Graduate School of Integrated Sciences for Life, Hiroshima University, Hiroshima 739-8528, Japan.
Faculty of Agriculture, University of the Ryukyus, Okinawa 903-0213, Japan.
J Exp Bot. 2024 May 20;75(10):2982-2993. doi: 10.1093/jxb/erae081.
Leaf gas-exchange measurements are useful in assessing plant environmental responses. However, uncertainties in the leaf gas-exchange model potentially limit its application. The main challenge in the model-dependent calculations is to detect violations of assumptions. Here, we developed a system that integrates into one instrument the direct measurement of leaf intercellular CO2 concentration and the standard open-flow (OF) and novel open-diffusion (OD) systems for flux measurement. In the OD system, a gas-permeable membrane between the leaf ambient air and outside air creates CO2 and H2O differentials, rather than the air flow in the OF chamber. We measured hypostomatous and amphistomatous leaves of several species with different photosynthetic capacities [sunflower (Helianthus annuus), grape (Vitis vinifera), lemon (Citrus limon), and cherry (Prunus avium)]. The CO2 and H2O differentials in the OD system strictly depend on the flux measured by the OF system. The lower permeability of the membrane resulted in a larger differential per flux, indicating that the OD system can increase the resolution for a small flux. An analysis of the conductance model along with observations suggested that cuticle and leaf intercellular conductances and the unsaturation of leaf humidity contributed to discrepancies between the direct measurement and standard calculation. The combined system developed here provides an opportunity to address these overlooked concepts in leaf gas exchange.
叶片气体交换测量在评估植物环境响应方面非常有用。然而，叶片气体交换模型中的不确定性可能限制了其应用。在基于模型的计算中，主要的挑战是检测假设的违反。在这里，我们开发了一个系统，将叶片胞间 CO2 浓度的直接测量与标准开路（OF）和新型开路扩散（OD）通量测量系统集成到一个仪器中。在 OD 系统中，叶片环境空气和外部空气之间的透气膜会产生 CO2 和 H2O 的差异，而不是 OF 室中的气流。我们测量了几种具有不同光合能力的叶片（向日葵（Helianthus annuus）、葡萄（Vitis vinifera）、柠檬（Citrus limon）和樱桃（Prunus avium））的下表皮和上表皮叶片。OD 系统中的 CO2 和 H2O 差异严格取决于 OF 系统测量的通量。膜的较低渗透率导致每通量的差异更大，这表明 OD 系统可以提高小通量的分辨率。对导纳模型的分析以及观察结果表明，角质层和叶片胞间导纳以及叶片湿度的不饱和导致了直接测量和标准计算之间的差异。这里开发的组合系统为解决叶片气体交换中这些被忽视的概念提供了机会。
