Type of Document Dissertation Author Prater, James Lee Author's Email Address email@example.com URN etd-11072005-233744 Title Metabolic Pathways in Natural Systems: A Tracer Study Degree Doctor of Philosophy Department Oceanography, Department of Advisory Committee
Advisor Name Title Chanton Committee Chair Burnett Committee Member Koska Committee Member Mortazavi Committee Member Wang Committee Member Winchester Committee Member Keywords
- Carbon Stable Isotopes Fractionation Respiration
Date of Defense 2005-09-16 Availability unrestricted AbstractThe ä13C value of foliage respiration has been considered a constant in the past and modeling efforts have assumed that the ä13C value of foliage respiration is constant and is directly related to substrate without any fractionation. Consecutive ä13C measurements of foliage dark-respired CO2 (ä13Cr) for slash pine trees (Pinus elliottii) over several diel cycles were used to test the hypothesis that significant variation in ä13Cr would be observed. ä13Cr values collected in daylight from all time series showed mid-day 13C enrichment (5 – 10‰) relative to bulk biomass, but values become more 13C depleted following shading and at night and approach bulk-biomass ä13C values by dawn. Assimilation model results suggest that respiration during daylight has the potential to significantly affect Ä13C by as much as 1.6‰, but night dark respiration has little impact on 24-hour integrated Ä13C (0.1‰).
We also sampled methane and CO2 from collapse scar bogs (transient permafrost degradation features in permafrost peatlands) to test the hypotheses that microbial respiration and methane production are stimulated by permafrost degradation and that the fen-like vegetation (i.e. Carex and Eriophorum) found in collapse scar bogs near the collapsing edge stimulates acetate fermentation. Our results show that collapse scar bogs have an evolution of spatial
variation in methanogenic pathways that is related to surface vegetation type. We also demonstrate that changes in stable-isotope fractionation caused by shifts from acetate fermentation and CO2 reduction occur over long time scales (> annual) and are dependent on changes in wetland morphology and surface vegetation cover.
Radiocarbon was also used as a tracer to test the hypothesis that melting permafrost provides nutrients that stimulates the production of radiocarbon-depleted methane. Our results show that the radiocarbon content of methane and DIC at these sites is highly variable and may depend on groundwater input, surface vegetation, and morphological factors associated with the melting permafrost plateau. We conclude that the younger, more labile, carbon stimulating acetate fermentation at one of the sites is supplied by the fen-like surface vegetation, while the older, more recalcitrant, carbon stimulating CO2 reduction at the other site may be supplied by melting permafrost plateau.
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