Gross primary production (GPP)-the uptake of carbon dioxide (CO₂) by leaves, and its conversion to sugars by photosynthesis-is the basis for life on land. Earth System Models (ESMs) incorporating the interactions of land ecosystems and climate are used to predict the future of the terrestrial sink for anthropogenic CO₂¹ . ESMs require accurate representation of GPP. However, current ESMs disagree on how GPP responds to environmental variations ^1,2 , suggesting a need for a more robust theoretical framework for modelling ^3,4 . Here, we focus on a key quantity for GPP, the ratio of leaf internal to external CO₂ (χ). χ is tightly regulated and depends on environmental conditions, but is represented empirically and incompletely in today's models. We show that a simple evolutionary optimality hypothesis ^5,6 predicts specific quantitative dependencies of χ on temperature, vapour pressure deficit and elevation; and that these same dependencies emerge from an independent analysis of empirical χ values, derived from a worldwide dataset of >3,500 leaf stable carbon isotope measurements. A single global equation embodying these relationships then unifies the empirical light-use efficiency model ⁷ with the standard model of C₃ photosynthesis ⁸ , and successfully predicts GPP measured at eddy-covariance flux sites. This success is notable given the equation's simplicity and broad applicability across biomes and plant functional types. It provides a theoretical underpinning for the analysis of plant functional coordination across species and emergent properties of ecosystems, and a potential basis for the reformulation of the controls of GPP in next-generation ESMs.

中文翻译：

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建立植物吸收二氧化碳的通用模型。

初级生产总值（GPP）-叶片吸收二氧化碳（CO ₂），以及通过光合作用将其转化为糖-是陆地生命的基础。地球系统模型（ESM）结合了土地生态系统和气候的相互作用，被用于预测人为源CO ₂ ¹的地面汇的未来。ESM需要GPP的准确表示。但是，当前的ESM在GPP如何响应环境变化^1,2上存在分歧，这表明需要用于模型^3,4的更强大的理论框架。在此，我们重点关注GPP的关键数量，即叶片内部与外部CO ₂的比率（χ）。χ受严格监管，并取决于环境条件，但在今天的模型中经验和不完整地表示。我们证明了一个简单的进化最优性假设^5,6可以预测χ对温度，蒸气压赤字和海拔的特定定量依赖性；而且这些相同的依赖性来自对经验χ值的独立分析，这些经验χ值来自于全球3500多个叶片稳定碳同位素测量数据集。体现这些关系的单个全局方程式将经验光利用效率模型⁷与C ₃光合作用的标准模型⁸统一起来。，并成功预测在涡度-协方差通量站点测得的GPP。鉴于该方程式的简单性以及在生物群落和植物功能类型中的广泛适用性，因此这一成功非常显着。它为分析跨物种的植物功能协调和生态系统的新特性提供了理论基础，并为在下一代ESM中重新设计GPP控件提供了潜在的基础。