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.

Anabolic and catabolic contributions to total soil respiration.

Raich, James^*,1, ¹ Iowa State University, Ames, IA, U.S.A.

ABSTRACT- The results of numerous studies indicate that soil respiration rates are likely to increase in response to increases in atmospheric CO₂ and to increases in temperature. However, the effects of higher soil respiration rates on soil organic matter (SOM) pools are difficult to ascertain because soil respiration is a net flux that reflects changes in SOM decomposition and root respiration rates, both of which may respond to environmental changes. I review published data and present new data that was collected to distinguish belowground autotrophic (root) and heterotrophic (microbial) contributions to the total soil CO₂ efflux. Isotopic data, in particular, have shown promise of allowing these two main CO₂-producing processes to be individually quantified, in sites that have recently been subject to a change in vegetation cover. What evidence exists, though, for the remaining 99% of the world's land surface? I suggest that the classic distinction between autotrophic and heterotrophic sources of CO₂ in soils needs to be modified to better understand belowground C-cycling processes, and propose a conceptual model that is consistent with existing data, and which allows for the estimation of anabolic and catabolic contributions to the total soil-CO₂ efflux. Such an approach would greatly enhance our capacity to interpret the results of experimental studies, and to evaluate the potential responses of terrestrial ecosystems to changing environmental conditions.

Key words: soil carbon budgets, carbon cycle modeling, root dynamics, decomposition