Poster Session # 13: Biogeochemistry, Photosynthesis, and Respiration.

Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Effects of elevated CO2 on root turnover and mortality in a Florida oak-scrub ecosystem.

Stover, Daniel*,1, Day, Frank1, Dilustro, John2, Drake, Bert3, 1 Old Dominion University, Norfolk, VA2 Savannah River Ecological Laboratory, Aiken, SC3 Smithsonian Environmental Research Center, Edgewater, MD

ABSTRACT- Fine root dynamics, such as mortality and turnover, influence sequestration of carbon in the soil. Measurements of the effects of elevated CO2 on fine root dynamics were conducted in an oak-scrub ecosystem at Kennedy Space Center, Florida. Minirhizotron tubes were utilized within ambient (350 ppm) and elevated (700 ppm) open top chambers along with reference controls. Fine root productivity, mortality and turnover were analyzed and compared to results five years earlier. In the second year of the study, CO2 enrichment resulted in higher fine root turnover (0.0266 compared to 0.0175 fractional root loss/day in the ambient), higher root production (0.0939 compared to 0.0524 mm/cm/day in the ambient) and higher mortality (0.0574 compared to 0.0231 mm/cm/day in the ambient). The effect of elevated CO2 on fine root abundance was reduced to non-significant levels after seven years of treatment. Preliminary evaluations of mortality and turnover in the seventh year of the study have yielded inconclusive results to date with regard to CO2 treatment effect. Disappearance of all treatment effects would suggest convergence of fine root systems among treatments, but similar root abundance in ambient and elevated could be masking higher turnover rates of fine roots in elevated chambers.

Key words: Minirhizotron, Root Turnover, CO2