.The threshold for significant compensation effect of leaf area,dry matter accumulation,SPAD,and fluorescence parameters during the jointing heading period is(60%～70FC],and the plant height is(40%～50%FC];the water use efficiency can be improved during the jointing heading stage above(50%～60%FC].The threshold for significant compensation effect on dry matter accumulation during the heading filling stage is(50%～60%FC],and the water use efficiency is highest within this threshold range.The threshold for significant compensation effect on plant height during the jointing-heading-filling stage is(60%～70%FC],with dry matter accumulation,SPAD,and various fluorescence parameters being(60%～70FC].