Responses of leaf gas exchange to high temperature and drought combination as well as re-watering of winter wheat under doubling atmospheric CO_2 concentration
Understanding the responsible mechanisms of crops to combined environmental stresses such as elevated CO_2 concentration,climate warming,and drought is critical to improve the accuracy of ecological process models,and thus accurately predict the impacts of global climate change on the Net Primary Production (NPP) and ecosystem service function of farmlands.Four environmental growth chambers accurately controlling CO_2 concentration and temperature were employed to investigate the combined effects of high temperature and drought stresses on the stomatal traits and leaf gas exchange during re-watering under doubling CO_2 concentration.We found that elevated CO_2 concentration (E) increased the stomatal density,decreased the stomatal width and made the spatial distribution pattern of stomata irregular on the abaxial leaf surface,while enhanced the net photosynthetic rates (P_n),stomatal conductance (G_s),transpiration rates (T_r),and water use efficiency (WUE).The stomatal length,width,perimeter and area were substantially decreased under the combined high temperature and drought stress (HD),resulting in dramatic decline of leaf gas exchange parameters.Doubling CO_2 concentration made the leaf gas exchange parameters enhanced under the HD treatment,suggesting that elevated CO_2 concentration can compensate the negative impacts of heat and drought on the physiological processes of winter wheat.Additionally,the leaf gas exchange of winter wheat subjected to the high temperature and drought stresses was enhanced after re-watering,but these parameters were still lower than those of Control,suggesting that the photosynthetic apparatus may be damaged by the combined high temperature and drought stresses.