Asymmetric microbial community reassembly under 7-year experimental precipitation decouples soil carbon storage in a coastal wetland

Climate-driven extremes in precipitation are fundamentally altering the hydrological regimes of wetland ecosystems. However, the mechanistic understanding of how soil microbial communities and their metabolic functions respond to precipitation change, and how these responses regulate soil organic carbon (SOC) dynamic, remains limited. Here, we leveraged a 7-year precipitation manipulation experiment (± 40%) in a coastal wetland and applied genome-resolved metagenomics to systematically examine microbial community structure, ecological networks, and key biogeochemical functions (carbon fixation and degradation). We found that although microbial community structure showed no pronounced response to increased precipitation, decreased precipitation reorganized the community, as evidenced by higher β-diversity and more complex co-occurrence networks with strengthened positive interactions. Compared with dominant species, rare species played a more important role in maintaining the stability of microbial networks. Functional potential for carbon degradation and fixation remained relatively stable under decreased precipitation. In contrast, increased precipitation concurrently suppressed degradation of polysaccharides and aromatic compounds, and some carbon fixation pathways, such as Acetyl-CoA (rAcCoA) pathway. Collectively, decreased and increased precipitation induced asymmetric responses in microbial communities, with decreased precipitation primarily reshaping community composition but having little effect on functional potential, whereas increased precipitation predominantly altered functional profiles without substantially changing community structure. We further found microbial community reassembly decoupled SOC content. Together, this study highlights that prolonged precipitation extremes shape coastal wetland microbiomes through divergent ecological trajectories; however, these microbial shifts may not necessarily translate directly into changes in soil carbon storage.