Dimethyl Sulfide Emissions From a Peatland Result More From Organic Matter Degradation Than Sulfate Reduction

Volatile sulfur compounds (VSCs) contribute to acid rain, cloud formation, and albedo, and thus influence the climate. Their global emissions are quite uncertain, especially contributions from 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 and found multiple indications that organic matter degradation rather than sulfate reduction is the main driver for Me 2 S emissions in this system. Evidence includes: the lack of labeled Me 2 34 S production after addition of Na 2 34 SO 4 despite high emissions of Me 34 SH and H 2 34 S, and increased emission rates when soils were amended with organic substrates containing thiol groups (H 2 S emissions), methylthiols (MeSH), and dimethyl sulfonio groups (Me 2 S). VSC precursors were identified from an Untargeted Metabolomic s data set from the same soil. The abundance of sulfur cycling microbes like Acidobacteria SD 1 and Desulfosporosinus correlated with VSC emissions. We conclude that organic matter degradation is more important than sulfate reduction as a source of Me 2 S in our peatland system, and potentially also in other organic and wetland soils.