PARENT SESSION
Oral Session # 12: Biogeochemistry I: Carbon Dioxide Cycling.
Presiding: D Markewitz
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 204.
Effects of elevated CO2 on microbial respiration in a Florida scrub oak ecosystem.
Wolf, Amelia*,1, Megonigal, Patrick1, Hungate, Bruce2, Day, Frank3, Drake, Bert1, 1 Smithsonian Environmental Research Center, Edgewater, MD2 Northern Arizona University, Flagstaff, AZ3 Old Dominion University, Norfolk, VA
ABSTRACT- We measured microbial respiration over soil depth profiles in order to examine the effects of elevated CO2 on the soil labile C pool in a Florida scrub oak ecosystem. The study consisted of replicated (n=8) open-top chambers exposed to ambient or twice-ambient atmospheric [CO2], as well as non-chambered control plots. Triplicate 1-m deep cores were taken from each chambered plot and 1 core was taken from each non-chambered plot. Microbial respiration was measured at 4 depth intervals in a laboratory incubation over a 32-week period. Microbial respiration at the soil surface (0-10 cm) was consistently higher by 7-19% in the ambient chambers than in the elevated chambers, though this difference was not statistically significant. Previous studies have either observed a significant stimulation of microbial respiration by elevated CO2, or a non-significant trend for such an effect. At depths of 10-30 cm and 30-60 cm, elevated CO2 had no effect; however, when a spodic horizon (60-90 cm) was present, there was a trend of higher rates of microbial respiration in the elevated CO2 plots. Soils at all depths from the elevated chambers were significantly more depleted in 13C-CO2 than soils from ambient chambers and non-chambered plots, reflecting the highly depleted 13C content of the CO2 added to the elevated chambers. Collectively, these data lead us to speculate that elevated CO2 has stimulated the transport of labile soil carbon from the soil surface to deeper horizons, perhaps by reducing transpiration.
Key words: microbial respiration, Elevated CO2, stable isotope, scrub oak