Study On The Response Of Winter Wheat To Pre-anthesis Drought And Rewatering

Due to the global climate change,the intensity,frequency and scope of influence of agricultural drought disasters are increasing.In China,the annual grain production is reduced by 100~15 billion kg,due to drought and the quality of agricultural products is reduced,which is a direct threat to the national food security.Therefore,to explore how crops respond to the changes of drought environment,and improve the resistance to drought stress and adaptability to drought environment are the key scientific problems to be solved urgently.Zhoumai 22 was selected as the research object to study the effects of different degrees of drought and rewatering at jointing and heading stage on its growth index,physiological index,yield and water productivity,to explore the intensity of crop drought resistance,and to analyze the compensation effect of crop rewatering.It is expected to provide theoretical and technical support for drought resistance and stable yield of winter wheat and determination of efficient irrigation system.The main results of the experiment are as follows:(1)The root system of winter wheat suffers from drought at jointing stage,which will increase the root diameter and decrease the number of root hairs,total root length,root surface area and other indexes,resulting in the decrease of root dry weight.After short-term drought and rewatering,the root system can produce compensation effect and recover to some extent.The effect of drought on root system was greater at jointing stage than at heading stage,but the compensation and recovery ability of root system after rewatering was also higher than that at heading stage.With the increase of drought degree and time,the root system extends downward and grows,so that the distribution proportion of each root index in the lower layer increases,but the total absolute amount of root system will decrease obviously.(2)With the increase of stress degree and stress time,the inhibition of plant height and leaf area increased,in which jointing stage had a greater effect on plant height,heading stage had a greater effect on leaf area,and the compensation effect of plant height and leaf area after drought and rewatering was heading stage > jointing stage > continuous treatment.Although there was compensation effect after rewatering,it could not completely counteract the effect of drought.Leaf area is more sensitive to drought than plant height.(3)Drought led to the decrease of SPAD value,and the effect of drought on SPAD value at jointing stage was greater than that at heading stage,and the compensation effect was higher after rewatering.The leaf water potential was positively correlated with soil moisture,and the leaf water potential decreased with the decrease of soil moisture.The effect of drought on leaf water potential was jointing stage > continuous drought > heading stage.The recovery ability after rewatering was jointing stage > heading stage > continuous drought.The transpiration rate is stronger after drought and rewatering at heading stage.(4)The changing trends of net photosynthetic rate,stomatal conductance and leaf WUE were consistent,they were decreased significantly with the increase of drought degree and drought duration in the same growth period.The effect of drought on growth period was as follows: jointing stage > heading stage > jointing stage.The drought degree of non-stomatal limiting factor under short-term drought is severe drought,and the drought degree of non-stomatal limiting factors under long-term drought are moderate drought and severe drought.The recovery at jointing stage was faster,and the degree of recovery at heading stage was high,so it was finished continuously.(5)Dry matter accumulation decreased gradually with the increase of drought degree,and the effect of drought on dry matter accumulation was jointing stage > heading stage.The amount of dry matter transfer after drought and rewatering at heading stage was generally higher than that at jointing stage,and it was higher in middle drought treatment.Continuous light drought and continuous moderate drought caused adaptive changes in plants,biomass accumulation was even higher than that in single-stage treatment,and continuous severe drought seriously reduced dry matter accumulation and transport.(6)After single-stage light drought and rewatering,the yield didn’t decreased significantly,but the severe drought at jointing stage promoted the increase of 1000-grain weight,and significantly decreased the number of panicles and grains per spike,resulting in a decrease in yield.Heading stage and continuous drought reduced the number of panicle,grain number per spike and 1000-grain weight at the same time,but the yield reduction was more serious due to the longer duration of continuous drought stress.The jointing stage had a greater effect on the number of panicles and grains per ear,and the heading stage had a greater effect on 1000-grain weight.Finally,after drought and rewatering,the yield was as follows: heading stage > jointing stage > jointing and heading continuous.After light drought and moderate drought and rewatering,the water use efficiency of winter wheat increased obviously,and the response of water consumption to drought was heading stage > jointing stage > continuous drought,and decreased with the aggravation of drought.In single-stage drought,the greater the degree of drought,the lower the water use efficiency of wheat;under the condition of light drought and rewatering,the water use efficiency of wheat was the highest at jointing stage,and the continuous jointing and heading was the highest under the condition of moderate drought and rewatering.Under the condition of heavy drought and rewatering,the water use efficiency at heading stage was the highest.(7)when the soil moisture content of wheat is below 70%,the growth,physiology and production function of wheat are seriously affected.Among them,the root system,leaf area,SPAD,leaf water potential,photosynthetic characteristics and other indexes at jointing stage can obviously recover 40%,and the plant height recovery threshold is 50%.When the relative water content of soil is more than 60% at jointing stage,the yield reduction is not significant,and more than 50% can significantly improve water use efficiency.The obvious recovery threshold of root system,plant height,leaf area and photosynthetic characteristics at heading stage was 40% and 50%.At heading stage,the yield reduction is not significant when the soil relative water content is above 60%,but the water use efficiency can be improved when the soil relative water content is more than 40%.Continuous drought seriously reduces the yield,and other indexes can not be recovered after rewatering,so continuous drought should be avoided.If wheat needs to control water before flowering,it is best to control the level of light drought at heading stage to ensure adequate water supply at jointing stage.