We investigated speciation, oxidative state changes, and longand short-term molecular-level dynamics of organic S after 365 d of aerobic incubation with and without theaddition of sugarcane residue using XANES spectroscopy. Soil samples were collected from theupper 15 cm of undisturbed grasslands since 1880, from undisturbed grasslands since 1931, and from cultivated fields since 1880 in thewestern United States. We found three distinct groups of organosulfur compounds in these grassland-derived soils: (i) strongly reduced (S0 to S1+) organic S that encompasses thiols, monosulfides, disulfides, polysulfides, and thiophenes; (ii) organic S in intermediate oxidation (S2+ to S5+) states, which include sulfoxides and sulfonates; and (iii) strongly oxidized (S6+) organic S, which comprises ester-SO4-S. Th e first two groups represent S directly linked to C and accounted for 80% of thetotal organic S detected by XANES from theundisturbed soils. Aerobic incubation without theaddition of sugarcane residue led to a 21% decline in organanosulfur compounds directly linked to C and to up to an 82% increase inorganic S directly bonded to O. Among theC-bonded S compounds, low-valence thiols, sulfides, thiophenic S, and intermediate-valence sulfoxide S seem to be highly susceptible to microbial attack and may represent themost reactive components of organic S pool in these grassland soils. Sulfonate S exhibited a much lower shortterm reactivity. Th e incorporation of sugarcane residue resulted in an increase in organosulfur compounds directly bonded to C at theearly stage of incubation. However, similar to soils incubated without residue addition, theproportion of organic S directly linked to C continued to decline with increasing duration of aerobic incubation, whereas theproportion of organic S directly bonded to O showed a steady rise.
All Science Journal Classification (ASJC) codes
- Environmental Engineering
- Water Science and Technology
- Waste Management and Disposal
- Management, Monitoring, Policy and Law