Effects of elevated atmospheric CO2 on root dynamics, biomass, and architecture in a scrub-oak ecosystem at Kennedy Space Center, Florida, USA

Large belowground structures and fine roots play an important role in carbon sequestration.  Non-destructive methods, ground-penetrating radar and minirhizotrons, were used to investigate effects of elevated CO₂ on root biomass, productivity, mortality, turnover, persistence, and architecture in a scrub-oak ecosystem in Florida.  Open-top chambers have been used to expose plants in ca 50 m² plots of scrub-oak to elevated atmospheric CO₂ for the past eleven years.  Minirhizotron data showed that there were no significant sustained CO₂ treatment effects on fine root length density, due to root closure.  Fine root density at lower soil depths increased to match abundance levels observed in the upper portions of the soil profile.  The smallest root size classes (<0.1 mm in diameter and <0.25 mm in length) were most susceptible to mortality, while root persistence increased with soil depth.  Ground-penetrating radar showed that greater coarse root biomass developed under elevated CO₂ exposure.  Overall, 86% of the total plant biomass was belowground with 78% of the belowground biomass allocated to coarse and 22% to fine roots.  Coarse root architecture determinations confirmed the abundance of large belowground structures in this system.  Large roots, especially those with distinct angles that transverse the study areas, were most likely to be identified in GPR architecture images.  Coarse roots play a large role in long-term carbon sequestration, thus having implications to carbon dynamics, treatment memory, and plant regeneration in a scrub ecosystem following a disturbance such as fire.