ARS | Publication request: Soil Fungi Respond More Strongly Than Fine Roots to Elevated CO2 in a Model Regenerating Longleaf Pine-Wiregrass Ecosystem

Submitted to: Ecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 30, 2010
Publication Date: September 1, 2010
Citation: Mccormack, M.L., Pritchard, S.G., Breland, S., Davis, M.A., Prior, S.A., Runion, G.B., Mitchell, R.J., Rogers Jr, H.H. 2010. Soil fungi respond more strongly than fine roots to elevated CO2 in a model regenerating longleaf pine-wiregrass ecosystem. Ecosystems. 13:901-916.

Interpretive Summary: The level of carbon dioxide (CO2), a by-product of burning fossil fuels like gasoline and coal, continues to rise in the atmosphere. Trees, which absorb CO2, may be affected by these higher levels which may produce changes in their roots and other soil processes. We exposed a model young longleaf pine plant community to normal air and to air with twice the normal level of CO2. Fine roots (= 2 mm diameter), rhizomorphs (bundles of fungal hyphae), and mycorrhizal (a beneficial association of roots with fungi) were watched for 2 and a half years using minirhizotrons (glass tubes placed in the soil which a small camera can fit down). The community grown under high CO2 and more fine roots and doubled the number of mycorrhizal tips in the deeper soil horizon (7-14 in). Rhizomorph standing crop was nearly doubled in both deep and shallow soil. In our plant community, elevated CO2 led to a greater reliance on beneficial fungi to meet the additional nutrient requirements from larger growth rather than increasing root growth. The increases in both roots and beneficial fungi deeper in the soil might mean that these plant communities will store more of the carbon they remove from the atmosphere in the soil which could slow the rise in the CO2 level in the atmosphere.

Technical Abstract: Increasing atmospheric CO2 will have significant effects on belowground processes which will affect forest structure and function. A model regenerating longleaf pine-wiregrass community [consisting of longleaf pine (Pinus palustris), wiregrass (Aristida stricta), sand post oak (Quescus margaretta), rattlebox (Crotalaria rotundifolia), and butterfly weed (Asclipias tuberosa)] was grown under ambient (365 µl l-1) and elevated (720 µl l-1) CO2 in open top chambers. Fine root (= 2 mm diameter), rhizomorph, and mycorrhizal tip dynamics were recorded for 2.5 years using minirhizotrons. Elevated CO2 significantly increased fine root and doubled mycorrhizal tip standing crop in the deeper soil horizon (17-34 cm). Rhizomorph standing crop was nearly doubled in both deep and shallow soil. In this system it appears that elevated CO2 led to a greater reliance on fungal symbionts to meet additional nutrient requirement rather than substantially increased root growth. Overall, changes in the plant root and fungal communities resulting from elevated CO2 are likely to be equally or more important than the responses of individual species.