Response of rice yield formation to combined salinity-drought stress and its physiological mechanism
This research was designed as a pot experiment with conventional japonica rice Nanjing 9108 and Huaidao 5,which are widely planted in the coastal saline areas of Jiangsu.The experiment was conducted at 0.3％soil salt con-centration,and set drought stress(soil water potential-25 kPa)from jointing to heading with salinity-and drought-free as control(CK).This study was conducted to identify response characteristics of rice yield formation to combined salinity and drought stress of the two varieties.Under single salinity stress,single drought stress,and combined salinity-drought stress,rice average yield of the two varieties decreased by 114.8％,39.6％,and 154.2％compared to the control,re-spectively.The average yield of the two varieties under combined salinity-drought stress was significantly lower than that under single salinity stress and single drought stress,with a decrease of 18.6％and 82.2％respectively.Compared with single salinity stress and single drought stress,the decrease in rice yield under combined salinity-drought stress was main-ly due to a significant decrease in spikelets per panicle,filled-grain percentage,and 1000-grain weight.Compared with the control,single salinity stress,single drought stress,and combined salinity-drought stress significantly reduced the dry matter weight of plants at heading and maturity stages,as well as the net photosynthetic rate and chlorophyll(a+b)con-tent of leaves at 20 days after jointing and 20 days after heading,and increased the rice harvest index.Under combined sa-linity-drought stress,dry matter weight at heading and maturity,and the net photosynthetic rate and chlorophyll(a+b)content of leaves at 20 days after jointing and 20 days after heading of plants were significantly lower than those under sin-gle salinity stress and single drought stress;the harvest index showed the opposite trend.Under single salinity stress,single drought stress,and combined salinity-drought stress,the activities of superoxide dismutase(SOD),catalase(CAT),and ascorbate peroxidase(APX)enzymes in rice leaves at 20 days after jointing and 20 days after heading were significantly lower than those of the control;the content of malondialdehyde(MDA)and hydrogen peroxide(H2O2)in leaves showed an opposite trend.Compared with single salinity stress and single drought stress,the activities of SOD,CAT,and APX enzymes in leaves at 20 days after jointing and 20 days after heading significantly decreased under com-bined salinity-drought stress,while the content of MDA and H2O2 in leaves significantly increased.This study demon-strated that compared to single salinity stress and single drought stress,combined salinity-drought stress significantly in-hibited the photosynthetic performance of rice plants,thereby affecting the accumulation and allocation of photosynthetic assimilates,ultimately leading to a significant decrease in sink size and sink-filling efficiency,and rice yield.The decrease in rice yield caused by combined salinity-drought stress was significantly higher than that caused by single salinity stress and single drought stress,and its inhibitory effect on rice yield had a superimposed effect.
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