Different factors drive community assembly of rare and common ectomycorrhizal fungi

1.Understanding what drives community assembly processes and how communities respond to environmental gradients are fundamental goals in community ecology. Ectomycorrhizal fungi support major forest systems across the globe, but the diversity, distribution and environmental controls affecting ectomycorrhizal community composition are unknown in many regions, particularly in the southern hemisphere. Here we investigate the assembly of ectomycorrhizal fungal communities based on eDNA samples from 81 Nothofagus forests across New Zealands South Island. We apply zeta diversity analysis and multi-site generalised dissimilarity modelling (MS-GDM) to investigate assembly patterns and quantify the effects of 43 biotic and environmental variables on community turnover. The zeta diversity MS-GDM framework differentiates between the environmental factors driving turnover of rare and common species, so provides a more complete picture of community dynamics than traditional beta diversity analyses. Results showed that community assembly was dominated by deterministic rather than stochastic processes. Soil variables were important drivers across the full range of rare, intermediate and common species. Ground cover variables, forest patch size and rainfall had greater effects on turnover of rare species, whereas temperature variables and host tree size had greater effects on common species turnover. Applying these methods for the first time to fungi demonstrates that there are distinct differences in the ecological processes affecting different aspects of the ectomycorrhizal community, which has important implications for understanding the functional effects of community responses to environmental change.