Friday, August 10, 2007: 9:50 AM
J3, San Jose McEnery Convention Center
Theodore K. Raab, Stanford University, Stanford, CA, Jason C. Neff, Environmental Studies Program and Geosciences Department, University of Colorado, Boulder, CO, Marc Kramer, Earth and Planetary Sciences, University of California, Santa Cruz, CA, Reinhard Jetter, Depts. of Botany and Chemistry, University of British Columbia, Vancouver, BC, Canada and Peter M. Vitousek, Department of Biology, Stanford University, Stanford, CA
Chemistry of plant material is a crucial control on litter decomposition rates. However, we know less about the fate of plant-derived compounds entering soils. A variety of mechanisms stabilize (or destabilize) plant litter in soil. Despite lignin dominance as a structural control in litter decomposition, other plant compounds such as epicuticular waxes may be more important in soils. Employing several analytical methods (FT-infrared spectromicroscopy, flash-pyrolytic gas chromatography-mass spectrometry, and 13C-nuclear magnetic resonance), we examined plant-soil chemistry over a range of decomposition. We examined: (1) live foliage and fresh litter from a fast-decomposing tree in the Araliaceae (Cheirodendron trigynum), and a slow-decomposing Gleicheniales fern (Dicranopteris linearis); (2) litter differing in mass loss % from decomposition experiments; (3) root mats below stands of certain species; and (4) size fractions of O- and A- soil horizons from 3-ky and 150-ky Hawai`ian sites. PyGC-MS comparisons of foliage and litter indicate fatty acid methylesters distinguish the slow-decomposing fern from fast-decomposing tree. We removed epicuticular wax from the two species for GC-MS. Not only is the wax / wax-ester load much higher in fern than the tree, but novel secondary waxy alcohols / diols were detected in fern cuticles. Remaining tissues yielded significantly different FT-IR signals from polysaccharides and cell wall-phenolics, with preferential preservation of polysaccharides in the fern, and lipids in the tree. In the field, py-GCMS suggests plant composition plays a role in controlling soil chemistry, tending towards higher concentrations of lipid derived materials in soils under vegetation with high fatty acid content.
