PARENT SESSION

Symposium S1D Photosynthesis and global change
Monday August 30th, 2004 10:20 AM-12:20 PM Room 510B
Chair: Dave Layzell and Neil Baker
Co-Chair: Don Ort

The changing role of forests in the global carbon cycle: responses to elevated atmospheric CO₂. Evan DeLucia^*,1, David Moore², Jason Hamilton³, Adrien Finzi⁴, Jeff Pippen⁵, William Schlesinger⁵, Richard Norby⁶, ¹ Department of Plant Biology, Urbana, IL, USA² Program in Ecology and Evolutionary Biology, Urbana, IL, USA³ Department of Biology, Ithaca, NY, USA⁴ Department of Biology, Boston, MA, USA⁵ Nicholas School of the Environment and Earth Sciences, Durham, NC, USA⁶ Environmental Sciences Division, Oak Ridge, TN, USA

ABSTRACT- The combustion of fossil fuels is injecting vast quantities of CO₂ into the atmosphere, altering the C cycle in ecosystems and driving an increase in global temperatures. Forests contribute half or more of global net primary production and approximately 80% of terrestrial productivity and thus play a central role in the global carbon cycle. Using free-air CO₂ enrichment technology to expose plots within intact forests to the level of CO₂ anticipated in 2050, it was discovered that net ecosystem productivity (NEP) and net primary productivity (NPP) in loblolly pine and sweetgum forests were substantially increased. The stimulation in the pine forest was greater in warm years than in cool years. Greater plant respiration contributed to lower NPP in the sweetgum than in the pine forest. These forests responded differently to elevated CO₂. Where the pine forest added C to woody tissues, exposure to elevated CO₂ caused a large increase in fine root production in the sweetgum forest. Differences in allocation may alter the mean residence time of C in different forests. As these forest age, imbalances in the N cycle may reduce the response of these forests to elevated CO₂. The stimulation of forest productivity has the potential to slow the accumulation of CO₂ in the atmosphere, but if these forests are representative of forests globally, the observed stimulation of productivity is insufficient to reverse the accumulation fossil-fuel derived C in the atmosphere.

KEY WORDS: elevated CO₂, global change, productivity, forests