Relationship between gross primary productivity and plant species richness at geographical scales: evidence from protected area data in China

The large-scale relationship between gross primary productivity (GPP) and plant species richness (PSR) remains a fundamental topic in macro-ecology. Although there have been numerous studies of the connection between GPP and PSR, this relationship (linear or unimodal) is still debatable at geographical scales. Using geographically weighted regression and ordinary least squares, GPP and PSR data from protected areas in China were used to explore the complex relationship between GPP and PSR across different taxonomic groups (i.e. vascular plants, ferns, seed plants, gymnosperms, and angiosperms). Results showed that GPP was significantly related to PSR for all taxonomic groups at geographical scales (p<0.001). Such relationships varied among taxonomic groups. The explanatory power of GPP was highest for PSR in seed plants (58.5%; p<0.001). Further, the study found that the GPP-PSR relationships across different taxonomic groups at geographical scales were best described by a cubic regression, differing from the linear or unimodal relationships described thus far. Specifically, negative relationships were found between GPP and PSR at extremely low levels of GPP and GPP-PSR relationships were unimodal at relatively high GPP levels. This analysis provides new evidence regarding the relationship between GPP and PSR based on different taxonomic groups and develops the mechanisms and models of GPP linking to PSR at broad scales.