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Harvard Forest Symposium Abstract 2006
- Title: Interannual Variability of Carbon Isotope Ratios of Ecosystem Respiration in Harvard Forest between 2001-2005
- Primary Author: ChunTa Lai (San Diego State University)
- Additional Authors: Jim Ehleringer (University of Utah)
- Abstract:
The carbon isotope ratios of carbon dioxide fluxes from terrestrial ecosystems are key measurements needed to constrain interpretations of sinks in carbon cycle analyses. We have been measuring carbon isotope ratios of ecosystem respiration (d13CR) on weekly intervals in Harvard Forest since 2001. These long-term d13C observations have been extremely useful, revealing patterns that are clear on an interannual basis, but would not be evident with only a single year of measurements. The global atmospheric d13C value has been decreasing at a rate of ~ 0.02 ‰ year-1 as a result of the addition of fossil carbon that contains low 13C contents. Considering this decreasing rate of atmospheric d13C along, however, cannot explain the magnitude of changes in averaged d13CR values observed over 5 growing seasons in Harvard Forest (from -26.6 to -27.6 ‰, Table 1). It is likely that changes in ecosystem physiology and function, probably in response to global change (atmospheric CO2 fertilization, nitrogen deposition, energy partitioning and changes in precipitation amount and distribution), contribute to this substantial decrease in the d13CR vale at the ecosystem level. Whether this annual trend persists in coming years in Harvard Forest, or appears consistently in other ecosystems remain to be seen. Coincidentally, eddy covariance measurements showed enhanced rates of net carbon uptake (increased sink strength) in this forest over the last 5 years (Bill Munger, unpublished data). It is too early to conclude whether the correlation between d13CR and NEE trends is biologically meaningful. Yet, this question cannot be answered without continuous measurements of atmospheric d13C at AmeriFlux sites.
- Research Category: Forest-Atmosphere Exchange
Physiological Ecology, Population Dynamics, and Species Interactions
