Zusammenfassung
Temporal changes in inorganic and organic sulfur compounds (sulfate, glutathione, cysteine, methionine) were analyzed in xylem sap of 40-year-old Norway spruce (Picea abies (L.) Karst.) trees growing on acidic soils at a healthy and a declining stand in the Fichtelgebirge (North Bavaria, Germany). Studies were carried out (1) to quantify glutathione (GSH) transport in the xylem of spruce, (2) to study the significance of reduced sulfur versus sulfate (SO42–) transport in the xylem, and (3) to compare total sulfur (S) transport in the xylem with the amount of foliar uptake of SO2 in an air-polluted environment. Glutathione was the main reduced S compound in the xylem ranging in concentration from 0.5 to 5 μmol l−1. Concentrations of inorganic SO42– in the xylem sap were up to 50 times higher than those of GSH ranging from 60 to 230 μmol l−1. During the growing season, concentrations of all S compounds in the xylem were highest in May (up to 246 μmol l−1) and decreased during summer and fall (up to 21 μmol l−1). On average, SO42– concentrations in xylem sap were 30% higher at the declining site compared with the healthy site. Diurnal changes in organic S compounds were significant for GSH and cysteine with high concentrations during the night and low concentrations during the day. Diurnal changes in inorganic concentrations were not significant. Xylem sap concentrations of SO42– and cysteine were twice as high and GSH concentrations were tenfold higher in surface roots than in branches. At both sites, transport of organic S was low (up to 3% of total S) compared to transport of SO42–. Annual transport of total S in the xylem (SO42– was the main component) ranged from 60 to 197 mmol tree−1 year−1 at the healthy site and from 123 to 239 mmol tree−1 year−1 at the declining site. Although gaseous uptake of SO2 was estimated to be similar at both sites (38 mmol tree−1 year−1; Horn et al. 1989), the ratio between annual gaseous uptake of SO2 and transport of S in the xylem was 1:4 and 1:5 at the healthy and declining sites, respectively.
