Characteristics of rice leaf photosynthetic light response curve with different water and nitrogen regulation

In order to reveal the influence of soil moisture and nitrogen regulation on characteristics of rice leaf photosynthetic light response pots experiments were carried out. Leaf photosynthetic light response curves were measured in later tillering stage and booting-jointing stages, under different soil moisture conditions with two nitrogen levels. With soil moisture depletion, photosynthetic light response curves reduced, especially when the photosynthetic photon flux density was higher than 400 μmol/(m2·s). Parameters derived from photosynthetic light response model indicated maximum photosynthesis rate Pnmax and light saturation points LSP reduced with decrease in soil moisture, and recovered after rewetting. Reduced nitrogen inputs were likely aggravating the reduction in photosynthetic light response curves, Pnmax and LSP. It can be concluded that water stress leads to inhibition on adaptive capacity of rice leaf photosynthesis to strong light, which would be recovered after rewetting. High nitrogen inputs, within the range of 200-300 kg/hm2, can be helpful to improve leaf photosynthetic light response characteristics, and enhance the recovery and compensation effects. Criteria of soil moisture regulation for rice water saving irrigation should be determined according to different nitrogen levels in rice paddy.