Leaf Temperature and Vapour Pressure Deficit (VPD) Driving Stomatal Conductance and Biochemical Processes of Leaf Photosynthetic Rate in a Subtropical Evergreen Coniferous Plantation

Photosynthesis is arguably the most important biochemical process on Earth, which is dramatically influenced by environmental conditions. How environmental factors drive stomatal conductance and biochemical processes of leaf photosynthetic rate has not been sufficiently investigated in subtropical China. In this study, we analysed the effects of stomatal and biochemical parameters on the photosynthetic rate of native Masson’s pine (Pinus massoniana Lamb.) and exotic slash pine (Pinus elliottii Engelm.) in response to leaf temperature and vapour pressure deficit (VPD) in subtropical China, based on leaf gas exchange measurements in 2016. Our results showed that there was no significant difference in the light-saturated photosynthetic rate (Asat) between native Masson’s pine and exotic slash pine. The seasonal patterns of maximum rate of the carboxylation (Vcmax25) were basically consistent with seasonal patterns of Asat for both species. The positive effect of leaf temperature on Asat was mainly produced through its positive effect on Vcmax25. Leaf temperature had no significant effect on stomatal conductance. Vcmax25 and gs simultaneously affected Asat in response to VPD. Our results highlighted the importance of biochemical processes in limiting leaf photosynthetic rate in response to environmental conditions in subtropical evergreen coniferous plantations