In 1996, a long-term CO2 enrichment study was initiated in a scrub-oak ecosystem at Kennedy Space Center, Florida. The experimental design involved 16 open-top chambers that continuously received either ambient or elevated (ambient + 350 ppm) CO2 concentrations. The objective of the work presented here was to determine the effect of elevated CO2 on fine (<5 mm diameter) and coarse (>5 mm diameter) root biomass in this system. Fine root abundance within the experimental chambers was measured throughout the study using minirhizotrons. Biomass of fine roots was estimated from mass/root length values applied to the minirhizotron data. To measure coarse root biomass, ground-penetrating radar (GPR) was used at the end of the study in May 2007, after CO2 enrichment was stopped and all aboveground vegetation within the experimental plots was removed.
Results/Conclusions
Measurements of root length density (RLD) of fine roots showed stimulation under elevated CO2 during the early years of the experiment but no effect by the end. Fine root biomass was significantly greater under elevated CO2 for 8 out of 23 sampling dates between 1996 and 2006. Coarse root biomass estimates were 6,040 ± 507 g m-2 for the elevated CO2 plots and 5,105 ± 418 g m-2 for the ambient CO2 plots. Overall, 11 years of exposure to elevated atmospheric CO2 stimulated production of root biomass. This ecosystem experiences periodic fires, and belowground carbon reserves (i.e. coarse roots, lignotubers, and burls) are important for plant re-growth following disturbance. Total root biomass was found to be 4-6 times greater than aboveground biomass in this system, suggesting that as CO2 increases, additional carbon sequestered from the atmosphere may be stored in belowground plant structures.
