The Effects of Drought and Heat Stress on the Photosynthetic Characteristics of Alfalfa

With the global weather becoming warmer,the drought and heat has become more and more severe.In order to understand the change of photosynthetic characteristics under drought and heat stress,the effects of drought and heat stress on the leaf net photosynthetic rate(P_n),transpiration rate(T_r),intercellular CO_2 concentration(C_i),stomatal conductance(G_s),water use efficiency(WUE) of six alfalfa(Medicago saliva L.) cultivars were studied.Results showed that the leaf net photosynthetic rate,transpiration rate,stomatal conductance,water use efficiency of all tested cultivars decreased with the increase of drought and heat stress,while the intercellular CO_2concentration increased(P0.05).The transpiration rate and stomatal conductance of WL525 recovered obviously after(P0.05) rehydration,whereas the net photosynthetic rate,intercellular CO_2 concentrtion,water use efficiency of all tested cultivars were not improved significantly after rehydration.Correlation analyses showed that the net photosynthetic rate had significantly positive correlation with the transpiration rate,stomatal conductance,water use efficiency of alfalfa under drought and heat stress(P0.01),but had significantly negative correlation with the intercellular CO_2 concentration(P0.01).