氮素对高大气CO2浓度下小麦叶片光合功能的影响

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(P_n)、气孔导度(G_s)、蒸腾速率(T_r)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(J_F)、光合电子流的光化学传递速率(J_C)、Rubisco羧化速率(V_C)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J_C/J_F、V_C/J_C和V₀ /V_C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。

Effects of Nitrogen Nutrition on Photosynthetic Functions of Wheat Leaves under Elevated Atmospheric CO2 Concentration

Nitrogen application rate is a critical factor led to photosynthesis acclimation of C₃ plant under elevated atmospheric CO₂ concentration. However, current knowledge is inadequate for the responses of photosynthetic electron transport and energy distribution of photosynthesis acclimation to nitrogen application rate in C₃ plant, and the influence of photosynthesis function on photosynthetic electron transport and energy distribution. Using Top Open Chambers, the elevated concentration of atmospheric CO₂ was simulated. Wheat (Triticum aestivum L.) was grown under two nitrogen application rates and two atmospheric CO₂ concentrations. The photosynthetic gas exchange parameters, chlorophyll fluorescence parameters, and chlorophyll content of wheat leaves, were measured at jointing and heading stages to study the influence of nitrogen application on photosynthetic function of wheat leaves exposed to elevated atmospheric CO₂ concentration. The results showed that the photosynthetic rate (P_n), stomatal conductance (G_s), and transpiration rate (T_r) decreased in low-N wheat leaves, and the photosynthetic acclimation appeared. However, in high-N wheat leaves the photosynthetic acclimation did not appear, P_n, G_s, and T_r decreased significantly whereas the leaf WUE increased significantly under elevated atmospheric CO₂ concentration. The photochemical rate, photosynthetic electron rate of PSII (J_F), electronic transport rate of photochemistry (J_C), Rubisco carboxylase rate (V_C), and triose phosphate utilization (TPU) declined significantly in low-N wheat leaves; and were not changed in high-N wheat leaves compared to those under ambient atmospheric CO₂ concentration. The J_C/J_F, V_C/J_C, and V₀/V_C had no significant changes between treatments with different nitrogen application rate and atmospheric CO₂ concentrations. This indicated that nitrogen application may increase the photosynthetic energy use, but have no significant influence on photosynthetic energy distribution. The leaf nitrogen and chlorophyll contents increased when nitrogen was applicated under both treatments of CO₂ concentrations, especially, the photosynthetic nitrogen use efficiency (NUE) in high-N wheat leaves increased under elevated atmospheric CO₂ concentration. It suggested that the photosynthetic energy transport rate and assimilatory ability increased by nitrogen application under elevated atmospheric CO₂ concentration. Thus, the photosynthesis acclimation did not appear in high-N wheat leaves. Because there was a significant interaction between nitrogen application rate and atmospheric CO₂ concentration on photosynthetic energy use in wheat leaves, and the photosynthetic NUE in high-N wheat leaves increased under elevated atmospheric CO₂ concentration but decreased under normal ambient atmospheric CO₂ concentration, it concluded that the nitrogen application affects photosynthesis directly in wheat leaves under elevated atmospheric CO₂ concentration.