Analysis on relationship between diurnal changes of photosynthetic and transpiration rate of three alfalfa varieties and related factors during the branching stage

Under natural conditions,the diurnal changes of photosynthetic and transpiration rate of three alfalfa varieties(WL-232,WL-323,WL-525) and related physiological and ecological factors during the branching stage of the first harvest in the third year were measured by using CI-340 portable photosynthesis system.The ecological factors included photosynthetic available radiation(PAR),air temperature(Ta),CO2 concentration in field(Ca),temperature and relative humidity(RH).The physiological factors included leaf temperature(Tl),stomatal conductance(Cs) and internal CO2 concentration.Relative analysis and path coefficient analysis were used to discuss how related factors influenced diurnal changes of photosynthetic and transpiration rate.The results showed that WL-232 was high photosynthetic,high water using and low transpiration variety.The net photosynthetic rate of the three varieties appeared to vary in a double-peak curve,and the midday depression mainly resulted from non-stomatal factors.Path coefficient analysis showed that Ta was the primary ecological determining factor for the characteristics of photosynthesis and transpiration;RH was the main limiting factor for the characteristic of photosynthesis;Ca was the main limiting factor for the characteristic of transpiration of WL-232,and PAR was the main limiting factor for the characteristic of transpiration of WL-323 and WL-525.The main physiological factor affecting the characteristic of photosynthesis of alfalfa was Ci,Cs was the main limiting factor,and Tl was the main physiological factor affecting the characteristic of transpiration of alfalfa.