Do mid-day carbon and water exchange differ from integrated values in four old-field species under global climate change?
Souza, Lara*,1, Nagel, Jennifer1, Engel, Elizabeth1, Weltzin, Jake1, Norby, Rich2, 1 University of Tennessee, Knoxville2 Oak Ridge National Laboratory, Knoxville, TN
ABSTRACT- Increasing concentrations of carbon dioxide [CO2] coupled with increases in global temperatures and changes in precipitation events are likely to impact plant community structure and physiological processes, such as the exchange of carbon and water. Studies in the past have mainly focused on one or two climatic factors, particularly on the responses of vegetation to CO2. To improve our understanding of global climate change on biological systems, we investigated the interactive effects of CO2, temperature, and soil water availability on a constructed old-field ecosystem, including C3, C4, and nitrogen-fixing plant functional types near Oak Ridge, Tennessee. Leaf-level gas exchange measurements were performed inside 4-m diameter open-top chambers four times during the growing season. We estimated daily leaf-level carbon and water exchange of two community dominant species (Trifolium pratense and Dactylis glomerata), as well as two community subordinate species (Plantago lanceolata and Solidago canadensis). We then compared integrated daily values of carbon assimilation and transpiration to mid-day responses. Preliminary data suggests that integrated values of carbon exchange for all species had a greater response to elevated CO2 compared to mid-day values. In turn, integrated values of transpiration were similar to mid-day values, regarding response to water and CO2 treatments for all four species.
Key words: carbon assimilation, transpiration, global change, old-field community
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