In-canopy throughfall measurements of ion fluxes in Norway spruce

Abstract

Canopy throughfall was collected at four distances from the tree trunk and at six depths in the canopy of a Norway spruce forest at Klosterhede, Denmark. Forty-five series of throughfall were collected during the years 1992 and 1993. The samples were analyzed for pH, Na +, K +, Ca 2+, Mg 2+, NH 4 +, Cl −, NO 3 −, and SO 4 2−. The smallest quantity of throughfall was sampled closest to the tree trunk, and the largest quantity of 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 decreased as a function of the distance from the nearest tree trunk. The lowest fluxes were observed in the upper canopy, and they increased down through the canopy. A negative net throughfall of NH 4 + indicated an uptake of NH 4 + in the canopy in the growing season. The measurements also indicated an uptake of NO 3 − at some positions in the canopy, but only during the growing season. The uptake of NH 4 + was negatively correlated to the fluxes of NH 4 + in precipitation. Leaching of K +, Ca 2+, and Mg 2+ was accumulated to be highest in the lower canopy. Potassium was leached in larger amounts than Ca 2+, which again was leached in a greater amount than Mg 2+. Potassium leached from the trees in large amounts even during the dormant season.