Seasonal variation in throughfall and stemflow chemistry beneath a European beech (Fagus sylvatica) tree in relation to canopy phenology

The effect of canopy phenology on major ion fluxes beneath a mature European beech (Fagus sylvatica L.) tree is examined. Annual and seasonal ion fluxes to the forest floor were significantly higher than the incoming wet-only deposition for all ions measured other than H⁺. The annual throughfall to wet deposition ratio generally ranged from 2.1 to 4.8. Stemflow contributed 9%–19% of the ion input to the forest floor, except for H⁺. Throughfall enrichment of K⁺, Ca²⁺, Mg²⁺, and NO₃^– was significantly higher in the leafed than in the leafless season, in contrast to Na⁺, NH₄⁺, and H⁺. The temporal pattern of ion enrichment indicated canopy release of K⁺, Ca²⁺, and Mg²⁺ throughout the leafed season, of Na⁺, Cl^–, and NH₄⁺ from emerging leaves, and of Cl^– and SO₄^2– from senescing leaves. The contribution of canopy leaching to annual net throughfall and stemflow was estimated at 96% (K⁺), 54% (Ca²⁺), 40% (Mg²⁺), 12% (Cl^–), and 7% (Na⁺, SO₄^2–). Dry deposition accounted for 58%–75% of the total deposition onto the canopy. The throughfall enrichment during the leafless season indicated high particulate and gaseous dry deposition onto the woody canopy as well as K⁺ release from European beech branches.