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Characteristics of dissolved organic matter and its stabilization in forest soil.
Yano, Yuriko1, Lajtha, Kate2, Sollins, Phil1, Caldwell, Bruce1, Spears, Julie2, 1 2
ABSTRACT- Stabilization of dissolved organic matter (DOM) via abiotic adsorption is an important process for soil organic matter (SOM) formation. We investigated the effects of detritus type on DOM chemistry and DOM adsorption to mineral soil in an old-growth Douglas-fir forest in the Pacific Northwest, OR. Chemical fractionation of DOM extracted from different types of Douglas-fir litter (new or decomposed leaf and wood, and new fine root) showed considerable differences in DOM chemistry across tissue types within new type litter. Leaf litter extracts generally had a greater hydrophilic acid content than wood litter extracts. The degree of decomposition had a stronger effect on DOM chemistry than differences in tissue type. As litter decomposes the proportions of hydrophobic acid and base fractions increased, and the hydrophilic neutral fraction decreased. These differences across tissue types were not found for the chemical compositions of O horizon leachate collected in a long-term litter input plots (2x leaf, 2x wood and natural inputs). This may indicate that the decomposition of litter in forest floor contributes to the production of relatively homogenous DOM that leaches into the mineral soil. Field observation suggests preferential removal of hydrophobic acids in the B-horizon, regardless of the season. The lab incubation of the various litter extracts and B-horizon soil also showed preferential removal of the hydrophobic acid fraction. The implication of the results on SOM formation will be discussed.
KEY WORDS: dissolved organic matter, soil solution chemistry, abiotic adsorption, soil organic matter