The interactions between climate and soil factors influence the taxonomic and phylogenetic diversity of woody plants in the subtropical karst region

The woody plants in subtropical forests are one of the most important long-term carbon sinks in the terrestrial ecosystems. However, its diversity patterns and the underlying mechanisms remain unclear. To explore the diversity patterns of woody plants in subtropical forests, based on the census data of 180 forest-dynamics monitoring plots in Guizhou province, this study assessed the effects of climate and soil factors, and their interactions on taxonomic and phylogenetic diversity using the negative binomial regression model. The results indicated that both climate and soil factors substantially improved the model’s prediction accuracy (model d). When interactions between climate and soil factors were further considered, explanatory power increased by 45.49% for taxonomic diversity ( R 2 = 0.774) and by 26.62% for phylogenetic diversity ( R 2 = 0.742) compared with the case without interactions. In particular, although soil factors such as total potassium (TK) had relatively weak direct effects, their interactions with climatic variables ( e.g. , precipitation of the wettest month, Bio13) exerted substantially stronger influences. These interactions indicate that soil nutrient availability modulates plant responses to climatic variability, especially under conditions of fluctuating water supply. This may be attributed to the role of potassium in regulating stomatal function and enhancing plant responses to water availability under variable precipitation conditions. This study emphasizes the importance of environmental factors and their interactions in diversity patterns and community assembly of subtropical forests, which can provide empirical support for a deeper understanding of subtropical forest diversity patterns and assembly mechanisms.