Geographic distribution of C₄ species and its phylogenetic structure across China

Over the past fifty years, the distribution patterns of C-4 species, across large spatial scales, are largely ignored. Here, we endeavored to examine patterns in the taxonomic and phylogenetic diversity of species with C-4 photosynthetic pathways across the broad spatial extent of China and relate those to climatic gradients. We built a database of all plants with the C-4 photosynthetic pathway in China. We analyzed the geographic distributions, taxonomic diversity, phylogenetic diversity, and phylogenetic structure of all C-4 species, as well as the three families with the most C-4 species (Poaceae, Amaranthaceae and Cyperaceae), and compared their values along temperature and precipitation gradients at two scales-the level of the province and at the 100 x 100 km grid cell. We found 644 C-4 plants (belonging to 23 families 165 genera) in China, with Poaceae (57%), Amaranthaceae (17%), Cyperaceae (13%) accounting for the majority of species. Standardized effect size values of phylogenetic distances were negative overall, indicating that C-4 species showed a phylogenetic clustering pattern. Southern China had the highest species richness and the highest degree of phylogenetic clustering. C-4 tended to be more phylogenetically over-dispersed in regions with colder and/or drier climates, but more clustered in warmer and/or wetter climates. Patterns within individual families were more nuanced. The distribution of C-4 species and its phylogenetic structure across China was constrained by temperature and precipitation. C-4 species showed a phylogenetic clustering pattern across China, while different families showed more nuanced responses to climate variation, suggesting a role for evolutionary history.