The maximum carboxylation rate (Vcmax) is a key parameter in determining the plant photosynthesis rate per unit leaf area. However, most terrestrial biosphere models currently treat Vcmax as constants changing only with plant functional types, leading to large uncertainties in modeled carbon fluxes. Vcmax is tightly linked with Ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco). Here we investigated the relationship between leaf chlorophyll and Rubisco (Chl‐Rub) contents within a winter wheat paddock. With chlorophyll as a proxy of Rubisco, a semimechanistic model was developed to model Vcmax₂₅ (Vcmax normalized to 25°C)_. The Chl‐Rub relationship was validated using measurements in a temperate mixed deciduous forest in Canada. The results showed that Rubisco was strongly correlated with chlorophyll (R ² = 0.96, p  < 0.001) for winter wheat since the absorption of light energy by chlorophyll and the amount of CO₂ catalyzed by Rubisco are tightly coupled. Incorporating the Chl‐Rub relationship into the semimechanistic model, the root mean square error of modeled Vcmax₂₅ was the lowest among all estimation models. The slopes of Chl‐Rub relations were almost consistent in the winter wheat and temperate forest, demonstrating the potential for using leaf chlorophyll content as a proxy of leaf Rubisco in modeling Vcmax₂₅ at large spatial scales. We anticipate that improving Vcmax₂₅ estimates over time and space will reduce uncertainties in global carbon budgets simulated by terrestrial biosphere models.

中文翻译：

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叶绿素含量作为Rubisco含量的代表的最大羧化速率估计

最大羧化速率（Vcmax）是确定每单位叶面积植物光合作用速率的关键参数。但是，目前大多数陆地生物圈模型都将Vcmax视为仅随植物功能类型而变化的常数，从而导致模拟碳通量存在较大不确定性。Vcmax与核糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）紧密相连。在这里，我们研究了冬小麦围场中叶绿素与Rubisco（Chl-Rub）含量之间的关系。以叶绿素为Rubisco的替代物，开发了一种半机械模型来模拟Vcmax ₂₅（Vcmax标准化为25°C）_。Chl-Rub关系已通过在加拿大温带混合落叶林中的测量得到验证。结果表明，Rubisco与 冬小麦的叶绿素高度相关（R ²  = 0.96，p <0.001），因为叶绿素吸收光能与Rubisco催化的CO ₂量紧密相关。将Chl-Rub关系纳入半力学模型中，建模的Vcmax _25的均方根误差在所有估计模型中最低。Chl-Rub关系的斜率在冬小麦和温带森林中几乎是一致的，这表明在建立Vcmax _25时可以利用叶绿素含量代替叶Rubisco。在大的空间尺度上。我们预计随着时间和空间的增长，Vcmax ₂₅估计值的提高将减少由陆地生物圈模型模拟的全球碳预算的不确定性。