Effect of Nitrogen Nutrition on Photosynthetic Function of Wheat Leaf Under Elevated Atmospheric CO 2 Concentration

Abstract

The objectives of this study was to understand the responses of photosynthetic electron transport and partition of photosynthesis acclimation to nitrogen (N) application rate in C 3 plant, and its influence on photosynthesis function in wheat leaves under elevated [CO 2]. Using the top open chambers to simulate the elevated atmospheric CO 2 concentration, wheat plants were fertilized with high and low amounts of N, and were grown under atmospheric CO 2 concentration of 400 μmol mol −1 (ambient concentration) or 760 μmol mol −1 (elevated concentration). The photosynthetic gas exchange parameters, chlorophyll fluorescence parameters, and nitrogen and chlorophyll content of wheat leaves were measured at the jointing and heading stages. Under elevated CO 2 concentration, the photosynthesis acclimation appeared in the low-N treatment, such as decreases of photosynthetic rate ( P n), stomatal conductance ( G s), transpiration rate ( T r), photochemical rate, photosynthetic electron rate of PS II ( J F), photosynthetic linear electron to carboxylation ( J c), Rubisco carboxylase rate ( V c), and triose phosphate utilization (TPU). However, these changes were not observed in the high-N treatment. The values of J c/ J F, V c/ J c, and V o/ V c had no significant changes between N treatments, and elevated CO 2 concentration caused no significant changes on these parameters neither. This result indicated that N application may increase photosynthetic energy use rather than influence photosynthetic energy distribution. The contents of leaf N and chlorophyll were higher in the high-N treatment than those in the low-N treatment, resulting in the increase of photosynthetic nitrogen use efficiency (NUE) in high-N wheat flag leaves under elevated CO 2 concentration. This suggested that the photosynthetic energy transport rate and assimilatory ability were promoted by N application under elevated CO 2 concentration. This is a reason for no photosynthesis acclimation in high-N treatment under elevated CO 2 concentration. Significant interaction on photosynthetic energy use in wheat leaves was observed between N application rate and atmospheric CO 2 concentration. At heading stage, with application of N, the photosynthetic NUE was increased under elevated CO 2 concentration, but decreased under ambient CO 2 concentration. These results showed a direct effect of N application on wheat photosynthesis under elevated atmospheric CO 2 concentration.