Untangling the influence of phylogeny, soil and climate on leaf element concentrations in a biodiversity hotspot

Plant elemental properties are fundamentally important for physiology and biogeochemical cycling in ecosystems. No study has examined foliar elements and their interaction with soil and climate conditions at large geographic scales in Karst areas of China, a biodiversity hotspot in the world. Yet such information is important for understanding the functional diversity of nutrient strategies and the physiological adaptations of plants to climatic and edaphic heterogeneity. We assessed the influence of phylogeny, soil type and the climate on leaf element concentrations in a clade of taxonomically diverse Karst plants from the subfamily Didymocarpoideae under an explicit phylogenetic framework. We measured leaf concentrations of seven elements and evaluated soil properties for 422 populations of 177 Didymocarpoideae species. The phylogenetic signals present in the leaf element concentrations and in soil and climatic variables were quantified at both the subfamily (Didymocarpoideae) and genus (Primulina) levels. The correlations between leaf elements and soil and climate conditions were analysed at these two phylogenetic scales. The Didymocarpoideae subfamily is generally characterized by higher Ca and Mg contents relative to other plants in China. Across the subfamily, a strong phylogenetic signal is detected for all of the leaf elements analysed as well as for most soil and climate variables, whereas the genus Primulina exhibits no significant phylogenetic signal in leaf elements or in most soil variables. We detected an influence of both soil and climatic conditions on leaf element concentrations. However, the patterns of the relationships between leaf elements and soil and climate variables vary at the subfamily and genus levels. The phylogeny has a stronger effect than soil and climatic factors on leaf element concentrations at the subfamily level, while the leaf element contents within the genus Primulina are mostly influenced by environmental conditions. We conclude that the influences of taxonomy, soil and climate on leaf element concentrations are dependent on the phylogenetic scale of analysis.