Classical approaches to estimate mesophyll conductance ignore differences in resistance components for CO2 from intercellular air spaces (IAS) and CO2 from photorespiration (F) and respiration (Rd). Consequently, mesophyll conductance apparently becomes sensitive to (photo)respiration relative to net photosynthesis, (F + Rd)/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 + Rd)/A ratios vary. This method was applied to tomato and rice leaves measured at five O2 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, CO2, and O2 levels, similar to response patterns of stomatal conductance to these variables. Largely due to different m values, the fraction of (photo)respired CO2 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 CO2 compensation point estimates, support our method of effectively analysing mesophyll resistance.

中文翻译：

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使用光呼吸氧气反应分析叶片的叶肉抗性。

估算叶肉电导的经典方法忽略了来自细胞间空域（IAS）的CO2和来自光呼吸（F）和呼吸（Rd）的CO2的抗性成分差异。因此，相对于净光合作用（F + Rd）/ A，叶肉电导显然对（光）呼吸敏感。这种敏感性取决于叶肉细胞的几种难以测量的解剖学特性。我们开发了一种方法来估计参数m（0≤m≤1），该参数会混淆（F + Rd）/ A比值的气体交换和叶绿素荧光测量，从而混淆了这些解剖特性。该方法适用于在五个O2水平下测量的番茄和水稻叶片。估计的m对番茄而言为0.3，对于大米而言为0.0，这表明暗示m = 0的经典方法对水稻有效。考虑到m因子的叶肉电导仍然对辐照度，CO2和O2水平有响应，类似于气孔电导对这些变量的响应模式。很大程度上由于m值的不同，番茄中（光）呼吸的CO2固定在叶肉细胞中的比例低于水稻。但这可以通过IAS的较高分数得到补偿，这使两个物种的总重新固定相似。这些结果与CO2补偿点估算值相符，支持我们有效分析叶肉抗性的方法。但这可以通过IAS的较高分数得到补偿，这使两个物种的总重新固定相似。这些结果与CO2补偿点估算值相符，支持我们有效分析叶肉抗性的方法。但这可以通过IAS的较高分数得到补偿，这使两个物种的总重新固定相似。这些结果与CO2补偿点估算值相符，支持我们有效分析叶肉抗性的方法。