Spartina alterniflora raised sediment sulfide in a tidal environment and buffered it with iron in the Jiuduansha Wetland

The extensive invasion of Spartina alterniflora in coastal wetlands of China has posed a ruinous risk to biodiversity and ecosystem constancy. Sulfur is an essential nutrient, while sulfide is biologically toxic and could couple with iron. The influence of S. alterniflora invasion on sulfur and iron cycling in sediment remains poorly understood. Hence, the purpose of this study is to investigate how the invasion of S. alterniflora affects the sulfur and iron cycles in sediments in coastal wetlands. Field investigations were conducted in the Jiuduansha Wetland to examine the different sulfur and iron components, microbial communities, and functional genes related to the sulfur cycle in soils colonized by S. alterniflora and in native coenosis. The invasion of S. alterniflora caused the accumulation of reduced inorganic sulfur (RIS) in the sediments, and the RIS components were stratified at different sediment depths. The activity of S. alterniflora roots and the presence of low-elevation tides promoted sulfate reduction and the accumulation of acid volatile sulfide (AVS), primarily through abiotic chemical processes. These processes facilitated the invasion and expansion of S. alterniflora. Meanwhile, S. alterniflora could promote sulfate reduction by altering sediment physicochemical properties, such as pH. However, the correlation between RIS components and salinity or Eh in the low-intertidal zones was not significant due to the influence of tidal action. Nevertheless, S. alterniflora could buffer sulfide by enriching Fe, rapidly reducing Fe(III) and forming pyrite, thus mitigating sulfide stress. The invasion of S. alterniflora in tidal environments increased sediment sulfide levels, while S. alterniflora is able to mitigate the effects of sulfide stress on itself by efficiently utilizing iron.