高大气CO2浓度下氮素对小麦叶片光能利用的影响

关于氮素对高大气CO₂浓度下C₃植物光合作用适应现象的调节机理已有较为深入的研究, 但对其光合作用适应现象的光合能量转化和分配机制缺乏系统分析。该文以大气CO₂浓度和施氮量为处理手段, 通过测定小麦(Triticum aestivum)抽穗期叶片的光合作用-胞间CO₂浓度响应曲线以及荧光动力学参数来测算光合电子传递速率和分配去向, 研究了长期高大气CO₂浓度下小麦叶片光合电子传递和分配对施氮量的响应。结果表明, 与正常大气CO₂浓度处理相比, 高大气CO₂浓度下小麦叶片较多的激发能以热量的形式耗散, 增施氮素可使更多的激发能向光化学反应方向的分配, 降低光合能量的热耗散速率; 大气CO₂浓度升高后小麦叶片光化学淬灭系数无明显变化, 高氮叶片的非光化学猝灭降低而低氮叶片明显升高, 施氮促进PSII反应中心的开放比例, 降低光能的热耗散; 高大气CO₂浓度下高氮叶片通过PSII反应中心的光合电子传递速率(J_F)较高, 而且参与光呼吸的非环式电子流速率(J₀)显著降低, 较正常大气CO₂浓度处理的高氮叶片下降了88.40%, 光合速率增加46.47%; 高大气CO₂浓度下小麦叶片J_F-J₀升高而J₀/J_F显著下降, 光呼吸耗能被抑制, 更多的光合电子分配至光合还原过程。因此, 大气CO₂浓度增高条件下, 小麦叶片激发能的热耗散速率增加, 但增施氮素后小麦叶片PSII反应中心开放比例提高, 光化学速率增加, 进入PSII反应中心的电子流速率明显升高, 光呼吸作用被抑制, 光合电子较多地进入光化学过程, 这可能是高氮条件下光合作用适应性下调被缓解的一个原因。

Effects of nitrogen application rates on photosynthetic energy utilization in wheat leaves under elevated atmospheric CO2 concentration

Aims It is well documented that the increment of nitrogen application rates leads to the release of photosynthesis acclimation of C₃ plants under elevated atmospheric CO₂ concentration. However, current knowledge of the effects of nitrogen application rates on photosynthetic electron transport and distribution and its potential influence on photosynthesis acclimation is inadequate. The objective of our potted-experiment was to study the effect of nitrogen application rates on photosynthetic electronic transports and distribution in wheat leaves under elevated atmospheric CO₂ concentration. Methods Using open-top chambers in simulating elevated atmospheric CO₂ concentration, we grew wheat (Triticum aestivum) under different nitrogen application rates and atmospheric CO₂ concentrations. We estimated the photosynthetic electron transport rate and its distribution by measurement of photosynthetic rate (P_n)-intercellular CO₂ concentration (C_i) curves and chlorophyll fluorescence parameters of  wheat leaves in the heading stage. Important findings Compared with ambient atmospheric CO₂ concentration treatments, more light energy excited by antenna pigments was dissipated as heat in wheat leaves under elevated atmospheric CO₂ concentration, the photochemical rate was increased and heat dissipative rate was decreased significantly in high-N wheat leaves. The non-photochemical quenching was decreased in high-N leaves but increased in low-N leaves, photochemical quenching coefficient was not changed significantly in both high-N and low-N leaves and the opening ratio of PSII reaction center would be increased and heat dissipation would be decreased where N was sufficient under elevated atmospheric CO₂ concentration. The photosynthetic electron rate of PSII (J_F) was increased, noncyclic electron transport rate involved in photorespiration (J₀) in high-N wheat leaves was decreased by 88.40% and J_F-J₀ increased and J₀/J_F decreased significantly under elevated atmospheric CO₂ concentration. Therefore, photorespiration was inhibited and more photosynthetic electrons were transported to photochemical process in wheat leaves under elevated atmospheric CO₂ concentration and the Pn was increased by 46.47%. We concluded that although more excited light energy of wheat leaves would be dissipated as heat under elevated atmospheric CO₂ concentration, the opening ratio of PSII reaction center, photochemical rates and JF increased, J₀ decreased where nitrogen was applied sufficiently and more photosynthetic energy was transported to photochemical process. This may be a reason why photosynthesis acclimation of C₃ plant is released in higher nitrogen content soil under elevated atmospheric CO₂ concentration.