A global database of photosynthesis model parameters, and modelled photosynthetic responses from every major terrestrial plant clade

Abstract

Plant photosynthesis is a major part of the global carbon cycle and climate system. Carbon capture by C3 plants is most often modelled using the Farquhar-von-Caemmerer-Berry (FvCB) equations. We undertook a global synthesis of all parameters required to solve the FvCB model. The publicly available dataset we assembled includes 3663 observations from 359 different plant species among 96 taxonomic families coming from every major vascular plant clade (lycophytes, ferns, gymnosperms, magnoliids, eudicots and monocots). Geographically, the species in the database have distributions that span the majority of the globe. We used the model to predict photosynthetic rates for the average plant in each major terrestrial plant clade and find that generally plants have dramatically increased their photosynthetic abilities through evolutionary time, with the average monocot (the youngest clade) achieving maximum rates of photosynthesis almost double that of the average lycophyte (the oldest clade). However, there was no evidence of niche conservatism with most variance occurring within, rather than among clades (K=0.357, p=0.001). We also solved the model for different average plant functional types (PFTs) and find that herbaceous species generally have much higher rates of photosynthesis compared to woody plants. Indeed, the maximum photosynthetic rate of graminoids is almost three times the rate of the average tree. The resulting functional responses to increasing CO2 suggest that most groups are already at or near their maximum rate of photosynthesis. Unfortunately, only graminoids seem to have the capacity to continue to increase photosynthetic rates with increasing CO2 concentrations in the atmosphere. We view this as version 1.0 of a database for global photosynthesis parameters and functional responses and hope that the publicly available dataset can improve models of photosynthesis.