Dynamics of DOC and DON in forest soils

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Michalzik, Beate ; Küsel, Kirsten ; Solinger, Stephan ; Matzner, Egbert:
Dynamics of DOC and DON in forest soils.
In: Mitteilungen der Deutschen Bodenkundlichen Gesellschaft. Bd. 87 (1998) . - S. 225-236.
ISSN 0343-107x

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Abstract

DOC (dissolved organic carbon) is defined operationally as < 0.45 mikrom filtrates. It consists of a continuum of organic substances ranging from defined small organic molecules to highly polymeric and amorphous humic substances. The importance of DOC for nutrient translocation, proton buffering and soil genesis is beyond question. Several studies have recently focused on the quantification of DOC fluxes and budgets under field conditions. This review will concentrate on two major questions:1) What is the relevance of DOC as C input into the mineral soil and as a source for Refractory Soil Organic Matter (RSOM)?In temperate forest ecosystems, the annual fluxes of DOC from the forest floor into the mineral soil vary from 120-500 kg C ha-1yr-1. Since decomposition rates of DOC were found to be very low, DOC seems to be largely composed of refractory substances. Thus, DOC inputs from the forest floor might be an important source of RSOM in forest mineral soils.2) What are the regulating factors for the DOC/DON dynamics in various ecosystems?The DOC and DON (dissolved organic nitrogen) concentrations and fluxes in throughfall and forest floor solutions were found highly variable in time and space depending on field and soil conditions. Only a few studies combined field observations, laboratory experiments and structural characterization to identify processes and factors influencing DOC/DON release and consumption in forest ecosystems. A comparison of field and laboratory data often reveals contradicting results with respect to controlling factors. Whereas findings from laboratory studies indicate a higher DOC release with increasing pH, decreasing conductivity or increasing temperature, this was not easily confirmed under field conditions.The importance of regulating factors may change depending on the time and space scale considered. Furthermore the quality of DOC (e.g. contribution of low molecular weight organic acids to DOC) changes with temporal resolution of the measurements.Future research should address the regulation of the long term release of DOM from forest floors for a better understanding of DOM contribution to RSOM formation. This should include different environmental conditions and litter qualities as well as physico-chemical controls vs. biological processes.