Sulfate-Dependent Mechanisms of Dimethyl Sulfide Release in Freshwater Ecosystems: Evidence from Field and Experimental Studies

Algae mediate the biogeochemical sulfur cycle by releasing dimethyl sulfide (DMS), a process with significant implications for the global climate. Previous studies have indicated a correlation between DMS release and sulfate (SO₄^2-) concentrations in lakes─critical hotspots for global DMS emissions─yet the mechanisms remain poorly understood. This study examined 35 lakes near the Yangtze River, revealing a significant increase (P < 0.05) in a DMS yield (DMS/Chla) with rising SO₄^2- (8.10 to 114.00 mg/L). Validation experiments using the dominant algal species, Microcystis aeruginosa, showed that increasing SO₄^2- (0 to 160 mg/L) significantly boosted DMS concentration by day 18, from 10.55 ± 4.37 to 1673.94 ± 702.96 ng/L, with a maximum yield at 80-160 mg/L SO₄^2- (P < 0.05). Transcriptome sequencing of M. aeruginosa revealed that elevated SO₄^2- significantly upregulated genes related to sulfur metabolism, including those encoding ABC transporters, gluthathione synthase, carbamoyl transferase, and aminomethyltransferase glycine dehydrogenase, suggesting that enhanced sulfur uptake and metabolic capacity may promote algal DMS synthesis and release. This study elucidates the effects of SO₄^2- on freshwater algal DMS release and explores the underlying mechanisms, offering insights into aquatic sulfur cycling and a foundation for addressing climate challenges.