HR: 1340h
AN: B23C-1501    [Abstracts]
TI: Scrub-Oak Biomass Stimulation by CO2 Enrichment: Sustained 11 Years But Mediated by Precipitation and Contrasting Species Responses
AU: Seiler, T
AF: Smithsonian Environmental Smithsonian Environmental Research Center, PO Box 28, Edgewater, MD 21037, United States
AU: Li, J
AF: Smithsonian Environmental Smithsonian Environmental Research Center, PO Box 28, Edgewater, MD 21037, United States
AU: Dijkstra, P
AF: Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011, United States
AU: Anderson, H
AF: Smithsonian Environmental Smithsonian Environmental Research Center, PO Box 28, Edgewater, MD 21037, United States
AU: Johnson, D
AF: Smithsonian Environmental Smithsonian Environmental Research Center, PO Box 28, Edgewater, MD 21037, United States
AU: Hinkle, R
AF: Department of Biology, University of Central Florida, Orlando, FL 32816, United States
AU: * Drake, B
AF: Smithsonian Environmental Smithsonian Environmental Research Center, PO Box 28, Edgewater, MD 21037, United States
AB: Terrestrial ecosystems may mitigate rising atmospheric carbon dioxide concentration (CO2) through increased carbon uptake and sequestration in plant biomass. Elevated CO2 commonly produces initial stimulation of photosynthesis and growth, but due primarily to complex interactions with climate related factors (i.e. water, light and nutrients), uncertainty regarding long-term biomass response persists. After 11 years of CO2 enrichment (ambient and ambient + 350 ppm) using open-top chambers, aboveground biomass stimulation was sustained in a Florida scrub-oak ecosystem, yielding a 67% increase at final harvest in June 2007. The scrub oaks Quercus geminata and Quercus myrtifolia represented 85% of total ecosystem aboveground biomass but displayed contrasting responses to elevated CO2. Q. myrtifolia showed consistent increase in shoot biomass over the course of the study (128% stimulation by elevated CO2) while shoot biomass of Q. geminata was not significantly increased (+6% difference between treatments). Both species displayed long-term mean stimulation of net leaf photosynthesis to elevated CO2 under saturated light conditions: stimulation of photosynthesis in Q. myrtifolia was nearly twice that in Q. geminata (63% and 35%, respectively). Over the course of the study, Q. geminata consistently displayed photosynthetic acclimation via reductions in maximum carboxylation rate (Vcmax) and maximum rate of electron transport (Jmax) while Q. myrtifolia photosynthesis did not acclimate to elevated CO2. Inter-annual variation in Q. myrtifolia annual biomass increment was correlated with rainfall and elevated CO2 stimulation of absolute biomass accumulation was greatest in wet years. This effect was muted at the ecosystem level because CO2 stimulation of biomass in Q. geminata, which utilizes the water table to a greater extent than Q. myrtifolia, showed no relationship with rainfall. These advantages afforded to Q. myrtifolia by elevated CO2 produced a significant change in ecosystem composition, a trend which may be further compounded over time by this system's short fire return cycle.
DE: 0410 Biodiversity
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting