Diurnal Dynamics of Photosynthetic Parameters in Leaves of Ningxia ZiZyphus jujube and Its Relation to Environmental Factors

During the full-bloom stage of Ningxia ZiZyphus jujube,the diurnal dynamics of photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs)and internal CO2(Ci),as well as the ecological factors photosynthetically active radiation(PAR),CO2 concentration in field(Ca),relative humidity(RH),air temperature(Ta)and lear temperature(Tl)were measured.The results showed that the diurnal net photosynthetic rate of ZiZyphus jujube in sunny day exhibited double-peak pattern.There was a significant midday depression with ZiZyphus jujube,which was caused principally by stomatal factors such as stomatal conductance.The curves of diurnal variation in Tr,Gs and Ci of ZiZyphus jujube leaves also had two peaks.The most optimal equation describing diurnal variation of Pn was attained by the method of stepwise multiple—regression as follows:YPn=-49.168-0.002 21 xPAR+1.776 xTa-0.445 xTl+0.003 736 xCi+0.67 xRH(R2=0.994,P0.05).With the analysis of partial correlation and path on Pn and environmental factors,it was concluded that Ta and RH had the greatest effect on the diurnal dynamics of Pn,while other factors indirectly affected Pn.