THE SYNERGISM BETWEEN SO2 OXIDATION AND MANGANESE LEACHING ON SPRUCE NEEDLES - A CHAMBER EXPERIMENT

Four year old spruce (Picea abies (L.) Karst.) seedlings were planted in sand pots and supplied with nutrient solution. Three groups were fo rmed, differing only in manganese nutrition (0.5 ppm, 2.5 ppm, 12.5 pp m, respectively). After three months, five individuals of each group w ere transferred to a dew chamber. For the next seven weeks the trees w ere sprayed in the evenings, the relative humidity overnight was kept high and the droplets were collected directly from the needles in the mornings. The trees were sprayed with HNO3 (pH 3.4) during the first t hree weeks to reduce the natural buffering capacity of the needles. Af ter this time, the trees were sprayed with KCI (1 mM) solution, and Na HSO3 was added to the chamber resulting in SO2 concentrations usually between 50 and 150 mu g m(-3) Needles and water samples were analysed. Foliar Ca seemed to be only a short-time buffer even under optimal Ca supply. A highly significant influence of manganese supply on mangane se in needles and droplets was observed, as well as on sulphate, H+ an d calcium concentrations in the droplets. The SO2 flux to trees treate d with 12.5 ppm Mn was about twice as high as to trees treated with 0. 5 ppm Mn. The conclusion is that this is due to a synergism between ma nganese leaching and catalysis of the SO2 oxidation by the leached Mn2 + ions. The results suggest a positive feedback between (moderate) aci dification of soils and SO2 and NH3 inputs to terrestrial ecosystems. (C) 1997 Elsevier Science Ltd.