A scrub-oak ecosystem at Kennedy Space Center, Florida was exposed to 11 years of atmospheric CO2 enrichment (ambient + 350 ppm) using open-top chambers. The objective of our study was to determine the effect of elevated CO2 on fine roots < 2 mm diameter using minirhizotrons and on coarse roots > 5 mm diameter using ground-penetrating radar (GPR). Fine root measurements of root length density (RLD) were applied to specific root length values to calculate fine root biomass to a depth of 100 cm. GPR data were applied to previously-established relationships between GPR signal reflectance and root biomass to estimate coarse root biomass to a depth of 60 cm. 3-dimensional GPR data imaging was also used to assess root architecture and depth distributions.
Results/Conclusions
Total root biomass after 11 years of CO2 enrichment was not greater in elevated plots (7670 ± 467 g/m2) than in ambient plots (6655 ± 399 g/m2; P = 0.1208). Coarse roots comprised 76% and 77% of root biomass for elevated and ambient plots, respectively. Root-to-shoot ratios were 3.9 for elevated and 5.5 for ambient CO2 plots, demonstrating that root biomass contributes the most to total plant biomass in this system. Belowground plant structures in this fire-dominated system sequester substantial carbon from the atmosphere and provide an important sink for atmospheric CO2. Under elevated CO2, depth distribution of root biomass was affected, with an increase in biomass at 10-50 cm depth compared to a decrease of biomass with increasing depth in ambient CO2 plots.