Continental-scale β diversity of bacteria and fungi vary differentially with soil pH in forests

Abstract:  The soil microbiota is crucial for regulating biogeochemical cycles, including soil carbon (C) dynamics and nutrient cycling. However, how climate, plants, and soil properties influence the microbiome in forests at a continental scale remains unclear, hampering us from better understanding forest C-climate change feedback. Here, we investigated the spatial patterns of microbial diversity across China’s forests and explored the factors controlling microbial β diversity and network complexity. Our results showed that bacterial and fungal β diversity were strongly influenced by soil pH and climate. To further investigate the environmental preference of the microbial networks, we classified the zero-radius operational taxonomic units (zOTUs) into five groups ranging from acidic to alkaline soils. Co-occurrence network analysis revealed that the topological structure of the bacterial network (e.g., edge and degree) increased with pH and had a negative relationship with β diversity but not with fungal diversity. Soil fungi exhibit greater β diversity with network complexity (i.e., degree and betweenness) than bacteria at pH < 5.1 and vice versa in neutral and alkaline soils (pH > 5.5). Within the pH range of 5.1-5.5, the bacteria-fungi network exhibited the most increased network complexity but the lowest fungal β diversity, with significant positive correlations found between fungal β diversity and soil properties. Furthermore, 46 bacterial core species were identified and shown to be significantly correlated with soil pH. These findings highlight the critical role of soil pH in driving soil microbial β diversity across China’s forests and reveal the effects of pH thresholds on changes in the soil microbial network and core species.

Keywords: Bacterial diversity, fungal diversity, network analysis, forest