以C₃作物(小麦, Triticum aestivum和大豆, Glycine max)和C₄作物(玉米, Zea mays和千穗谷, Amaranthus hypochondriacus)为例, 探讨了其光下暗呼吸速率降低的原因。结果表明, 2% O₂条件下, CO₂浓度为0时, 叶室CO₂浓度维持在0左右, 而胞间CO₂浓度(C_i)显著高于叶室CO₂浓度。分析认为这是由于此时植物的暗呼吸仍在正常进行。因此, 该测量条件下的表观光合速率应为CO₂浓度为0时的光下暗呼吸速率(R_d)。CO₂浓度为0时, 不同光强下的R_d均随光强的升高而降低, 且在低光强(50 μmol·m^-2·s^-1)和高光强(2000 μmol·m^-2·s^-1)之间存在显著差异, 说明光强对R_d具有较大影响。在2% O₂条件下, 经饱和光强充分活化而断光后, 以上4种作物叶片的暗呼吸速率(R_n)均随着时间的推移而下降, 说明光强并未抑制暗呼吸速率。试验结果表明, R_d的降低是由于CO₂被重新回收利用所导致, CO₂回收利用率随光强的升高而增大, 从低光强(50 μmol·m^-2·s^-1)到高光强(2000 μmol·m^-2·s^-1), 小麦、大豆、玉米和千穗谷的回收利用率范围变动分别为22.65%-52.91%、22.40%-55.31%、54.24%-87.59%和72.43%-90.07%。

Aims Despite the increasing attention given to the rate of mitochondrial respiration under light (R_d), considerable confusion persists over whether mitochondrial respiration in the dark (R_n) is inhibited by light and whether R_d is affected by light intensity. The objective of this study is to test the hypotheses: 1)R_n is not inhibited by light; 2) the rate of R_d changes with light intensity; and 3) the photosynthetic refixation of CO₂ produced by R_n accounts for the apparent disparity between R_d and R_n.
Methods In the present study, 0.02 mol·mol^-1 O₂ (i.e. 2% O₂) was used to saturate R_n and to inhibit photorespiration (R_p). By using combined gas exchange measurements and a low O₂ (2% O₂) method, the post-illumination CO₂ release rate of R_n, photosynthetic rate (P_n) in response to photosynthetically active radiation (PAR) in 2% O₂ at either 380 or 0 μmol·mol^-1 CO₂, of C₃ (Triticum aestivum and Glycine max) and C₄(Zea mays and Amaranthus hypochondriacus) plants, were measured.
Important finding R_n was not inhibited by light. At 2% O₂ and 0 μmol·mol^-1 CO₂, the measured parameters could be used to accurately estimate R_d when CO₂ concentration was set for 0 μmol·mol^-1. R_d decreased with increasing light intensity. Although R_d was lower in the dark, this could be accounted for by photosynthetic re-fixing of respiratory CO₂. For all plants tested, CO₂recovery rates increased with increasing light intensity (from 50 and 2 000 μmol·m^-2·s^-1).