• Photosynthetic capacity per unit irradiance is greater, and the marginal carbon revenue of water (∂A/∂E) is smaller, in shaded leaves than sunlit leaves, apparently contradicting optimization theory. I tested the hypothesis that these patterns arise from optimal carbon partitioning subject to biophysical constraints on leaf water potential.
• In a whole plant model with two canopy modules, I adjusted carbon partitioning, nitrogen partitioning and leaf water potential to maximize carbon profit or canopy photosynthesis, and recorded how gas exchange parameters compared between shaded and sunlit modules in the optimum.
• The model predicted that photosynthetic capacity per unit irradiance should be larger, and ∂A/∂E smaller, in shaded modules compared to sunlit modules. This was attributable partly to radiation‐driven differences in evaporative demand, and partly to differences in hydraulic conductance arising from the need to balance marginal returns on stem carbon investment between modules. The model verified, however, that invariance in the marginal carbon revenue of N (∂A/∂N) is in fact optimal.
• The Cowan–Farquhar optimality solution (invariance of ∂A/∂E) does not apply to spatial variation within a canopy. The resulting variation in carbon–water economy explains differences in capacity per unit irradiance, reconciling optimization theory with observations.

中文翻译：

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最佳碳分配有助于调和光合能力的最佳冠层和观察冠层之间的表观差异

• 每单位辐照光合能力更大，并且水的边际收益碳（∂甲/∂ ë）较小时，在阴影叶比阳光照射的叶，显然与优化理论。我测试了以下假设：这些模式是由最佳碳分配产生的，而碳分配受到叶水势的生物物理约束。
• 在具有两个冠层模块的整个植物模型中，我调整了碳分配，氮分配和叶水势，以最大化碳利润或冠层的光合作用，并记录了如何在最佳状态下比较阴凉和阳光照射的模块之间的气体交换参数。
• 该模型预测，每单位辐照光合能力应该更大，和∂甲/∂ é小，在阴影模块相比阳光照射的模块。这部分归因于辐射驱动的蒸发需求差异，部分归因于需要平衡模块之间干碳投资的边际收益而产生的水力传导率差异。模型验证，然而，不变性在N边际收益碳（∂甲/∂ Ñ）实际上是最佳的。
• 在Cowan的-夸尔最优溶液（∂的不变性甲/∂ ë）不篷内，向空间变化。碳水经济性的最终变化解释了单位辐照度容量的差异，从而使优化理论与观察结果相吻合。