Soil Fungi Respond More Strongly than Fine Roots to Elevated CO2 in a Model Regenerating Longleaf Pine-Wiregrass Ecosystem

Rising atmospheric CO₂ concentration will affect belowground processes and forest function. However, the direction and magnitude of change for many soil processes are unknown. We used minirhizotrons to observe fine root and fungal dynamics in response to elevated CO₂ in a model regenerating longleaf pine community in open-top chambers. The model community consisted of five plant species common to xeric sandhills longleaf pine stands: Pinus palustris, Quercus margaretta, Aristida stricta, Crotalaria rotundifolia, and Asclepias tuberosa. Elevated CO₂ significantly increased both fine root and mycorrhizal tip standing crop by more than 50% in the deeper soil horizon (17–34 cm). Rhizomorph standing crop was nearly doubled in both deep and shallow soil (P = 0.04). Survivorship results for fine roots and rhizomorphs varied between soil depths. Fine root survivorship was likely influenced more by changes in community composition and species interactions driven by elevated CO₂ rather than by direct effects of elevated CO₂ on the fine roots of individual species. In this system, it appears that elevated CO₂ led to a greater reliance on fungal symbionts to meet additional nutrient requirements rather than substantially increased root growth.