Fractionation of sulfur (S) in beech () forest soils in relation to distance from the stem base as useful tool for modeling S biogeochemistry.

The investigation of the fractionation of S compounds in forest soils is a powerful tool for interpreting S dynamics and S biogeochemistry in forest ecosystems. Beech stands on high pH (nutrient-rich) sites on Flysch and on low pH (nutrient-poor) sites on Molasse were selected for testing the influence of stemflow, which represents a high input of water and dissolved elements to the soil, on spatial patterns of sulfur (S) fractions. Soil cores were taken at six distances from a beech stem per site at 55 cm uphill and at 27, 55, 100, 150 and 300 cm downhill from the stem. The cores were divided into the mineral soil horizons 0-3, 3-10, 10-20, 20-30 and 30-50 cm. Soil samples were characterized for pH, C, pedogenic Al and Fe oxides and S fractions. Sequential extraction by NHCl, NHHPO and HCl yielded readily available sulfate-S (), adsorbed sulfate-S () and HCl-soluble sulfate-S (). Organic sulfur () was estimated as the difference between total sulfur () and inorganic sulfur ( + + ). Organic sulfur was further divided into ester sulfate-S (, HI-reduction) and carbon bonded sulfur (). On Flysch, represented 3-6%, 2-12%, 0-8% and 81-95% of . On Molasse, amounted 1-6%, 1-60%, 0-8% and 37-95% of . Spatial S distribution patterns with respect to the distance from the tree stem base could be clearly observed at all investigated sites. The presented data is a contribution to current reports on negative input-output S budgets of forest watersheds, suggesting that mineralization of on nutrient rich soils and desorption of historic on nutrient-poor soils are the dominant S sources, which have to be considered in future modeling of sulfur.