Salinity-driven differentiation of bacterial and fungal communities in coastal wetlands: Contrasting assembly...

Coastal wetlands are critical for carbon sequestration and coastal protection, yet increasingly threatened by salinization. While soil microbiota mediate these ecosystems' functioning and stability, the mechanisms governing bacterial and fungal assembly across intermediate spatial scales remain poorly resolved. Here, we investigated microbial communities across a 30-km seaward-to-landward gradient in the Yellow River Delta during May 2020 using 16S rRNA and ITS sequencing coupled with ecological modeling. Our results revealed a striking dichotomy: bacterial communities were predominantly structured by deterministic environmental filtering (explained 49.2 % of variation), whereas fungal communities exhibited stronger spatial dependence (Mantel r = 0.28 vs 0.06 for bacteria, P < 0.01). Null model analyses confirmed salinity-driven variable selection for bacteria (60.0 % contribution) and stochastic homogenizing dispersal for fungi (44.9 %). Microbial interaction network analysis (based on taxon co-occurrence patterns) demonstrated the fungal network resisted salinity perturbations through high modularity (0.87 vs 0.68 for bacteria) and short path lengths (3.10 vs 4.90). Path analysis further showed geographic distance indirectly stabilized fungal networks (indirect effect = 0.33) but minimally affected bacteria. These findings highlight contrasting ecological strategies: bacteria prioritize deterministic variable selection for rapid resource acquisition, whereas fungi rely on homogenizing dispersal for spatial stability. These findings advance our understanding of microbial responses to salinization under climate change, informing adaptive management strategies to preserve microbial-mediated carbon storage and ecosystem functionality in salt-affected soils.