Fungi and bacteria in the rhizosphere of Cryptomeria japonica exhibited different community assembly patterns at regional scales in East Asia

Rhizosphere microbes are key components of soil biodiversity involved in forest ecosystem functions. However, the patterns of community structure and community assembly for different domains of microbes (i.e., fungi and bacteria) remains poorly understood at broad spatial scales. We examined community structure of rhizosphere fungi and bacteria in eight Cryptomeria japonica plantations distributed from cool temperate to subtropical zones in Japan and Taiwan. Beta diversity of fungal and bacterial communities significantly related to environmental (soil pH, C/N ratio or electrical conductivity) and spatial factors, but the fungal and bacterial communities were assembled by different ecological processes. Null model analysis showed that drift (34.4%) and dispersal limitation (48.9%) were the dominant drivers shaping fungal communities, and homogeneous selection (72.1%) were dominant in bacterial communities, indicating that stochasticity and determinism dominate community assembly of fungi and bacteria, respectively. Co-occurrence network analyses targeting frequently detected microbial taxa indicated that significant relationships were detected mostly between bacterial taxa (381/438) followed by between fungal and bacterial taxa (55/438). Putative biological interactions (40.2% and 75.0% between bacterial taxa and between fungal and bacterial taxa, respectively) and environmental filtering (33.6%–57.6%, 16.7%–20.9%) contributed highly to the co-present relationships of taxon pairs, and environmental filtering (55.3%–86.2%, 35.5%–71.0%) contributed highly to the mutually exclusive relationships of taxon pairs, indicating that not only environmental factors but also biotic interaction are important processes in aggregation among fungal and bacterial taxa. It was suggested that fungi are more influenced by stochastic processes than biotic and abiotic environmental filtering, whereas bacteria are more influenced by biotic interactions and abiotic factors such as soil properties and climate than stochastic processes at the regional scale. The results of this study provide a comprehensive view of microbial dynamics surrounding woody fine roots that can be useful for predicting the response of forest ecosystems to local and global environmental changes in East Asian cedar plantations.