Exploring the Feasibility of Global Mapping of the Leaf Carboxylation Rate

Photosynthesis in vegetation is arguably the most important and variable part of the terrestrial carbon cycle. In terrestrial biospheric models, the photosynthesis rate of plant leaves is generally simulated based on the maximum carboxylation rate at an optimum temperature (often 25°C), which is often denoted as Vcmax25. In regional and global photosynthesis modeling, Vcmax25 is usually prescribed as constants for different plant functional types (PDF) based on ground measurements in order to capture the first order spatial variability associated with PTF distribution. However, experimental data show that Vcmax25 can vary by 2-3 factors for the same PFT, and it is also not a constant in different growing seasons because of leaf physiological change with season. It is therefore highly desirable to be able to map this critical parameter to address the issues of its spatial and temporal variabilities. Both terrestrial carbon and water cycle simulations can be greatly improved if we can achieve the global mapping of this parameter.