Wednesday, November 7, 2007 - 3:50 PM
290-12
Biogeochemical Controls Over C Structure: Implications for C Stabilization in Disturbed Ecosystems.
A. Stuart Grandy1, Jason C. Neff2, and Catherine Stewart2. (1) Crop and Soil Sciences, Michigan State University, East Lansing, MI 48824, (2) Geological Sciences, University of Colorado, Boulder, CO 80309
The molecular structure of soil organic matter has been determined in many ecosystems but the controls over C chemistry remain uncertain. Differences in plant chemistry are one source of variation and we show that vegetation influences the structure of young, coarse soil organic matter more strongly than the chemistry of older, microbially processed pools. These older pools, which usually constitute the majority of soil organic matter, have C fingerprints that reflect complex interactions between plant inputs, climate, geochemistry, and soil biological communities. Comparisons across sites in Colorado , Michigan, and Hawaii show somewhat predictable changes in C chemistry across horizons and soil fractions due to decomposition and changes in organo-mineral interactions. In volcanic soils from Hawaii with different types of vegetation, phenols consistently decrease from the O- (~50% relative abundance) to the A-horizon (~25%), likely reflecting the decline of lignin-derived C. Across size fractions, we show in soils from the Manistee National Forest, MI and the San Juan Mountains, CO that polysaccharides and lipids frequently double in abundance going from coarse to fine fractions and that this is associated with declines in lignin-derived compounds. In Hawaii, though, changes in C structure across size fractions seem to vary with vegetation, indicating a potential interaction between plant inputs and the biogeochemical controls over decomposition. Understanding these interactions, as well as the effects of land use change, climate variability and other disturbances requires a better understanding of soil biological processes and their effects on C chemistry. Our work shows that declines in oxidase enzymes following N enrichment as well as saturated soil conditions can alter lignin turnover and C stabilization. Others have shown that soil fauna such as earthworms can influence C structure and that different microbial groups have unique structures. Collectively, these studies suggest that there are general patterns in the effect of microorganisms, vegetation and mineralogy on soil organic matter structure that can be modified by human activities.