HR: 1340h
AN: B23D-1614    [Abstracts]
TI: Changes in Soil Carbon and Nitrogen in a Multi-factor Climate Change Experiment on Constructed Old-Fields
AU: * Garten, C T
EM: gartenctjr@ornl.gov
AF: Oak Ridge National Laboratory, Environmental Sciences Division PO Box 2008, Oak Ridge, TN 37831, United States
AU: Classen, A T
EM: classenat@ornl.gov
AF: Oak Ridge National Laboratory, Environmental Sciences Division PO Box 2008, Oak Ridge, TN 37831, United States
AU: Norby, R J
EM: norbyrj@ornl.gov
AF: Oak Ridge National Laboratory, Environmental Sciences Division PO Box 2008, Oak Ridge, TN 37831, United States
AB: Single factor experiments indicate elevated CO₂ concentrations increase soil C stocks, but relatively few experiments have examined the effects of interacting environmental factors on soil C dynamics. We undertook studies in a multi-factor (CO₂ x temperature x moisture) experiment in east Tennessee to better understand the effects of these factors and their interactions on soil C and N in a constructed old-field community that included 7 species (including two N-fixers). Symbiotic N-fixation was an important process supplying N to Lespedeza cuneata, an invasive legume that dominated the communities after 3 years of treatments. Following four growing seasons, elevated CO₂ had no measurable effect on C and N concentrations in whole soils, particulate organic matter (POM), and mineral-associated organic matter (MOM). There were no statistically significant interactions involving CO₂ x temperature, CO₂ x water, or CO₂ x temperature x water. Soil moisture was the main factor affecting soil C and N following 4 years of treatments. Analysis of stable C isotopes indicated that the fraction of new C increased significantly in whole soils, POM, and MOM, and that the greatest gains (50% new C) were measured in POM under elevated soil moisture. Despite high rates of N- fixation and significant belowground inputs of new soil organic matter, soil C and N concentrations and C stocks in POM declined significantly over 4 years under conditions of higher soil moisture. Higher soil moisture increased soil respiration and calculated turnover times indicated overall faster soil C cycling under elevated soil moisture in the elevated CO₂ treatment plots. Higher soil moisture accelerated heterotrophic decomposition of labile soil organic matter more than it increased soil C inputs under elevated CO₂. The imbalance produced a net decline in soil C stocks and a widening of soil C/N ratios. POM was the most sensitive pool for detecting rapid changes in soil C in response to environmental change. Rapid loss of POM C, and associated declines in soil quality, would tend to promote long-term changes in plant community composition by favoring invasive N-fixers, like Lespedeza cuneata.
DE: 0428 Carbon cycling (4806)
DE: 0486 Soils/pedology (1865)
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting