Yield Formation Characteristics Of Rice Under Com-Bined Salinity-drought Stress

In this study,a pot experiment was carried out at the experimental farm of Yangzhou University in 2021 and 2022.Nanjing 9108 and Yandao 12,which were widely planted in Jiangsu Province,were used as experimental materials.The experimental treatments included the control(no stress,CK),single salinity stress(0.15s,soil salinity concentration 0.15%;0.3s,soil salinity concentration 0.3%),single drought stress(DH,drought at heading stage;DH15,drought 15 days after heading),and combined salinity-drought stress(0.15s+DH,0.15s+DH15,0.3s+DH,0.3s+DH15).The changes and differences of rice yield components,dry matter and nutrient accumulation and transport,plant morphology and leaf photosynthetic physiology under single salinity stress,single drought stress and combined salinity-drought stress were studied to clarify the effects of combined salinity-drought stress on rice yield formation and its morphological and physiological mechanism.The main results are as follows:1.Compared with the control,rice yield decreased significantly under single salinity stress,single drought stress,and combined salinity-drought stress.The decrease in rice yield under single salinity stress and combined salinity-drought stress was mainly due to the decrease in panicle number,spikelets per panicle,seed setting rate,and 1000-grain weight.The decrease in yield under single drought stress was mainly due to the decrease in seed setting rate and 1000-grain weight.Compared with the control,single salinity stress,single drought stress,and combined salinity-drought stress significantly reduced the number and weight of filled grains in the primary and secondary branches in the upper,middle,and lower parts of each panicle.The yield of rice under combined salinity-drought stress was significantly lower than that under single salinity stress and drought stress.The yield of Nanjing 9108 under combined salinity-drought stress(0.3s+DH,0.3s+DH15)was 36.4%and 20.7%lower than the single salinity stress(0.3s),respectively.Compared with single salinity stress and drought stress,the decrease of rice yield under combined salinity-drought stress was mainly caused by the significant decrease in seed setting rate and 1000-grain weight.Compared with single salinity stress and drought stress,the number and weight of filled grains in the primary and secondary branches in the upper,middle,and lower parts of each panicle decreased significantly under combined salinity-drought stress.2.Compared with the control,single salinity stress,single drought stress,and combined salinity-drought stress significantly reduced the dry weight of plants at maturity,and the dry weight of stems,leaves,and panicles also showed a similar trend.The dry matter weight of rice at maturity under combined salinity-drought stress was significantly lower than that under single salinity stress and drought stress.The dry weight of Nanjing 9108 under salinitydrought stress(0.15s+DH15,0.3s+DH15)was 26.5%and 53.6%lower than that of single drought stress(DH15).Compared with the control,the content and absorption of nitrogen,phosphorus,and potassium in rice decreased significantly under single salinity stress,single drought stress,and combined salinity-drought stress.The nitrogen(phosphorus and potassium)content and uptake of rice under combined salinity-drought stress were significantly lower than those under single salinity stress and drought stress,and the decrease of nitrogen and phosphorus uptake in stems and ears was the most pronounced.3.Compared with the control,salinity stress significantly reduced the plant height,the length and thickness of the first,second,and third internodes,and the length and width of the upper three leaves.Compared with the control,single salinity stress,single drought stress,and combined salinity-drought stress significantly reduced the net photosynthetic rate of leaves and the basal angles of the first,second,and third leaves.The net photosynthetic rate of rice and the basal angles of the first,second,and third leaves under combined salinity-drought stress were significantly lower than those under single salinity stress and drought stress.The net photosynthetic rate of Nanjing 9108 under combined salinity-drought stress(0.15s+DH,0.3s+DH)was 4.7%and 16.6%lower than that under single drought stress(DH),respectively.Compared with the control,the contents of chlorophyll a and b in rice leaves decreased significantly under single salinity stress,single drought stress,and combined salinity-drought stress.The activities of antioxidant enzymes(SOD,POD,CAT,and APX)in rice under combined salinity-drought stress were significantly lower than those under single salinity stress and drought stress.