Tight coordination in the photosynthetic, gas exchange and water supply capacities of leaves is a globally conserved trend across land plants. Strong selective constraints on leaf carbon gain create the opportunity to use quantitative optimization theory to understand the connected evolution of leaf photosynthesis and water relations. We developed an analytical optimization model that maximizes the long-term rate of leaf carbon gain, given the carbon costs in building and maintaining stomata, leaf hydraulics and osmotic pressure. Our model demonstrates that selection for optimal gain should drive coordination between key photosynthetic, gas exchange and water relations traits. It also provides predictions of adaptation to drought and the relative costs of key leaf functional traits. Our results show that optimization in terms of carbon gain, given the carbon costs of physiological traits, successfully unites leaf photosynthesis and water relations and provides a quantitative framework to consider leaf functional evolution and adaptation.

叶片光合作用、气体交换和供水能力的紧密协调是全球陆地植物的保守趋势。对叶片碳增益的强选择性约束为使用定量优化理论来了解叶片光合作用和水分关系的相关演化提供了机会。考虑到建立和维护气孔、叶片水力学和渗透压的碳成本，我们开发了一个分析优化模型，可以最大限度地提高叶片碳增益的长期速率。我们的模型表明，最佳增益的选择应该推动关键光合作用、气体交换和水关系特征之间的协调。它还提供了对干旱适应和关键叶片功能性状的相对成本的预测。我们的结果表明，在碳增益方面的优化，