Where in the leaf is intercellular CO2 (Ci)? Considerations and recommendations for assessing gaseous diffusion in leaves
Where in the leaf is intercellular CO2 (Ci)? Considerations and recommendations for assessing gaseous diffusion in leaves
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细胞间 CO2 (Ci) 位于叶子的什么位置？
DOI：
10.1101/2020.05.05.079053
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Hanson David T.
中科院分区：
文献类型：
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作者：
Stinziano Joseph R.;Tominaga Jun;Hanson David T.
水汽交换完全通过气孔进行，细胞间空间完全被水汽饱和，气孔与细胞间空间之间的CO2梯度可以忽略不计，这些假设使得近60年来通过计算细胞间CO2（Ci）在光合气体交换研究中取得了重大进展。然而，现有证据表明，这些假设可能被过度使用了。在这里，我们回顾了支持和反对莫斯和罗林斯（1963）所作假设的文献。我们通过传播不同的角质层失水速率、二氧化碳梯度和不饱和度来重新解释文献中的数据。我们发现，一般情况下，当角质层导度小于气孔导度的1%时，水汽交换完全通过气孔进行的假设对气体交换计算有边际影响，但当角质层导度超过气孔导度的5%时，则不成立。在高气孔导度条件下，co2和水汽梯度的影响更大，而角质层导度的影响更大。因此，我们建议在可能的情况下直接测量水分，测量外质体水势来估计叶片内部的湿度，并且在高温和/或低气孔导度的条件下解释数据时要谨慎，当一个物种已知具有高角质层导度时。叶片水蒸气和co2交换已经成功地用于模拟光合生物化学。我们回顾了这些模型中的关键假设，并提出了需要重新评估的建议。
The assumptions that water vapor exchange occurs exclusively through stomata, that the intercellular airspace is fully saturated with water vapor, and that CO2gradients are negligible between stomata and the intercellular airspace have enabled significant advancements in photosynthetic gas exchange research for nearly 60 years via calculation of intercellular CO2(Ci). However, available evidence suggests that these assumptions may be overused. Here we review the literature surrounding evidence for and against the assumptions made by Moss & Rawlins (1963). We reinterpret data from the literature by propagating different rates of cuticular water loss, CO2gradients, and unsaturation through the data. We find that in general, when cuticle conductance is less than 1% of stomatal conductance, the assumption that water vapor exchange occurs exclusively through stomata has a marginal effect on gas exchange calculations, but this is not true when cuticle conductance exceeds 5% of stomatal conductance. Our analyses further suggest that CO2and water vapor gradients have stronger impacts at higher stomatal conductance, while cuticle conductance has a greater impact at lower stomatal conductance. Therefore, we recommend directly measuring Ciwhenever possible, measuring apoplastic water potentials to estimate humidity inside the leaf, and exercising caution when interpreting data under conditions of high temperature and/or low stomatal conductance, and when a species is known to have high cuticular conductance.HighlightLeaf water vapor and CO2exchange have been successfully used to model photosynthetic biochemistry. We review critical assumptions in these models and make recommendations about which need to be re-assessed.