Temperature modulates sediment priming triggered by simulated algal blooms: Insights from sediment microbial fuel cells

Abstract. Mangrove sediments are major blue carbon reservoirs, yet how warming and eutrophication interact to control the stability of sediment organic carbon (SOC) remains uncertain. Here, we combined sediment microbial fuel cell (SMFC) monitoring with (in)organic carbon analyses, and lignin biomarker measurements in ¹³C-labeled algal-amended subtropical mangrove sediments to investigate temperature-dependent priming of SOC at 25, 30, and 35 ℃. Baseline SOC mineralization exhibited a nonlinear increase across the 25–30 °C thermal range, followed by a distinct decline at 35 °C. In contrast, priming intensity increased progressively with increasing temperature, shifting from weakly negative to strongly positive. This divergence reveals that warming decouples intrinsic SOC mineralization from priming-driven carbon turnover. Mechanistically, algal inputs provided energetic sources that activated opportunistic copiotrophs (Bacteroidota) and restructured anodic interactomes by enriching syntrophic microorganisms (e.g., Anaerolineaceae, Desulfosarcinaceae). Rather than relying on obligate aerobes, late-stage oxidative cleavage of recalcitrant lignin phenols was sustained under anoxic conditions by the active anode, which served as an inexhaustible electron sink via extracellular electron transfer. These findings suggest that warming shifts microbial metabolisms rather than uniformly stimulating carbon mineralization, promoting the priming degradation of otherwise stable SOC. Consequently, warming may disproportionately increase the vulnerability of stabilized SOC in eutrophic mangrove ecosystems by amplifying priming effects relative to baseline mineralization. Incorporating temperature-dependent priming into blue carbon models may improve predictions of coastal carbon storage under future climate change.