Regulation of coupled carbon‑sulfur interactions by Spartina alterniflora via physicochemical properties and microorganism-mediated pathways in coastal wetlands

The invasive species Spartina alterniflora has profoundly altered biogeochemical cycling in coastal wetlands across China since its introduction decades ago. This study examined its impacts on spatiotemporal patterns of carbon and sulfur storage in intertidal sediments. Through systematic field sampling and laboratory analyses, we quantified seasonal variations in vertical sediment profiles across three distinct zones in Jiaozhou Bay wetlands: S. alterniflora-invaded area (SAA), native Suaeda glauca area (SGA), and unvegetated mudflat area (MA). Key parameters included dissolved organic carbon (DOC), soil organic matter (SOM), total carbon (TC), four inorganic sulfur forms (water soluble sulfur, adsorbed sulfur, hydrochloric acid soluble sulfur, hydrochloric acid volatile sulfur), and total sulfur (TS). Our findings revealed that SAA exhibited significantly higher DOC (16–107 %) and TC (18–21 %) concentrations compared to SGA and MA. TS accumulation in SAA surpassed the other two areas by 1.4- to 1.6-fold, with particularly large fractions of water-soluble sulfur (17–32 %) and hydrochloric acid volatile sulfur (52–133 %). Notably, SOM/TS ratios in SAA were significantly lower in winter and summer (28–37 %) than in native ecosystems. These results demonstrate that S. alterniflora invasion fundamentally restructures coastal sediment geochemistry through coupled carbon–sulfur interactions, with implications for wetland biogeochemical functioning under biological invasions.