Microbial community composition changes linked to volatile sulfur compound emissions

Volatile sulfur compounds (VSCs) contribute to acid rain, cloud formation, and albedo, and thusinfluence the climate. Their global emissions are still quite uncertain, especially contributionsfrom freshwater wetlands. We investigated the processes leading to hydrogen sulfide (H 2 S),methanethiol (MeSH), and dimethyl sulfide (Me 2 S) emissions in a slightly acidic peatland andfound multiple indications that organic matter degradation rather than sulfate reduction is themain driver for Me 2 S emissions in this system. Evidence includes: the lack of labelled Me 2 34 Sproduction after addition of Na 2 34 SO 4 despite high emissions of Me 34 SH and H 2 34 S, and increasedemission rates when soils were amended with organic substrates containing thiol groups (H 2 Semissions), methylthiols (MeSH), and dimethyl sulfonio groups (Me 2 S). VSC precursors wereidentified from an Untargeted Metabolomics data set from the same soil. The abundance ofsulfur cycling microbes like Acidobacteria SD 1 and Desulfosporosinus correlated with VSCemissions. We conclude that organic matter degradation is more important than sulfate reductionas a source of Me 2 S in our peatland system, and potentially also in other organic and wetlandsoils.