PARENT SESSION
Contributed Oral Session 155: Biogeochemistry: Soil Carbon Dynamics
Friday, August 12, 8:00 AM - 11:30 AM, Meeting Room 516 A, Level 5, Palais des congrès de Montréal

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