PARENT SESSION
Symposium 14: Respiratory Control of the Global C Cycle in a Changing Environment
Organized by: M Gonzalez-Meler and W Schlesinger
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Chatham Ballroom B.

Sources of soil respiration determined using radiocarbon.

Trumbore, Susan ^*,1, Gaudinski, Julia ², Davidson, Eric ³, Cisneros Dozal, Luz Maria¹, Camargo, Plinio⁴, Schuur, Edward⁵, Chambers, Jeffrey¹, ¹ University of California-Irvine, Irvine, CA² University of California-Santa Cruz, Santa Cruz, CA³ The Woods Hole Research Center, Woods Hole, MA⁴ Centro de Energia Nuclear na Agricultura, Piracicaba, Sao Paulo, Brazil⁵ University of Florida-Gainseville, Gainseville, FL

ABSTRACT- Soil respiration combines CO₂ derived from autotrophic (root metabolism) and heterotrophic (organic matter decomposition) sources. A major challenge in ecological research is to determine how much of soil respiration comes from each of these sources, and how each may respond to environmental changes. We have developed methods using the difference in radiocarbon among these substrates to quantify these sources, and in addition to determine the relative contribution of different decomposing substrates to overall heterotrophic C losses. This talk will present radiocarbon measurements of soil respiration and its components from tropical, temperate and boreal ecosystems, as well as discuss how temperature and moisture can influence the different components of soil respiration. Radiocarbon in microbially-respired CO₂ provides a measure of the mean residence time of fast-cycling C pools in ecosystems, which vary from several years in tropical systems to decades in boreal forests. In contrast, soil organic matter is often comprised of more stable, slowly cycling components that contribute little to soil respiration. The pools contributing the most to heterotrophic respiration include leaf and root litter; in particular soil respiration rates can be sensitive to the moisture content of the leaf litter layer. More stable, humified, organic matter pools contribute little to respired C on an annual basis, but are important for C balance on longer (decades-centuries) time scales.

Key words: soil respiration, radiocarbon, carbon cycle, soil carbon