Thermal discharge exerts limited effects on sediment prokaryotic community compositions but markedly enhances...

Thermal discharge from power plants locally elevates seawater temperatures, profoundly affecting marine ecosystems. While its impacts on aquatic prokaryotic communities are well documented, sediment prokaryotic responses remain poorly understood. Here we combined amplicon sequencing and metatranscriptomics to investigate sediment prokaryotic responses to thermal discharge. Sediment temperatures increased by 1.0-2.22 °C. Under this moderate warming, community composition remained largely stable, with only Nitrosopumilaceae showing significant temperature-responsive changes. In contrast, functional profiles shifted markedly, with oxidative phosphorylation (OXPHOS) and phosphorus metabolism pathways significantly upregulated. Key genes in respiratory complexes including NADH dehydrogenase, succinate dehydrogenase, cytochrome bc1 and oxidase, and ATP synthase, as well as regulatory enzymes ppa and ppk, were upregulated, while activation of the pentose phosphate pathway (PPP) supplied nucleotides and NADPH to support biosynthesis and mitigate oxidative stress. The concurrent upregulation of PPP and OXPHOS indicates a coordinated metabolic strategy to meet higher energy demands while maintaining redox homeostasis. These findings reveal a decoupling between taxonomic composition and functional activity, showing that sediment prokaryotic communities, although compositionally resilient, are functionally sensitive to thermal perturbation. This adaptive functional response has important implications for nutrient cycling and sediment ecosystem stability under continuous thermal discharge.