Dynamics of dissolved organic nitrogen and carbon in a Central European Norway spruce ecosystem

Dissolved organic nitrogen and carbon (DOC) are significant in the C and N cycle in terrestrial ecosystems. Little is known about their dynamics in th e field and the factors regulating their concentrations and fluxes. We foll owed the fluxes and concentrations of the two in a Norway spruce (Picea abi es (L.) Karst.) forest ecosystem in Germany from 1995 to 1997 by sampling a t fortnightly intervals. Bulk precipitation, throughfall, forest floor perc olates from different horizons and soil solutions from different depths wer e analysed for major ions, dissolved organic N and DOC. The largest fluxes and concentrations were observed in percolates of the Oi layer, which conta in amino N and amino sugar N as the major components. The average ratio of dissolved organic C to N in forest floor percolates corresponded to the C/N ratio of the solid phase. Concentrations and fluxes were highly dynamic wi th time and decreased with depth. The largest fluxes in forest floor percol ates occurred when the snow melted. The concentrations and fluxes of dissol ved organic N were significantly correlated with DOC, but the correlation w as weak, indicating different mechanisms of release and consumption. The dy namics of dissolved organic N and DOC in forest floor percolates were not e xplained by pH and ionic strength of the soil solution nor by the water flu x, despite large variations in these. Furthermore, the release of these fra ctions from the forest floor was not related to the quality and amount of t hroughfall. Concentrations of dissolved organic N in forest floor percolate s increased with soil temperature, while temperature effects on DOC were le ss pronounced, but their fluxes from the forest floor were not correlated w ith temperature. In the growing season concentrations of both dissolved org anic N and C in forest floor percolates decreased with increasing intensity of throughfall. Thus, the average throughfall intensity was more important than the amount of percolate in regulating their concentrations in forest floor percolates. Our data emphasize the role of dissolved organic N and DO C in the N and C cycle of forest ecosystems.