Influence Of Drought Stress At Flowering Stage On Photosynthetic Characteristics And Yield Of Soybean

Global climate change makes drought a major disaster in the world,and is one of the main factors that affect crop yield.Drought in Anhui province is most typical of drought in summer with long duration and great influence.At this time,soybean in Anhui is in the stage of flowering and pod,it is the most sensitive to the change of water deficit.Once the drought disaster occurs,it will directly affect the yield and plant morphology of soybean.Therefore,it is very important to improve the yield of soybean,improve the quality of soybean and develop the drought and drought resistance by simulating drought in the podding period of summer soybean and studying the changes of photosynthetic characteristics,agronomic characters and yield.In this paper,four different intensities of drought,CK,LD,MD and HD,were set up according to the local meteorological data and the data of soybean growing period.Simulated drought treatments were conducted at flowering and podding stage of soybean,and photosynthetic characteristics,agronomic traits and yield indices were measured at flowering and podding stage.In order to reveal the effects of simulated drought on photosynthetic characteristics,agronomic traits and yield of soybean,the correlation analysis of each variable was carried out to provide reference for scientific and rational irrigation and water utilization.The main conclusions are as follows:(1)With the increase of drought severity,the daily net photosynthetic rate of summer soybean leaves was inhibited to varying degrees.The effect of drought on the net photosynthetic rate of soybean leaves at the grain-filling stage was greater than that of the late flowering stage.Compared with CK,the daily average net photosynthetic rate of LD,MD and HD decreased by 7.00%,20.61%,and 31.31%,respectively,and the grain size decreased by 11.43%,25.61%,and 45.71%,respectively.Among them,HD and CK were in the drum.The granular period reached a very significant level of difference.Photosynthetic noon depression is more evident at noon time under drought conditions.(2)The daily mean value of transpiration rate of summer soybean leaves decreased with the increase of drought intensity,and the daily change curve showed a trend of increase and then decrease.Compared with CK treatment,the daily average transpiration rate of LD,MD,and HD decreased 6.53%,9.94%,and 18.70%,respectively,and the grain size decreased by 21.09%,33.13%,and 41.88%,respectively,of which HD treatment and CK ratio The difference is extremely significant.(3)The daily average stomatal conductance of soybean increased with the degree ofdrought,showing a decreasing trend.Compared with CK,LD,MD,and HD were decreased by 6.47%,15.12%,and 18.83% during the flowering stage.Compared with CK,the LD,MD,and HD levels did not reach significant levels.It decreased by 6.41%,17.37%,and 21.38% respectively,and the levels of MD,HD and CK reached significant difference.(4)The daily change curve of summer soybean water use efficiency index first decreased and then increased,and the daily average value showed a trend of decreasing with increasing drought intensity.In flowering stage,compared with CK treatment,LD increased by 1.75%,MD,HD decreased by 7.54%,13.02%,showing LD> CK> MD> HD,but the differences between the treatments were not significant;During the period,compared with CK treatment,LD,MD increased by 12.45%,11.46%,and HD decreased by 3.53%.The water use efficiency of leaves under LD and MD treatment was slightly higher than that of CK.(5)The daily average value of light energy utilization rate of soybean leaves gradually decreased with the increase of drought intensity.The average daily light energy utilization rate of soybeans during the grain filling period decreased as compared with the flowering period.Compared with CK treatment,LD,MD,and HD decreased 8.34%,35.81%,and42.90% in the flowering stage,and decreased 12.26%,42.91%,and 46.49%,respectively,in the grain filling stage.Compared with CK,MD,HD and CK all passed the test of significant difference.The daily average reduction of MD and HD was significantly greater than that of flowering stage at the grain-granule stage.When the drought reached MD level,the utilization rate of light energy was obviously suppressed.(6)Drought had a certain effect on the morphological indexes of soybean plants.With the increase of drought degree,plant height,leaf area,number of branches,number of leaves,stem diameter,number of main stems,height of bottom pods,etc.There is a downward trend.In the indexes of plant height,leaf area,number of branches,and number of stem sections of soybean,the differences between HD and CK reached significant levels,and drought had the most significant effect on HD level.There was no significant difference among the treatments in the height of bottom rake,stem diameter and number of leaves.(7)The number of rhizobia caused by drought decreased,and LD,MD,HD were decreased by 5.51%,20.47%,and 31.10% compared with CK,respectively.MD and HD treatments had extremely significant differences compared with CK,including HD and CK.Compared with the decline of more than 30%,the number of rhizobia will bedrastically reduced under severe drought.With the increase of drought degree,the number of lateral roots of soybeans was LD>MD>CK>HD.Under mild and moderate drought conditions,the number of lateral roots of soybeans increased.(8)Increased drought intensity caused a certain degree of decline in yield.Compared with CK,LD,MD,HD treatment,soybean yield per plant decreased by 18.59%,43.46%,54.89%,compared with CK in the MD,HD level decreased significantly,reaching a very significant difference.Compared with CK,under the treatments of LD,MD and HD,the100-grain weight of soybean decreased by 4.59%,12.80%,and 21.12%.Compared with CK,MD and HD achieved extremely significant differences(p<0.01).The number of stubble per plant,grain number per panicle,kernel weight per plant,yield per plant,weight of dry matter,and drought degree were all significantly negatively correlated.The correlation coefficient of 100-grain weight,yield per plant,and dry matter weight was-0.801**,-0.924**,-0.672**.