Study on the photosynthetic characteristics of Elymus excelsus.

The ecophysiological photosynthetic characteristics of Elymus excelsus leaves and their environmental factors were measured using Li-6400 portable photosynthesis system.The relationship between the net photosynthetic rate(Pn) and leaf transpiration(Tr) and its physio-ecological factors were studied by correlation and stepwise regression equation.The results showed that:(1) the diurnal change of Pn presented a bimodal pattern,and had a clear midday depression.The diurnal variation patterns of Tr and stomatal conductance(Gs) were also bimodal.The peak values of water deficit(VPD),Gs and Tr appeared asynchronous.Intercellular CO2 concentration(Ci) did not decrease with the dropping of stomatal conductance.The mainly controlling factor of photosynthetic rate was non-stomatal limitation.The diurnal variation of water use efficiency(WUE) was one-peak curve,and the WUE of morning was significantly higher than that of the afternoon.(2)Under the natural condition,Tr and Ca(air CO2 concentration) were the key factors that affected the changes of Pn and the main factors that affected Tr were Gs and Ta(air tempreture).(3)The light compensation point(LCP) of photosynthesis of Elymus excelsus in leaves was 12.45 μmol·m-2·s-1.The light saturation point(LSP) of photosynthesis was 1 750 μmol·m-2·s-1,the maximum Pn was 65.125 μmol·m-2·s-1.The apparent quantum yield was 0.128 9 μmol·mol-1.Elymus excelsus is adaptable widely to photo flux density and is a typical heliophyte.