Turnover of soil C pools contributing to soil respiration in a forest exposed to elevated [CO2].
Taneva, Lina*,1, Pippen, Jeffrey2, Schlesinger, William2, Gonzalez-Meler, Miquel 1, 1 University of Illinois at Chicago, Chicago, IL2 Duke University, Durham, NC
ABSTRACT- Rising atmospheric [CO2] can potentially affect soil organic matter cycling in terrestrial ecosystems, with consequent feedbacks to the global C cycle. At the Duke Forest Free-Air CO2 Enrichment (FACE) experiment, previous studies have reported that net primary production is consistently enhanced by elevated [CO2]. Despite increased soil C inputs, significant C accumulation with elevated [CO2] has not been observed for any soil fraction and can only be detected in the forest floor of this ecosystem. We used the ecosystem 13C tracer from the fumigation CO2 to determine the turnover rate of the soil C pools contributing to soil CO2 and soil respiration in this forest. The rate of incorporation of labeled C into soil-respired CO2 and soil CO2 at 15-cm, 30-cm, 70-cm and 200-cm soil depth can be described by a model having 1-3 exponential isotope pools. From the changes in the isotopic signature of soil CO2 and soil-respired CO2, the contribution and turnover rate of these soil C pools can be determined. Our results suggest that the majority of soil CO2 is composed of C that is less than one year old. Such short ecosystem residence time of photosynthetic C may explain low observed rates of soil C accumulation.
Key words: elevated co2, soil c storage, c isotopes, soil c turnover
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