Centre for Crop Systems Analysis, Wageningen University & Research, P.O. Box 430, 6700 AK, Wageningen, The Netherlands.
Selale University, P.O. Box 245, Fiche, Ethiopia.
Photosynth Res. 2020 Apr;144(1):85-99. doi: 10.1007/s11120-020-00716-z. Epub 2020 Feb 10.
Classical approaches to estimate mesophyll conductance ignore differences in resistance components for CO from intercellular air spaces (IAS) and CO from photorespiration (F) and respiration (R). Consequently, mesophyll conductance apparently becomes sensitive to (photo)respiration relative to net photosynthesis, (F + R)/A. This sensitivity depends on several hard-to-measure anatomical properties of mesophyll cells. We developed a method to estimate the parameter m (0 ≤ m ≤ 1) that lumps these anatomical properties, using gas exchange and chlorophyll fluorescence measurements where (F + R)/A ratios vary. This method was applied to tomato and rice leaves measured at five O levels. The estimated m was 0.3 for tomato but 0.0 for rice, suggesting that classical approaches implying m = 0 work well for rice. The mesophyll conductance taking the m factor into account still responded to irradiance, CO, and O levels, similar to response patterns of stomatal conductance to these variables. Largely due to different m values, the fraction of (photo)respired CO being refixed within mesophyll cells was lower in tomato than in rice. But that was compensated for by the higher fraction via IAS, making the total re-fixation similar for both species. These results, agreeing with CO compensation point estimates, support our method of effectively analysing mesophyll resistance.
经典方法估算胞间 CO2 导度时忽略了 CO2 从胞间空间（IAS）扩散和从光呼吸（F）及呼吸（R）扩散的阻力组分的差异。因此，胞间 CO2 导度对净光合速率（F+R）/A 的相对光呼吸（F）变得敏感。这种敏感性取决于难以测量的几个叶肉细胞解剖学特性。我们开发了一种方法，使用气体交换和叶绿素荧光测量来估算参数 m（0≤m≤1），该参数综合了这些解剖学特性，其中（F+R）/A 比值变化。该方法应用于在五个 O 水平下测量的番茄和水稻叶片。估算的 m 值为 0.3 对于番茄，但对于水稻为 0.0，这表明对于水稻，经典方法假设 m=0 是可行的。考虑 m 因子的胞间 CO2 导度仍然对光照、CO2 和 O 水平做出响应，与气孔导度对这些变量的响应模式相似。主要由于不同的 m 值，在番茄中，光呼吸 CO2 的被固定在叶肉细胞内的分数比在水稻中低。但是，通过 IAS 的分数更高，从而使两种物种的总固定分数相似。这些结果与 CO2 补偿点的估计值一致，支持我们有效分析胞间阻力的方法。
