运用LI-6400便携式光合作用系统测定了不同光强(2000、1500、1000和500 μmol·m^-2·s^-1)和两种O₂浓度(21%和2%的O₂)下冬小麦(Triticum aestivum)灌浆期旗叶的CO₂响应曲线, 比较了现有CO₂响应模型(生化模型、直角双曲线模型和直角双曲线修正模型)拟合给出光下(暗)呼吸与测量值之间的差异。结果显示, 直角双曲线修正模型所给出的光下呼吸速率拟合值与测量值最为接近。植物光合作用对大气CO₂响应(A/C_a)的拟合结果优于光合作用对胞间CO₂浓度(A/C_i)的拟合。然而, 所有模型基于A/C_a拟合的光下(暗)呼吸在整体上与测量值存在显著差异(p < 0.05), 推测与现有模型没有考虑CO₂浓度对光呼吸和光下暗呼吸速率的影响有关。对小麦的试验结果表明, CO₂浓度对光呼吸和光下暗呼吸均有显著影响: 随着CO₂浓度的增加(0-1400 μmol·mol^-1), 不同光强下的表观光呼吸变化范围分别为5.035-11.670、4.222-11.650、4.330-10.999和3.263-9.094 μmol CO_2·m^-2·s^-1; 光下暗呼吸的变化范围分别为0.491-2.987、0.457-2.955、0.545-3.139和0.448-3.139 μmol CO₂·m^-2·s^-1。回归分析发现, 表观光呼吸和光下暗呼吸与CO₂浓度之间均存在较好的相关性。然而, 将该回归关系整合到现有模型中, 是否会优化模型, 从而提高模型对相关光合参数估算的准确性尚有待于进一步研究。

Aims The objective of this study was to compare the values of respiration under light derived by fitting a photosynthetic CO₂ response model and measurements, in order to provide information for model optimization.

Methods Using combined gas exchange measurements and a low O₂ (2% O₂) method, the responses of photosynthetic rate (P_n) to CO₂ at different light intensities (2000, 1500, 1000 and 500 μmol·m^-2·s^-1) in the flag leaves of wheat were measured. The measured data were fitted by a biochemical model, a rectangular hyperbola model and a modified rectangular hyperbola model of the photosynthetic response to intercellular CO₂ concentration (A/C_i) and air CO₂ concentration (A/C_a), aiming to approach the reasonability of the fitted results obtained from the models.

Important findings The sequence of fitting effect of the three CO₂ response models in descending order was as follows: modified rectangular hyperbola model > rectangular hyperbola model > biochemical model. Fitted values of A/C_a curve was more reasonable than A/C_i curve, because the photorespiration and mitochondrial respiration under light (R_d) estimated by the former better matched the measured values. However, there were significant differences in the whole between the fitted and measured values. The reason could be that the effect of CO₂ concentrations on R_d and apparent photorespiration (R_pa) is neglected in all the current CO₂ response models. Our results showed that CO₂ concentration had a marked effect on R_pa and R_d. With increasing CO₂ concentration, R_pa and R_d increased first, and then decreased sharply. Take 2000 μmol·m^-2·s^-1 for example, R_pa varied between 5.035 and 11.670 μmol CO₂·m^-2·s^-1, and R_d varied between 0.491 and 2.987 μmol CO₂·m^-2·s^-1. Regression analyses indicated that R_pa and R_d were well related to CO₂ concentrations at different light intensities.