Nitrogen can improve the rapid response of photosynthesis to changing irradiance in rice (Oryza sativa L.) plants

To identify the effect of nitrogen (N) nutrition on the dynamic photosynthesis of rice plants, a pot experiment was conducted under two N conditions. The leaf N and chlorophyll levels, as well as steady–state photosynthesis, were significantly increased under high N. After the transition from saturating to low light levels, decreases in the induction state (IS%) of leaf photosynthesis (A) and stomatal conductance (g(s)) were more severe under low than under high N supply. After the transition from low to flecked irradiance, the times to 90% of maximum A (T(90%A)) were significantly longer under low than under high N supply. Under flecked irradiance, the maximum A under saturating light (A(max–fleck)) and the steady–state A under low light (A(min–fleck)) were both lower than those under uniform irradiance (A(sat) and A(initial)). Under high N supply, A(max–fleck) was 14.12% lower than A(sat), while it was 22.80% lower under low N supply. The higher IS%, shorter T(90%A), and the lower depression of A(max–fleck) from A(sat) under high N supply led to a less carbon loss compared with under a low N supply. Therefore, we concluded that N can improve the rapid response of photosynthesis to changing irradiance.