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Faculty for Biology, Chemistry and Earth Sciences

Department Soil Ecology - Prof. Dr. Eva Lehndorff

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Michalzik, B; Matzner, E: Dynamics of dissolved organic nitrogen and carbon in a Central European Norway spruce ecosystem, European Journal of Soil Science, 50, 579-590 (1999)
Dissolved organic nitrogen and carbon (DOC) are significant in the C and N cycle in terrestrial ecosystems. Little is known about their dynamics in the field and the factors regulating their concentrations and fluxes. We followed the fluxes and concentrations of the two in a Norway spruce (Picea abies [L.] Karst.) forest ecosystem in Germany from 1995 to 1997 by sampling at fortnightly intervals. Bulk precipitation, through-fall, forest floor percolates from different horizons and soil solutions from different depths were analysed for major ions, dissolved organic N and DOC. The largest fluxes and concentrations were observed in percolates of the Oi layer, which contain 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 with time and decreased with depth. The largest fluxes in forest floor percolates occurred when the snow melted. The concentrations and fluxes of DON were significantly correlated to DOC, however the correlation was weak, indicating different mechanisms of release and consumption. The dynamics of neither dissolved organic N nor DOC in forest floor percolates were explained by pH and ionic strength of the soil solution or by the water flux despite large variations of these. Furthermore, the release of these fractions from the forest floor was not related to the quality and amount of through-fall. Concentrations of dissolved organic N in forest floor percolates increased with soil temperature, while temperature effects on DOC were less pronounced, but their fluxes from the forest floor were not correlated with temperature. In the growing season concentrations of both dissolved organic N and C in forest floor percolates decreased with increasing intensity of through-fall. 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 DOC in the N and C cycle of forest ecosystems.
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