Effect of Nitrogen Nutrition on Photosynthetic Function of Wheat Leaf Under Elevated Atmospheric CO2 Concentration

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 C3 plant, and its influence on photosynthesis function in wheat leaves under elevated [CO2]. Using the top open chambers to simulate the elevated atmospheric CO2 concentration, wheat plants were fertilized with high and low amounts of N, and were grown under atmospheric CO2 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 CO2 concentration, the photosynthesis acclimation appeared in the low-N treatment, such as decreases of photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), photochemical rate, photosynthetic electron rate of PS II (JF), photosynthetic linear electron to carboxylation (Jc), Rubisco carboxylase rate (Vc), and triose phosphate utilization (TPU). However, these changes were not observed in the high-N treatment. The values of Jc/JF, Vc/Jc, and Vo/Vc had no significant changes between N treatments, and elevated CO2 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 CO2 concentration. This suggested that the photosynthetic energy transport rate and assimilatory ability were promoted by N application under elevated CO2 concentration. This is a reason for no photosynthesis acclimation in high-N treatment under elevated CO2 concentration. Significant interaction on photosynthetic energy use in wheat leaves was observed between N application rate and atmospheric CO2 concentration. At heading stage, with application of N, the photosynthetic NUE was increased under elevated CO2 concentration, but decreased under ambient CO2 concentration. These results showed a direct effect of N application on wheat photosynthesis under elevated atmospheric CO2 concentration.

摘 要为探讨高大气CO2浓度下植物光合作用适应现象的光合能量转化和分配的氮素响应及其对C3植物光合功能的影响, 本试验对盆栽小麦进行2个大气CO2浓度和2个氮水平的组合处理, 通过测定小麦光合气体交换参数、叶绿素荧光参数和叶绿素含量等指标, 研究施氮对高大气CO2浓度下小麦叶片光合功能的影响。结果表明, 大气CO2浓度升高后, 低氮处理小麦叶片光合速率发生明显的适应性下调, 光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)下降; 但高氮叶片则无明显的光合作用适应现象发生。高大气CO2浓度下低氮叶片光化学速率、PSII线性电子传递速率(JF)、光合电子流的光化学传递速率(JC)、Rubisco羧化速率(VC)和TPU下降, 并随生育时期推进其下降趋势更为明显, 但高氮叶片的上述参数无显著变化; 小麦叶片JC/JF、VC/JC和VO /VC随氮素水平和大气CO2浓度的变化无显著变化, 表明施氮能提高光合机构对光合能量的传递速率, 但对光合能量的分配方向无明显影响。施氮提高小麦叶片氮素和叶绿素含量, 并且使高大气CO2浓度下光合氮素利用效率(NUE)明显增加。大气CO2浓度升高后, 施氮增强光合机构的光合能量运转速率, 同化力提高, 无明显的光合作用适应现象; 由于氮素水平与大气CO2浓度对小麦叶片的光合能量利用存在明显的交互作用, 而且高大气CO2浓度下施氮使得小麦叶片NUE增加、正常大气CO2浓度下降低, 证明高大气CO2浓度下施氮对光合作用具有直接的影响。