Short-term canopy interactions of beech trees: mineral ion leaching and absorption during rainfall.

Mineral nutrient composition of the stemflow of 70-120-year-old beech trees Fagus sylvatica L. in 26 stands in northwestern Switzerland was compared with that of incident precipitation. Four mm of precipitation was sufficient to wash-off the bulk of the dry deposition intercepted by the canopy. Thereafter, differences in composition between precipitation and stemflow provided a measure of net ion absorption by or leaching from the canopy. Depending on the acidity of the rain and on the buffering of protons by the canopy, different interactions were observed. Highest rates of leaching were detected for potassium whereas ammonium was absorbed in some stands and leached in others. Absorption of chloride was associated with the occurrence of H(+) buffering. The latter took place to a greater extent in more acidic precipitations. Interrelations of short-term canopy ion interactions are discussed and some implications examined.