Abstract

Bulk precipitation, throughfall and stemflow of base cations Na +, K+, Mg2+ and Ca2+ were measured in two deciduous beech forests, located in regions with different air pollution characteristics and strongly differing in soil acidity and soil base saturation. The contribution of dry deposition and canopy leaching to net throughfall flux was estimated using Na+ as a tracer ion. The input of base cations via bulk precipitation was not significantly different between Nothofagus obliqua (Mirb.) Bl. in southern Chile and Fagus sylvatica L. in Flanders. However, net throughfall input of Ca2+ and Mg2+ to the forest floor was significantly higher in Chile than in Flanders. Potassium fluxes were similar in both studied stands. Dry deposition of Ca2+ was higher in Chile, in absolute value as well as in relative contribution to net throughfall flux. A strong difference between the two Fagaceae-dominated forests was found for magnesium. In Chile, canopy leaching of Mg2+ (8.9 kg ha-1 y-1) was the major input source to the forest floor, while Mg 2+ canopy leaching was close to zero in Flanders. As the availability of base cations in the soil solution determines the possibility of trees to exchange cations, we hypothesize that the lower Mg2+ canopy leaching in Flanders is mainly due to magnesium deficiency in the Flemish forest soil.