Vertical profile of photosynthetic CO response within rice canopy.

Leaf-specific Farquhar-von Caemmerer-Berry (FvCB) model was fitted to characterize the vertical profile of photosynthetic CO response within rice canopy. Leaf-position-specific and canopy average FvCB models were fitted to study a suitable leaf representing photosynthetic parameters at the canopy scale. The results showed that leaf photosynthesis was limited by Rubisco activity or ribulose-1,5-bisphosphate regeneration under field conditions. The maximum rate of carboxylation, maximum rate of electron transport, rate of triose phosphates utilization, and light respiration rate in the FvCB model reached the highest values for the top second leaf and then decreased, while the mesophyll diffusion conductance kept decreased in downward leaves. The integrated photosynthetic CO-response curves for the top fourth and fifth leaves were appropriate for estimating parameters in the FvCB model at the canopy scale.