Fig. 5 Correlation analysis between photosynthetic indexes and their influencing factors Pn: net photosynthetic rate, Tr: transpiration rate, Gs: stomatal conductance, Ci: intercellular CO2 concentration, WUEL: water use efficiency of leaf, θ: soil moisture content in 0-60 cm soil layer, Tl: leaf temperature, S: solar radiation intensity, Ta: ambient temperature, RH: relative humidity of atmosphere. * indicates significant correlation at the 0.05 probability level.