Photosynthetic Carbon Isotope Discrimination Increases with Elevated CO2 in a Grassland Ecosystem

Thursday, 18 December 2014
Tamara Jane Zelikova, University of Wyoming Libraries, Laramie, WY, United States, Elise Pendall, University of Western Sydney, Penrith, NSW, Australia, David G Williams, University of Wyoming, Laramie, WY, United States and Dan R LeCain, United States Department of Agriculture, Agricultural Research Service, Rangeland Resources Research Unit, CO, United States
Paleoecological reconstructions and land-surface ecosystem models assume that as atmospheric CO2 changes, photosynthetic carbon isotope discrimination and the ratio of leaf internal to ambient CO2 concentration (ci/ca) remains unchanged, but this assumption has rarely been tested. Atmospheric CO2 concentrations are expected to rise to at least 600ppm by the end of the 21st century, with global temperatures and precipitation regimes concurrently changing and interacting to influence plant photosynthetic gas exchange. In the PHACE (Prairie Heating and CO2 Enrichment) experiment, we examined the influence of elevated CO2, warming, and summer irrigation on carbon isotope discrimination among C3 and C4 graminoid and dicot species to understand species and ecosystem responses to over 7 years of experimental climate change. Carbon isotope discrimination increased for all species when exposed to elevated CO2, but this effect did not emerge until the third year of the experiment. In addition, though species inherently differed in their carbon isotope discrimination, their ranking remained stable under elevated CO2. Quantifying the relative importance of factors that influence plant carbon isotope discrimination can guide our understanding of how individual plant species, plant communities, and ecosystems may react to global change. Evidence that plant carbon isotope discrimination shifts with changes in atmospheric CO2 and temperature has important implications for interpretation of the paleo record from archival organic materials and for modeling carbon cycling processes in future environments.