Effects of nitrogen application rate on light-response curves of flag leaves in super-high yielding winter wheat at grain filling stage

In order to provide a standard consortium for nitrogen fertilizer management of super-high yielding winter wheat cultivation, different nitrogen application rates were tested in concomitant with their effects on light-response curves in the flag leaves were studied. The experiments were conducted at grain filling stage of super-high yielding winter wheat under field conditions. Net photosynthetic rate (Pn), stomatal conductance ( Gs) , intercellular CO₂ concentration (Ci) and transpiration rate (Tr) in flag leaves of super-high yielding winter wheat were measured in an open-circuit gas channel system. Moreover, Pn was simulated by the Michaelis-Menten model, and then characteristic parameters of the light response curves were calculated. The results showed that Pn, Gs and Tr of flag leaves among all treatments increased with the increasing of the light intensity in the range of 0-300 kg/hm² nitrogen application rate, but Ci decreased. However, the increasing of Pn, Gs and Tr and the decreasing of Ci under the nitrogen level of 375 kg/hm² were lower than that under the nitrogen level of 300 kg/hm², which indicated that reasonable nitrogen application has significant regulating effect on light-response curves of flag leaves in super-high yielding winter wheat at grain filling stage. It can be concluded that at the rational range of nitrogen application, the maximum net photosynthetic rate ( Pn_max) of the flag leaves with high yield increased in the whole grain filling stage with the increasing of nitrogen fertilizer. Under this experiment condition (N 300 kg/hm² application), the highest grain yield was observed and hence suggested for super-high yielding winter wheat cultivation.