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Faculty for Biology, Chemistry and Earth Sciences

Department Soil Ecology - Prof. Dr. Eva Lehndorff

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Scheel, T; Pritsch, K; Schloter, M; Kalbitz, K: Precipitation of enzymes and organic matter by aluminium - impacts on carbon mineralization, Journal of Plant Nutr. Soil Sci., 171, 900-907 (2008), doi:DOI: 10.1002/jpln.200700146
The precipitation of dissolved organic matter (DOM) by aluminum (Al) results in a stable soil organic matter (OM) fraction. Extracellular enzymes can also be removed from soil solution by sorption or precipitation, but whether this affects their activity and their importance for carbon (C) mineralization is largely unknown. We studied the activity of eight extracellular enzymes, precipitated by Al together with DOM, in relation to C mineralization of the precipitated OM. Dissolved OM was obtained from the Oi and Oa horizon of two forest soils and precipitated at different Al : C ratios and pH values to achieve a large variation in composition and C mineralization of precipitated OM. All eight enzymes were present in a functional state in precipitated OM. On average 53% of DOM was precipitated, containing on average 17%-41% of the enzyme activity (EA) involved in C degradation (chitinase, cellobiohydrolase, -glucosidase, glucuronidase, lacasse, and xylosidase) previously present in soil solution. In contrast, on average only 4%-7% of leucine-aminopeptidase and acid-phosphatase activity was found in precipitated OM. The EA found in precipitates significantly increased the percentage of C mineralized of precipitated OM, with a stronger influence of C-degrading enzymes than enzymes involved in N and P cycling. However, after 8 weeks of incubation the correlations between EA and C mineralization disappeared, despite substantial EA being still present and only 0.5%-7.7% of C mineralized. Thus, degradation of precipitated OM seems to be governed by EA during the first degradation phase, but the long-term stability of precipitated OM is probably related to its chemical properties.
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