Leaf Photosynthesis and Its Temperature Response Are Different between Growth Stages and N Supplies in Rice Plants.

Leaf photosynthesis is highly correlated with CO 2 -diffusion capacities, which are determined by both leaf anatomical traits and environmental stimuli. In the present study, leaf photosynthetic rate ( A ), stomatal conductance ( g s ), mesophyll conductance ( g m ) and the related leaf anatomical traits were studied on rice plants at two growth stages and with two different N supplies, and the response of photosynthesis to temperature ( T ) was also studied. We found that g m was significantly higher at mid-tillering stage and at high N treatment. The larger g m was related to a larger chloroplast surface area facing intercellular air spaces and a thinner cell wall in comparison with booting stage and zero N treatment. At mid-tillering stage and at high N treatment, g m showed a stronger temperature response. The modelling of the g m - T relationships suggested that, in comparison with booting stage and zero N treatment, the stronger temperature response of g m was related to the higher activation energy of the membrane at mid-tillering stage and at high N treatment. The findings in the present study can enhance our knowledge on the physiological and environmental determinants of photosynthesis.