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.

Influence of elevated atmospheric CO₂ on root biomass accumulation in Florida oak-scrub.

Pagel, Alisha^*,1, Day, Frank¹, Hungate, Bruce², Drake, Bert³, ¹ Old Dominion University, Norfolk, VA² Northern Arizona University, Flagstaff, AZ³ Smithsonian Environmental Research Center, Edgewater, MD

ABSTRACT- During the first two years after fire disturbance, continuous minirhizotron observations revealed that elevated atmospheric CO₂ stimulated fine root abundance in a scrub-oak woodland in central Florida. During years 5-6, however, fine root abundance converged in the two CO₂ treatments. To confirm these findings and to develop relationships between root biomass and the minirhizotron observations, we removed soil cores (7 cm diameter by 1 m deep) from each experimental chamber six years after CO₂ manipulation began. Live roots, dead roots and organic matter were separated from the soil, and live roots were sorted into five diameter classes. Similar to recent trends observed in the minirhizotron data, preliminary core data suggest that elevated CO₂ altered neither root biomass or root length. Specific root lengths also did not appear to differ between ambient and elevated CO₂ treatments for the smaller diameter classes, but for the 2-10 mm roots, the specific root length of elevated CO₂-grown roots was 20% greater than roots grown in ambient conditions. Elevated CO₂ initially stimulated root growth in this ecosystem, but the effect appears to be transient, disappearing after 3-5 years possibly as CO₂ treatments converge on closure of the root system.

Key words: Roots, Elevated CO2, Minirhizotron