Seasonal patterns in diversity, complexity and community assembly of soil microorganisms in a subtropical coastal wetland

Soil microbiomes are significant for biodiversity, crucial for ecosystem functions, and vital for the health of various organisms. Nevertheless, the impacts of season and plant species shifts on soil microbial diversity and community assembly are still poorly understood. This study explored soil bacterial, fungal, and protistan communities during summer and winter in a coastal wetland affected by Spartina alterniflora invasion and subsequent Cyperus malaccensis or Kandelia obovata restoration. The results showed that bacterial, fungal, and protistan diversity were 2.63%, 40.3%, and 9.90% higher in winter than in summer, respectively. Plant species had a distinct impact on microbial diversity. Notably, K. obovata restoration significantly increased bacterial diversity, but decreased protistan diversity, with no effect on fungal diversity when compared to S. alterniflora invasion. Season and plant species both significantly influenced the community structure of bacteria, fungi, and protists. However, protistan community structure was more sensitive to season compared to the structure of bacterial and fungal communities. The complexity of co-occurrence networks within or among bacteria, fungi, and protists was higher in winter than in summer. Bacterial and protistan community assembly was primarily driven by stochastic processes, while fungal assembly was dominated by deterministic processes. Bacterial and protistan community assembly exhibited lower stochasticity in winter compared to summer, suggesting a more deterministic assembly of communities during winter. Our findings highlight the critical role of season and plant species in regulating microbial communities, revealing higher microbial diversity, network complexity, and determinism in community assembly during winter compared to summer in a subtropical coastal wetland.