34S natural abundance variations in prairie and boreal forest soils

SUMMARY The systematic nature of the 34S natural abundance variations (δ34S) in a prairie and boreal forest ecosystem enabled construction of hypotheses regarding the origin and cycling of S in the two soil-plant systems. By considering the 34S abundance variations in relation to soil S transformations, a better understanding of S isotope fractionation in soils was also achieved. The δ34S values suggest that atmospheric S becomes increasingly more important as a S input as pedogenesis proceeds in these soils. The origin and movement of sulphate salt in a saline seep was evaluated using δ34S values, demonstrating the usefulness of the δ34S technique in soil salinity studies. The 34S-enrichments and depletions found in soil organic S fractions were consistent with postulated differences in lability, mobility, and turnover rate. Wheat plants growing on the saline, sulphate-saturated prairie soil were found to be enriched in 34S relative to surrounding S sources, providing indirect evidence for release of 34S-depleted H2S by the plants as a S-stress relief mechanism.