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Faculty for Biology, Chemistry and Earth Sciences

Department Soil Ecology - Prof. Dr. Eva Lehndorff

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Solinger, St; Kalbitz, K; Matzner, E: Fluxes and concentrations of dissolved organic matter in a Central European beech (Fagus sylvatica L.) ecosystem, Biogeochemistry, 55, 327-349 (2001)
Despite growing attention concerning the role of dissolved organic matter (DOM) in element cycling of forest ecosystems, the controls of concentrations and fluxes of both dissolved organic carbon (DOC) and nitrogen (DON) under field conditions in forest soils remain only poorly understood. The goal of this project is to measure the concentrations and fluxes of DON, NH+4 , NO−3 and DOC in bulk precipitation, throughfall, forest floor leachates and soil solutions of a deciduous stand in the Steigerwald region (northern Bavaria, Germany). The DOC and DON concentrations and fluxes were highest in leachates originating from the Oa layer of the forest floor (73 mg C L−1, 2.3mg N L−1 and about 200–350 kg C, 8–10 kg N ha−1 yr−1). They were observed to be highly variable over time and decreased in the mineral topsoil (17 mg C L−1, 0.6mgN L−1 and about 50–90 kg C, 2.0 to 2.4 kg N ha−1 yr−1). The annual variability of DOC and DON concentrations and subsequential DOC/DON ratios was substantial in all solutions. The DOC and DON concentrations in throughfall were positively correlated with temperature. The DOC and DON concentrations did not show seasonality in the forest floor and mineral soil. Concentrations were not related to litterfall dynamics but did correspond in part to the input of DOC and DON from throughfall. The throughfall contribution to the overall element fluxes was higher for DON than for DOC. Concentrations and fluxes of DON were significantly correlated to DOC in throughfall and the Oi layer. However, the correlation was weak in Oa leachates. In addition, seasonal and annual variation of DOC/DON ratios indicated different mechanisms and release rates from the forest floor for both components. The concentrations of DOC and DON in forest floor leachates were in most cases dependent neither on the pH value or ionic strength of the solution, nor on the water flux or temperature changes. As a consequence, the DOC and DON fluxes from the forest floor into the mineral soil were largely dependent on the water flux if annual and biweekly time scales are considered.
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