Nitrogen and phosphorus constraints to photosynthetic capacity across different plant functional types

Nitrogen (N) and phosphorus (P) are considered the most significant limiting factors for plant growth in natural ecosystems. While Vcmax and Jmax can be predicted reasonably well based on N content, as included in some existing models, predictions improve when P content is taken into account. However, the evidence supporting the role of P in relation to Vcmax and Jmax mainly in tropical ecosystems and the relationship between leaf nutrient traits (both N and P) and photosynthetic parameters across global biomes and climate zones remains unclear due to a lack of data from temperate and boreal regions. In this study, we analyze observations from species across 21 plant functional types (PFTs), 7 biomes, and 4 climate zones, encompassing both broadleaf and needle-leaf temperate and boreal species, to investigate how these N and P influence photosynthetic parameters while considering the variations among different PFTs. The results show that the interaction between leaf nitrogen and phosphorus content significantly affects Vcmax for different plant functional types. Additionally, the explanatory power of N and P as individual variables varies among the different functional types. For most temperate and boreal PFTs, the relationship between Jmax and Vcmax is significantly influenced by the inclusion of N or P. Our analysis highlights the importance of differentiating the relationships between photosynthetic capacity and nutrients across various plant functional types, providing a quantitative framework for understanding the constraints of N and P on photosynthesis.