Salinization of coastal saline-alkali soil might enhance H2S release by affecting H2S-related bacterial communities

Bacterial metabolism can result in the production and release of hydrogen sulfide (H2S), a reductive gas, in soils. Hydrogen sulfide-releasing bacteria (HSRB) assimilate organic sulfur or dissimilate sulfate to generate and release H2S, whereas H2S-oxidizing bacteria (HSOB) oxidize H2S generated by themselves or other bacteria to soluble sulfate resulting in sulfur retention in soil. However, the effects environmental factors such as electrical conductivity on both these bacterial groups and H2S release remain unclear; some key processes such as H2S oxidation also remain underexplored. In this study, we found that high electrical conductivity in coastal saline-alkali soil affects these bacterial communities, especially HSRB, potentially enhancing H2S release. The “sink” of H2S gas, represented by sulfidic sulfur (concentration, 0.2–3.4 nmol/g) in coastal saline-alkali and inland soils, was determined using the methylene blue method, and found to be positively correlated with soil electrical conductivity, suggesting that more H2S gas potentially volatilized from salinized soil. We then revealed that the proportion of HSRB clones was correlated positively and significantly with the electrical conductivity and sulfidic sulfur of soil, but not with the pH or sulfur source. Further, 16S rRNA gene sequence comparison indicated significantly reduced richness and diversity of bacterial communities and considerably altered the composition of dominant bacterial populations in coastal saline-alkali soil. The phyla Proteobacteria, Bacteroidetes, and Gemmatimonadetes accounted for 38 %, 30.1 %, and 11.1 % and for 28 %, 12.9 %, and 2.5 % of the bacterial populations in coastal saline-alkali and inland soil, respectively. PICRUSt analysis showed that the richness of genes encoding the key H2S oxidation enzymes, sulfide:quinone reductase and sulfate hydrolase, was decreased significantly and negatively correlated with the detected sulfidic sulfur. These enzymes are usually expressed by HSOB in coastal saline-alkali soil, implying a low sulfide oxidation capacity. These results indicate that the number of HSRB is increased whereas the ability of H2S oxidation is decreased in coastal saline-alkali soil, which might lead to enhanced H2S release. Overall, this study provides new insights for understanding the sulfur biological cycle in saline-alkali soils.