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Faculty for Biology, Chemistry and Earth Sciences

Department Soil Ecology - Prof. Dr. Eva Lehndorff

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Solinger, St; Matzner, E: Dynamics of DOC and DON mobilization in a deciduous forest ecosystem, Mitteilungen der Deutschen Bodenkundlichen Gesellschaft, 87, 295-296 (1998)
Dissolved organic matter (DOM) is a topic of growing interest with respect to global element cycles, pedogenesis and ecosystem functions. Despite of that, the fluxes and dynamics of DOM have been studied only in a few cases. Particularly for Central Europe information is scarce. In this study, element fluxes were measured in a deciduous forest stand in the Steigerwald in north-eastern bavaria. Objectives were to assess the contribution of dissolved organic carbon (DOC) and nitrogen (DON) to the element fluxes into the mineral soil, to investigate the seasonal variation of these element fluxes and to elucidate key parameters for the mobilization of DOC and DON. For this purpose bulk precipitation, throughfall solution and forest floor leachates from the Oi and Oa layers were collected with plastic funnels and low-tension suction plate lysimeters respectively and sampled in biweekly intervals. All samples were measured for pH and electrical conductivity, filtered by 0.45 µm cellulose acetate filters and subsequently analysed for DOC, total N and mineral N. DON was calculated by difference N tot-N min. On the same site element contents of litterfall were measured throughout the year. Results obtained by this investigation show, that DOC and DON represent about 12% and 9% of total C and N fluxes into the mineral soil respectively. Concentrations increased for all measured components from bulk precipitation to Oa leachate. The major source of DOC (306 kg/ha*y), DON (13 kg/ha*y) and nitrate (66 kg/ha*y) was the Oa layer. Seasonal variations in DOC and DON fluxes showed no regular pattern but were closely associated with the amount of precipitation. Periods of high element fluxes appeared during all seasons. Up to 10 % of yearly fluxes could be measured in individual fortnightly samples. The dynamics of DOC and DON fluxes indicated no difference in mobilization mechanisms of the both components either in throughfall or forest floor leachate. Pearson correlation coefficients showed no significant correlation of DOC or DON concentrations to either water flux, solution pH or electrical conductivity for Oi and Oa leachates. This questions the significance of these solution parameters for the mobilization of DOM from the forest floor. Future research should address further environmental factors such as temperature and water budget as well as different time scales to identify key parameters of DOM mobilization and the interaction of biotic and abiotic controls. Dynamics of DOC and DON mobilization in a Deciduous Forest Ecosystem
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