Biodegradability of dissolved organic matter extracted from a chronosequence of forest-floor materials

Dissolved organic matter (DOM) is an important part of the microbially utilizable organic matter in soils. This paper describes an incubation experiment by which the lability and mobility of DOM extracted from forest-floor materials are related to their age and degree of degradation. DOM extracted from a chronosequence of decomposing leaves (green leaves, fresh fallen leaves, litter [1 y weathering], fibric matter [2-3 y], hemic matter [> 3 y], or peat [100+ y]) was applied to intact soil cores, and the CO2 produced over 5 d was measured to determine biodegradability. Biodegradability of DOM varied somewhat along the chronosequence, with the green leaves yielding more CO2 on an equal C basis than the older substrates and equivalent to glucose which was used as a reference substrate. Thus, the DOM extracts of the older substrates contain some refractory components. The humic-acid content (or that of its precursors) of the extracts from older substrates relates to the lowered lability. The hydrophobic and hydrophilic content of DOM extracted from substrates was not related to CO2 production in the incubation studies conducted.