Bacterial necromass-derived organic matter triggers greenhouse gas production and priming effect in saline lake sediments

Bacterial necromass-derived OM constitutes a globally significant yet understudied reservoir of organic carbon and nitrogen, whose degradation dynamics in climate-sensitive saline lakes remain unresolved. This study quantifies how bacterially derived organic matter (OM) regulates CO2 and N2O production and priming effects (PE) across a natural salinity gradient (0.9–247.0 g L−1) in 20 lake sediments. Through microcosm experiments with 13C/15N-labelled Sphingomonas sp. necromass, we demonstrate that OM addition significantly enhances CO2 and N2O production rates (up to 104.73 μg C g−1 day−1 and 1,806.17 ng N g−1 day−1, respectively;p < 0.001), concurrent with increased abundances of 16S rRNA and functional genes (archaeal amoA, nirK, nosZ I). Positive priming effects (PE) dominates (−12.56 to 8.47 μg C-CO2 g−1 day−1), driven by upregulated prokaryotic taxa (Bacteroidetes, Firmicutes, and Proteobacteria) that preferentially decompose plant-derived organic molecules (e.g., lignin- and tannin-like compounds. Archaeal ammonia oxidation andnirK-denitrification fueled by labile OM substrates are identified as key N2O production pathways, with salinity suppressing CO2 fluxes but not N2O emissions. FT-ICR-MS reveals molecular shifts in dissolved OM (increased CHONS/condensed aromatics; decreased CHO/lignins) linked to microbial community restructuring. These findings establish bacterial necromass-derived OM as a critical regulator of carbon and nitrogen cycling in saline lakes, urging its integration into biogeochemical models under climate change scenarios.