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Carbon dioxide exchange over an evolving successional landscape.
Emanuel, Ryan1, Albertson, John2, Epstein, Howard*,1, D'Odorico, Paolo1, Williams, Christopher2, 1 University of Virginia, Charlottesville, VA2 Duke University, Durham, NC
ABSTRACT- Successional ecosystems are believed to be significant sinks of atmospheric carbon dioxide. In order to explore the mechanisms of carbon sequestration over successional timescales, an eddy covariance system was installed above a crop field at the Blandy Experimental Farm in Virginia, USA in January 2001. Half-hourly fluxes of carbon dioxide and water vapor, and state variables such as soil temperature and soil moisture were measured continuously through one season of crop growth and the period of succession following harvest of that crop. Here we report the results of the first year of successional growth in the absence of cultivation. Despite primary production on the order of 1 kg m-2 during the first full year of succession, this ecosystem remains a net source of carbon dioxide to the atmosphere. To investigate this phenomenon, a process-based model of ecosystem respiration was developed using nighttime eddy covariance measurements partitioned into bins based on soil moisture and vegetative structure, and evaluating nighttime flux in each bin as an exponential function of soil temperature. Output from the model was compared with concurrent ground-based measurements of ANPP and soil respiration. Our model implies that ecosystem respiration exceeds photosynthetic uptake in this early stage of succession, and demonstrates mechanistically the means by which carbon flux is controlled by soil moisture, soil temperature and vegetative structure at hourly to seasonal scales.
Key words: ecosystem respiration, net ecosystem exchange, succession, eddy covariance