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

摘要

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 SO42- 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+, SO42-). 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.