Effects Of Drought Stress/Rewatering At Different Growth Stages On Photosynthetic Characteristics,Yield And Quality Of Soybean

Under global climate change,the frequency and intensity of drought increase,which would greatly affect soybean production.Studies on photosynthetic characteristics and yield of soybean under different levels of drought stress/rewatering at different growth stages could help clarify the impacts of drought on soybean growth and the underlying mechanisms.Taking Liaodou 15 as the research object,the experiment was conducted at the crop cultivation scientific observation and test station in the northeast of the Ministry of agriculture and rural areas in 2020,and the water control experiments were conducted at the flowering stage and full seed stage in the soybean plots,respectively.The water stress level was set as mild drought（65%field capacity）and severe drought（50%field capacity）and lasted for 7,14and 21 days.Rewatering was carried out after drought,and the rewatering level was equal the control treatment level（80%field capacity）.The photosynthetic,yield and quality indexes of soybean were measured,and the effects of drought stress on photosynthetic characteristics,yield and quality of soybean were analyzed.The main research results are as follows:（1）Drought stress at flowering stage and full seed stage reduced the maximum net photosynthetic rate(P_max)of soybean by 19.56-70.86%and 44.38-74.03%,respectively.At the flowering stage,the decrease of net photosynthetic rate（P_n）was dominated by the stomatal factor.While at the full seed stage,the P_n decreases induced by water stress shifted from stomatal to non-stomatal dominated during the full seed stage.With the increase of drought stress intensity and duration,the stomatal conductance of soybean leaves decreased and the transpiration rate of soybean leaves decreased at flowering stage and full seed stage,and could not return to CK level after rewatering.When the duration of drought stress was short（7-14 days）,the water use efficiency（WUE）of soybean increased 6.88-52.34%.Whereas the drought lasted for longer time（21 days）,the WUE decreased by 20.41-61.18%.The WUE could be elevated by short-term drought,whereas the WUE decreased when the drought lasted for longer time.（2）With the increase of drought stress intensity and duration,the number of grains per plant,the number of pods per plant,the weight of pod skin and 100 seeds per plant decreased at flowering and full seed stage,while the number of grains per plant and the rate of pods per plant increased,Drought led to a decrease in yield loss of soybean.Moreover,the drought with same intensity had greater effects on soybean yield at the full seed stage than at the flowering stage.Drought reduced the yield by 15.63-55.47%when drought occurred at the flowering stage and24.17-59.63%at the full seed stage.（3）Drought stress increased the protein content and decreased the fat content of soybean.The effect of drought stress on the protein and fat content of soybean in full seed stage was greater than that in flowering stage.With the increase of drought stress intensity and duration,in the flowering stage of soybean,the protein content increased by 2.06-5.05%,and the fat content decreased by 0.87-4.77%,and in the full seed stage of soybean,the protein content increased by 2.37%-5.26%,and the fat content decreased by 1.75-6.42%.