Beschreibung:
Mangrove ecosystems serve as an important carbon sink but also could be a hotspot that produces neurotoxic methylmercury (MeHg). Although many studies have focused on mercury (Hg) contamination in this carbon-rich ecosystem, our understanding of the effects and mechanisms of the organic matter (OM) regulation of MeHg production in mangrove sediments is still limited. Here, we examined the effects of Hg contamination and OM enrichment on MeHg production in anoxic mangrove sediments and identified the major microbial guilds attending this process. The mangrove sediments possessed a high potential for producing MeHg, but this was counterbalanced by its rapid degradation. Sulfate-reducing bacteria (SRB) such as Desulfobacterales , Desulfovibrionales , and Syntrophobacterales were the major methylators. OM diagenesis significantly changed the biogeochemical conditions, accelerating MeHg removal in the sediments. The enhanced MeHg demethylation was attributable to the abundant sulfide produced during OM decomposition, which potentially inhibited the Hg methylation by immobilization of inorganic Hg, abiotically degraded MeHg, and favored the non- mer -mediated degradation of MeHg by SRB (e.g., Desulfosarcina and Desulfatiferula ). Our study provides both geochemical and microbial clues that can partly explain the low MeHg levels widely observed in mangrove sediments