| As the two most common environmental factors that affect photosynthesis of crops,high temperature and drought seriously impact on agricultural production activities.In the context of global warming,it is increasingly urgent to explore the impact of high temperature and drought on crops.This study carried out field experiments to deeply analyze the mechanism of influence of combined heat and drought stress on winter wheat morphology,physiology and photosynthesis from March to May 2022.Meanwhile,the response of Solar-Induced Chlorophyll Fluorescence on high-temperature drought combined stress was explored.Then,the correlation mechanism between morphology,physiology,photosynthesis of winter wheat and canopy SIF under high-temperature drought combined stress was also revealed.Finally,the influence mechanism of winter wheat yield under high-temperature drought combined stress was studied,and the prediction analysis of winter wheat yield based on canopy SIF was conducted.The main research conclusions are as follows:(1)The growth rate of winter wheat plant height treated with normal water supply was significantly faster than that treated with stress.At the same time,the leaf area generally increased first and then decreased.The variation regularities of chlorophyll content and LWC in winter wheat were basically the same,showing a general trend of first rising and then declining.The diurnal variation of net photosynthetic rate(P_n)of winter wheat showed a bimodal variation;and the GPP showed a trend of first increasing and then decreasing in the whole growth period.Under high temperature and drought stress,there were significant differences in the morphological,physiological and photosynthetic parameters of winter wheat in each stress treatment plots,among which the effects of drought stress were more serious than those of high temperature stress,the effects of severe drought stress were greater than those of moderate drought stress,and the inhibition effects were more obvious with the intensification of stress.(2)On the daily scale,the SIF curve of winter wheat canopy showed a similar"unimodal"variation,and the canopy SIF showed a trend of first increasing and then decreasing at different growth stages.The overall performance of each treatment plot was similar to the diurnal variation curve of SIF,indicating that drought and high temperature stress could inhibit the canopy SIF phenomenon.The more severe the stress,the more severe the canopy SIF response.The linear fitting results of winter wheat canopy SIF,LWC,chlorophyll content and photosynthetic parameters were significantly positive under different degrees of high temperature and drought stress,and the greater the drought(high temperature)stress,the smaller the R~2.(3)With the aggravation of high temperature and drought stress,the sterility ratio of winter wheat increased,and the grain number per plant and 1000-grain weight of winter wheat decreased to different degrees.The overall effect of severe drought stress was greater than that of moderate drought stress.There was a significant positive correlation between canopy SIF and 1000-grain weight data of winter wheat,and the R~2 of linear fitting results showed high significance in different growth periods.There was a high correlation between canopy SIF and yield under different drought(high temperature)stress,and the R~2 of canopy SIF under severe drought(high temperature)stress was lower than that under no drought(high temperature)stress.According to the analysis of random forest model and linear regression model,physiological data,environmental data and canopy SIF of winter wheat were highly correlated with their yield data,and the linear fitting R~2 of predicted and measured yield of random forest model was 0.9084.The linear fitting R~2 of the predicted yield and measured yield of the mathematical model of multiple linear regression analysis was 0.9249,which showed a high correlation,proving that canopy SIF has a certain possibility in predicting winter wheat yield. |
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