Trade-offs between diversity and stability mediated by positive cohesion in sediment microbiomes under algal blooms

Abstract

Eutrophication-driven algal blooms represent profound disturbances that restructure aquatic ecosystems. However, the mechanisms by which sediment microbial diversity and species interactions govern community stability during such events remain inadequately resolved. Here, we tracked a natural dinoflagellate bloom in Lake Erhai, a eutrophying plateau lake in southwestern China, to assess pre- and post-bloom changes in sediment microbial communities using 16S rRNA and ITS sequencing. Our analyses revealed that algal blooms significantly reduced sediment microbial α-diversity and decreased community heterogeneity. Concurrently, co-occurrence networks exhibited tightened connectivity, evidenced by shorter average path lengths, increased edge density, and a pronounced rise in positive cohesion. Crucially, we found that sampling sites with higher species diversity have lower compositional stability (quantified as resistance to taxon turnover), while that with strong positive cohesion have higher compositional stability. In contrast, functional stability (metabolic potential) showed no significant relationship with either diversity or cohesion, indicating distinct regulatory mechanisms for compositional versus functional stability. These findings demonstrate a clear trade-off between species diversity and cooperative interactions in shaping compositional stability under bloom-induced stress. This work establishes that positive species cohesion, rather than diversity alone, is a critical mediator of microbial community resistance in sediments facing eutrophication pressures. It advances our mechanistic understanding of stability dynamics in microbiomes and underscores the need to integrate interaction networks when predicting ecosystem responses to anthropogenic disturbances.