Study On The Response Of Winter Wheat To Continuous Drought

With the continuous northward movement of the main grain producing areas in China and the impact of global climate change,the frequency,intensity and impact scope of agricultural drought disasters are increasing and expanding,which directly threatened the national food security.In order to study the effects of different levels and different stages of continuous drought on the growth and development of winter wheat,and to improve the adaptability and resistance of winter wheat to complex drought stress,the experiment adopted the method of pot-planted,taking"Zhoumai 22"as the test variety,and designed different levels of drought stress treatments at the main growth stages of Winter Wheat(Jointing stage B,Heading stage C,Filling stage G)design different levels of drought stress treatments(Light drought:60%?70%FC,Moderate drought:50%?60%FC,Severe drought:40%?50%FC,the FC stand for field capacity)and the number of stages of different continuous drought(two-stage continuous drought and three-stage continuous drought).There were 19 treatments including 9 treatments of single-stage drought,6 treatments of two-stage continuous drought,3 treatments of three-stage continuous drought,and 1 control treatment.The effects of continuous drought at different growth stages and different levels on growth,physiological indexes,yield and water use efficiency(WUE)were investigated.The main results are as follows:(1)All three levels of drought stress significantly reduced the leaf area of winter wheat,but the plant height did not necessarily decrease.The decrease of leaf area ranged from 20.6%to 81.8%,and the variation of plant height ranged from 29.9%to101.7%.With the aggravation of stress and the extension of stress time,the decrease of plant height and leaf area would increase.The effect of continuous drought on plant height and leaf area was not simply decreased with the increase of stress time.Under the same drought conditions,the sensitivity of plant height to water deficit at each stage was as follows:B-C continuous drought>three-stage continuous drought>jointing stage>C-G continuous drought>heading stage>filling stage;The order of sensitivity of leaf area to water deficit at each stage was as follows:C-G continuous drought>three-stage continuous drought>filling stage>B-C continuous drought>heading stage>jointing stage.In order to ensure plant height,moderate drought,severe drought or continuous drought should be avoided at the jointing stage;in order to ensure the leaf area,filling stage drought or continuous drought should be avoided.(2)Drought at different stages of winter wheat led to the decrease of root tip number,total root length,root surface area and other indexes,and then resulted in the decrease of root dry weight.In order to promote root growth,moderate drought or severe drought stress can be accepted at jointing stage,but multi-stage continuous drought should be avoided.Under normal treatment,root distribution of winter wheat decreased with soil depth increasing.The root distribution of jointing stage drought,heading stage drought and two-stage continuous drought treatment was similar to that of CK,and the proportion of deep root increased to 42.39%,41.05%,41.79%and 46.21%on average with the increase of drought and stress time,respectively.On the contrary,the proportion of shallow roots in filling stage drought and three-stage continuous drought increased to 60.36%and 67.02%,respectively.(3)The SPAD value of flag leaves decreased under all three levels of drought stress.The SPAD value did not decrease continuously during the filling stage and the thresholds of soil moisture rebounding and rising were 60%and 50%,respectively.The sensitivity of SPAD value to drought at different growth stages can be ranked as follows:heading stage>B-C continuous drought>three-stage continuous drought>jointing stage>C-G continuous drought>filling stage.(4)There was a positive correlation between leaf water potential and soil moisture.The more soil water decreased,the greater leaf water potential decreased,and the decrease range of leaf water potential was 6.0%?261.8%.The order of sensitivity of leaf water potential to drought at different growth stages can be ranked as follows:filling stage>C-G continuous drought>three-stage continuous drought>jointing stage>heading stage>B-C continuous drought.(5)All three levels of drought stress can lead to the decrease of net photosynthetic rate,stomatal conductance and transpiration rate of winter wheat.The variation of intercellular CO₂ concentration was more complex and exceeded that of the control treatment when soil moisture dropped to 50%.The sensitivity of photosynthetic parameters at different stages to drought was sorted as P_n:heading stage>filling stage>C-G continuous drought>three-stage continuous drought>B-C continuous drought>jointing stage;G_s:filling stage>C-G continuous drought>three-stage continuous drought>heading stage>B-C continuous drought>jointing stage;T_r:filling stage>three-stage continuous drought>C-G continuous drought>jointing stage>heading stage>B-C continuous drought.The threshold value of soil moisture producing non-stomatal limiting factors was 50%under single-stage drought condition,and 60%under multi-stage continuous drought condition.The threshold of non-stomatal limiting factors in winter wheat would advance with the increase of drought duration.(6)All the three levels of drought stress resulted in the yield of winter wheat,but did not necessarily reduce water use efficiency.The yield of all treatments decreased with the increase of drought and drought duration.However,under severe drought conditions,the yield of three-stage continuous drought was higher than that of B-C continuous severe drought.Among the three factors of yield factor,the variation trend of effective panicle was consistent with yield,while the variation trend of grain number per panicle and thousand-grain weight was not completely identical with yield.The jointing stage is the most sensitive stage of yield to water deficit.Under the condition of this experiment,when the total water consumption reached 411mm,the winter wheat yield reached the maximum.The order of the effect of drought on yield decline in different growth stages was as follows:B-C continuous drought>three-stage continuous drought>C-G continuous drought>jointing stage>filling stage>heading stage.Under single-stage drought and three-stage continuous drought conditions,WUE decreased with the increase of drought levels.However,under the two-stage continuous drought condition,the WUE of moderate drought treatment was the highest.Among all the WUE treatments,the light drought was the highest at the filling stage and the B-C continuous severe drought was the lowest.Excessive water consumption does not increase winter wheat yield,but decreases WUE.The threshold value of soil moisture from jointing stage to grain filling stage ranged from 64.2%to 78.8%,and the threshold value at heading stage was the lowest.Therefore,in order to solve the contradiction between supply and demand in water shortage areas,from the perspective of water saving and high efficiency,it is acceptable to accept moderate drought in a single stage(60%-70%FC),but it is necessary to avoid severe drought as much as possible,especially multi-stage continuous severe drought.