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<p>Small coastal rivers form compressed river–estuary–offshore continua that regulate biogeochemical cycling yet remain underexplored. Here we show that gradient compression is a pivotal control on sediment microbial community turnover. Using full-length 16S and ITS sequencing, we found that bacterial assembly is predominantly deterministic (&gt; 50%), whereas fungal assembly is largely stochastic (&gt; 66%). This divergence yields contrasting spatial outcomes: estuaries emerge as bacterial network hotspots but fungal dilution zones, while offshore selective pressure promotes functional specialisation and reduced predicted redundancy. Together, these patterns suggest ecosystems that are structurally complex yet potentially functionally vulnerable. By integrating community structure, assembly processes, and functional profiles with environmental gradients, our study proposes a mechanism by which steep gradients can erode functional redundancy and, potentially, resilience. We further show that such small-scale systems—ubiquitous worldwide—may be especially sensitive to perturbations, underscoring the need for early-warning indicators within watershed risk management.</p><p></p>

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Gradient compression drives divergent sediment bacterial and fungal assembly from river to sea

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2026年4月20日

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  • Jingyi Xu,
  • Kaichao Wan,
  • Dianwei Zhang,
  • Kaiqi Zhang,
  • Yanbin Fan,
  • Qiang Fu,
  • Weidong Wang

摘要

Small coastal rivers form compressed river–estuary–offshore continua that regulate biogeochemical cycling yet remain underexplored. Here we show that gradient compression is a pivotal control on sediment microbial community turnover. Using full-length 16S and ITS sequencing, we found that bacterial assembly is predominantly deterministic (> 50%), whereas fungal assembly is largely stochastic (> 66%). This divergence yields contrasting spatial outcomes: estuaries emerge as bacterial network hotspots but fungal dilution zones, while offshore selective pressure promotes functional specialisation and reduced predicted redundancy. Together, these patterns suggest ecosystems that are structurally complex yet potentially functionally vulnerable. By integrating community structure, assembly processes, and functional profiles with environmental gradients, our study proposes a mechanism by which steep gradients can erode functional redundancy and, potentially, resilience. We further show that such small-scale systems—ubiquitous worldwide—may be especially sensitive to perturbations, underscoring the need for early-warning indicators within watershed risk management.