Monday, November 13, 2006

Different Input Sources Dominate Soil Organic Matter Dynamics at 2 Forested Sites (DIRT Project).

Susan E. Crow1, Timothy R. Filley1, Bruce A. Caldwell2, and Kate Lajtha3. (1) Purdue Univ, EAS Dept, 550 Stadium Mall Dr., West Lafayette, IN 47907, (2) Oregon State Univ, Dept of Forest Science, Corvallis, OR 97331-5752, (3) Oregon State Univ, Dept Botany and Plant Pathology, Corvallis, OR 97331

Changes in land use or climate can alter the quantity and quality of detrital inputs to the forest floor, which may translate into changes in soil organic matter (SOM) accumulation and stabilization over time. Mineral soils and litter from on-going litter input manipulation treatments at 2 forested sites, a coniferous western hemlock/Douglas-fir stand on andic soils in Oregon (since 1997) and a mixed-deciduous stand on Alfisols in western Pennsylvania (since 1991), were investigated to determine the link between detrital inputs and SOM response.

The composition and concentration of CuO-extractable lignin phenols and substituted fatty acids (SFAs) were used to track plant biopolymer dynamics between detrital inputs, from either roots or aboveground sources, and the surface mineral soil (0-5 cm). Residual soil SFAs in the coniferous site were dominated by needle-derived cutin regardless of the detrital manipulations. In contrast, SOM SFAs indicate that both cutin-foliar and suberin-root material exert influence on SOM character within the deciduous site; however, roots exerted more influence under litter removal treatments while leaves had greater influence on SOM under doubled litter treatments. Root inputs dominate the lignin composition of the coniferous soil while no single source dominated lignin composition of the deciduous soil. Density fractionation of the mineral soil revealed the greatest amount of light fraction material (<1.6 g cm-3) in the soil with roots removed at the deciduous site and in the soil with doubled needles at the coniferous site. In both cases, these soil treatments also resulted in the least cumulative respiration from bulk soils during a one year incubation study, indicating that the OM accumulating as light fraction may be resistant to decomposition.