Runion, G. Brett (USDA-ARSUSDA-ARS, NSDL, 411 S. Donahue Drive, Auburn, AL, 36832; Phone: 334-844-4517; Fax: 334-887-8597; Email:


Effects of Elevated Atmospheric CO2 on Biomass and Carbon Accumulation in a Model Regenerating Longleaf Pine Ecosystem


G.B. Runion*, M.A. Davis, S.G. Pritchard, S.A. Prior, R.J. Mitchell, H.A. Torbert, H.H. Rogers, R.R. Dute


Community response to elevated CO2 was examined in a model regenerating longleaf pine ecosystem exposed to two CO2 regimes (ambient, 365 ėmol mol-1 and elevated, 720 ėmol mol-2) for three years using open-topped chambers.  Total aboveground and belowground biomass was 70% and 49% greater, respectively, in CO2-enriched chambers; carbon (C) content followed a similar CO2 response pattern which resulted in a significant increase of 12.2 Mg C ha-1 sequestered in standing biomass, with an additional increase of 1.6 Mg C ha-1 in litter.  Responses of individual species, however, varied.  Longleaf pine (Pinus palustris) was primarily responsible for the positive response to CO2 enrichment (88%).  Wiregrass (Aristida stricta), rattlebox (Crotalaria rotundifolia), and butterfly weed (Asclepias tuberosa) all exhibited negative aboveground (-26%, -53%, and -65%, respectively) and belowground (-36%, -43%, and -52%, respectively) biomass responses to elevated CO2; C content responses again followed patterns similar to biomass.  While sand post oak (Quercus margaretta) had positive responses to CO2 enrichment (39% and 12% for above- and belowground, respectively), these did not differ significantly between treatments due to high variability.  Elevated CO2 resulted in alterations in community structure; 88% of total biomass in CO2-enriched plots was allocated to longleaf pine with only 8% allocated to wiregrass, rattlebox, and butterfly weed.  In comparison, ambient CO2 plots allocated only 76% of total biomass to longleaf pine but had 19% allocated to wiregrass, rattlebox, and butterfly weed.  Therefore, while longleaf pine may perform well in a high CO2 world, other members of this community may not be able to compete as well as atmospheric CO2 concentration continues to rise.  Regardless of individual species response, the entire system gained 11.4 Mg C ha-1 under elevated CO2 suggesting that this ecosystem should be a sink for atmospheric CO2.