Monday, November 13, 2006 - 1:45 PM

Above- and Below-Ground Litter Controls on Forest Soil Dynamics.

Kate Lajtha1, Susan Crow2, Bruce Caldwell3, Yuriko Yano1, Elizabeth Sulzman1, and Phil Sollins1. (1) Oregon State Univ, Dept Botany and Plant Pathology, Corvallis, OR 97331, (2) Purdue Univ, EAS Dept, 550 Stadium Mall Dr, West Lafayette, IN 47907, (3) Oregon State Univ, Dept of Forest Science, 321 Rich Hall, Corvallis, OR 97331-5752

Forests play a key role in the global C cycle, sequestering atmospheric C within SOM and wood.  However, interactions among biological and chemical-physical processes regulating gains and losses of SOM in forests are poorly understood.  We established a long-term field study in a coniferous forest at the H.J. Andrews Experimental Forest, OR, USA, to address how detrital quality and quantity control SOM accumulation and stabilization. The Detritus Input and Removal Treatments (DIRT) plots consist of treatments that double leaf litter, double woody debris, exclude litter, or remove root inputs. The addition of woody debris increased DOC concentrations in O-horizon leachate and at 30 cm, but not at 100 cm, compared to control plots, suggesting increased DOC retention with added woody debris. DOC concentrations decreased through the soil profile in all plots to a greater degree than did DON, most likely due to preferential sorption of high C:N hydrophobic DOM in upper horizons. Although laboratory extracts of different litter types showed differences in DOM chemistry, percent hydrophobic DOM did not differ among soil solutions from different detrital treatments in the field, suggesting that microbial processing of DOM leachate in the field consumed easily degradable components, thus equalizing leachate chemistry among treatments.  In plots without roots, N losses were less than half of estimated plant uptake, suggesting that other mechanisms, such as increased microbial immobilization, accounted for retention of N in deep soils. In long-term laboratory incubations, soils from plots that had both above- and below-ground litter inputs excluded showed a trend towards lower DOC loss rates, but not lower respiration rates. Soils from plots with added wood had similar respiration and DOC loss rates as control soils, suggesting that the additional DOC sorption observed in the field in these soils was stabilized in the soil and not readily lost upon incubation.