高大气CO2浓度下氮素对小麦叶片光合能量分配的调节

探讨了施氮量对高大气CO₂浓度下小麦功能叶光合能量传递与分配的影响，进而明确氮素对小麦叶片光合作用适应性下调的能量分配调节作用。采用开顶式气室盆栽法，通过测定小麦拔节期和抽穗期不同大气CO₂浓度和施氮水平下的叶氮浓度、光合速率–胞间CO₂浓度(P_n–C_i)响应曲线和荧光动力学参数，测算光合电子传递速率和分配去向。与在正常CO₂浓度(400 μmol mol^-1)条件下相比，在高大气CO₂浓度(760 μmol mol^-1)下，小麦叶氮浓度显著下降，N200处理(200 mg kg^-1)叶片抽穗期叶氮浓度的下降幅度较拔节期高335.7%。N200处理较N0处理(0 mg kg^-1)提高小麦叶片光适应下PSII反应中心最大量子产额(F_v′/F_m′)、光化学效率(Φ_PSII)和开放比例(q_P)，降低非光化学猝灭系数(NPQ)。高大气CO₂浓度下，小麦叶片光化学反应的非环式光合电子传递速率(J_c)和Rubisco羧化速率(V_c)显著升高，而光呼吸的非环式光合电子传递速率(J_o)和Rubisco氧化速率(V_o)明显降低；施氮使J_c、J_o、V_c和V_o值均呈上升趋势，而且J_c和V_c达到显著差异。高大气CO₂浓度下J_o/J_c和V_o/V_c显著降低，施氮后小麦拔节期叶片J_o/J_c和V_o/V_c降低，但抽穗期J_o/J_c升高而V_o/V_c无明显变化。叶氮浓度与小麦叶片J_c、J_o和V_o均呈显著线性正相关，而且高大气CO₂浓度下小麦叶片J_c、J_o和V_o对氮浓度的敏感性降低。高大气CO₂浓度下，小麦叶片PSII反应中心开放比例增加，非光化学耗能降低，更多的光合电子进入光化学过程；施氮后使小麦叶氮浓度增加，提高光合能力，改变了能量分配，这是高氮条件下光合作用适应性下调被缓解的一个关键因素。

Regulation of Nitrogen Level on Photosynthetic Energy Partitioning in Wheat Leaves under Elevated Atmospheric CO2 Concentration

The objective of this study was to understand the regulatory mechanism of nitrogen (N) application on photosynthetic acclimation under elevated atmospheric CO₂ concentration. The ambient atmospheric CO₂ concentration was 400 μmol mol^?1, and the elevated CO₂ concentration was 760 μmol mol^?1, which was simulated with Top Open Chambers. Wheat (Triticum aestivum L.) cultivar Ningchun 4 was grown in pots under both CO₂ concentrations and treated with low (0 mg pure N per kilogram soil, N0) and high (200 mg pure N per kilogram soil, N200) N application levels. The photosynthetic electron transport rate was estimated using the response curve between photosynthetic rate (P_n) and intercellular CO₂ concentration (C_i) and chlorophyll fluorescence parameters. The leaf nitrogen concentrations were also measured at jointing and heading stages. Compared to that under the ambient CO₂ concentration, the leaf nitrogen concentration of wheat was decreased significantly under the elevated CO₂ concentration, and the percentage of decrease in N200 treatment was 335.7% higher at heading than jointing stage. The values of maximal quantum yield under irradiance (F_v′/F_m′), actual PSII efficiency under irradiance (Φ_PSII), photochemical fluorescence quenching (q_P) were higher in N200 treatment than in N0 treatment; however, the value of non-photochemical fluorescence quenching (NPQ) was higher in N0 treatment than in N200 treatment. Under elevated atmospheric CO₂ concentration, the electronic transport rate of photochemistry (J_c) and Rubisco carboxylation rates (V_c) were increased significantly, but the electronic transport rate of photorespiration (J_o) and Rubisco oxygenation rate (V_o) were decreased significantly. N application tended to promote the values of J_c, J_o, V_c, and V_o, especially for J_c and V_c, which had significant increase compared to those in N0 treatment. When the atmospheric CO₂ concentration elevated from 400 μmol mol^?1 to 760 μmol mol^?1, the rations of J_o/J_c and V_o/V_c decreased significantly. Under the elevated atmospheric CO₂ concentration, N application decreased J_o/J_c and V_o/V_c significantly at jointing stage, but increased J_o/J_c at heading stage and remained V_o/V_c with no significant difference. The leaf nitrogen concentration was positively correlated with J_c (P < 0.01), J_o, (P < 0.05) and V_o (P < 0.05), and the sensitivities of J_c, J_o, and V_o in response to leaf N concentration were decreased under elevated atmospheric CO₂ concentration. The opening ratio of PSII reaction center was increased under elevated atmospheric CO₂ concentration, and the non-photochemical energy dissipation was decreased simultaneously, resulting in more photosynthetic electron transported to photochemical process in wheat leaf. N application had a positively effect on photosynthetic function and changed its energy partitioning through increasing leaf N concentration. This might be one of the key reasons for photosynthesis acclimation of C₃ plant to N sufficient application under elevated atmospheric CO₂ concentration.