Abstract The leaf maximum carboxylation rate ( V cmax ) is a crucial parameter in determining the photosynthetic capacity of plants. Providing accurate estimates of leaf V cmax , that cover large geographic areas and incorporate plant seasonality is central to correctly predicting carbon fluxes within the terrestrial global carbon cycle. Chlorophyll, as the main photon‐harvesting molecule in leaves, is closely linked to plant photosynthesis. However, how the nature of the relationship between the leaf maximum carboxylation rate (scaled to 25°C; V cmax,25 ) and leaf chlorophyll content varies according to plant type is uncertain. In this study, we investigate whether a universal and stable relationship exists between leaf V cmax,25 and leaf chlorophyll content across different plant types and verify it using field experiments. Measurements of leaf chlorophyll content (Chl) and CO 2 response curves were made on 283 crop, shrub, tree, and vegetable leaves, across 13 species, in China and southern Ontario, Canada. A strong relationship was found between the leaf V cmax,25 and chlorophyll content across different plant types ( R 2 = 0.65, p < 0.001). Cross‐validation showed that the model performs well, producing an RMSE value of 15.4 μmol m −2 s −1 . The results confirm that leaf chlorophyll content can be a reliable proxy for estimating V cmax,25 , opening the door to accurate, spatially continuous estimates of V cmax,25 at the global scale.
Plain Language Summary The leaf maximum carboxylation rate ( V cmax ) is a key photosynthesis parameter. Previous research has explored the relationships between leaf V cmax,25 and chlorophyll content or indicators associated with leaf chlorophyll content for many species. However, it remains unknown whether the relationship between leaf V cmax,25 and chlorophyll content across different plant types is uniform. This study attempts to explore the relationship between leaf V cmax,25 and chlorophyll content and verify it using field experiments. A linear empirical model was built to retrieve leaf V cmax,25 from chlorophyll content. This can provide an operational approach for remote sensing of retrieving leaf V cmax,25 based on the relationship between leaf V cmax,25 and chlorophyll content.
Key Points Similar seasonal variations in leaf chlorophyll content and in V cmax,25 were found for crops and forests using in situ observations The J max to V cmax relationship preserved across species/PFTs consolidates the chlorophyll‐based V cmax,25 method Leaf chlorophyll content can provide a reliable estimate of V cmax,25