IN-CANOPY THROUGHFALL MEASUREMENTS OF ION FLUXES IN NORWAY SPRUCE

Canopy throughfall was collected at four distances from the tree trunk and al six depths in the canopy of a Norway spruce forest at Klosterh ede, Denmark. Forty-five series of throughfall were collected during t he years 1992 and 1993. The samples were analyzed for pH, Na+, K+, Ca2 +, M(2+), NH4+, Cl-, NO3-, and SO42-. The smallest quantity of through fall was sampled closest to the tree trunk, and the largest quantity o f throughfall was sampled in the periphery of the canopy at all levels in the canopy. The quantity of throughfall was highest at the top of the tree and decreased down through the canopy. The highest fluxes of all ions were observed close to the tree trunk, and the fluxes decreas ed as a function of the distance from the nearest tree trunk. The lowe st fluxes were observed in the upper canopy, and they increased down t hrough the canopy. A negative net throughfall of NH4+ indicated an upt ake of NH4+ in the canopy in the growing season. The measurements also indicated an uptake of NO3- at some positions in the canopy, but only during the growing season. The uptake of NH4+ was negatively correlat ed to the fluxes of NH4+ in precipitation. Leaching of K+, Ca2+, and M g2+ was accumulated to be highest in the lower canopy. Potassium was l eached in larger amounts than Ca2+, which again was leached in a great er amount than Mg2+. Potassium leached from the trees in large amounts even during the dormant season. Copyright(C) 1996 Elsevier Science Lt d