|Brumme, R; Leimcke, U; Matzner, E: Interception and uptake of NH|
Uptake of NH 4 and NO 3 by above ground parts of beech trees was studied by spraying young trees with varying concentrations of ZSN labeled solutions, different N-forms, and spray regimes over four months. Following treatment, the trees were harvested and analyzed for 15N and major element content. Throughfall was collected and analyzed in addition in order to study the interaction between nitrogen uptake and cation leaching. Significant amounts of N were taken up by the above ground plant parts in all treatments as indicated by 15N analysis of the trees as well as by throughfall measurements. NH 4 uptake exceeded the uptake of NO 3 if applied in the same concentration. Uptake of N increased linearly with increasing concentration in the spray solution and with spray intensity. The uptaken N was translocated within the plant. The contribution of N from uptake by above ground parts to the total N content of tissues differed and reached a maximum level of 6% in leaves. No effect of above ground N uptake on the total N content of tissues was found. Calculating atmospheric N inputs to forest ecosystems by throughfall measurements may underestimate the actual N input.