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Title: Warming reduces carbon losses from grassland exposed to elevated atmospheric carbon dioxide

Author
item PENDALL, ELISE - University Of Sydney
item HEISLER-WHITE, JANA - University Of Wyoming
item WILLIAMS, DAVID - University Of Wyoming
item DIJKSTRA, FEIKE - University Of Sydney
item CARRILLO, YOLIMA - University Of Sydney
item MORGAN, JACK - Retired ARS Employee
item Lecain, Daniel

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/3/2013
Publication Date: 8/19/2013
Citation: Pendall, E., Heisler-White, J., Williams, D., Dijkstra, F., Carrillo, Y., Morgan, J.A., Lecain, D.R. 2013. Warming reduces carbon losses from grassland exposed to elevated atmospheric carbon dioxide. PLoS One. 8(8):e71921. DOI:10.1371/journal.pone.0071921.

Interpretive Summary: Mixed grass prairie in Wyoming was exposed for 8 years to increased atmospheric carbon dioxide concentrations and warming (higher temperatures), at levels predicted to occur by the end of this century. One of the key questions for this native grassland is how the predicted global changes may influence the carbon balance. We found that carbon lost from the plants and soils due to respiration was greater than the carbon gained by plants through photosynthesis with increased atmospheric carbon dioxide concentrations alone or in combination with warming.

Technical Abstract: The flux of carbon dioxide (CO2) between terrestrial ecosystems and the atmosphere may ameliorate or exacerbate climate change, depending on the relative responses of ecosystem photosynthesis and respiration to warming temperatures, rising atmospheric CO2, and altered precipitation. The combined effect of these global change factors is especially uncertain because of their potential for interactions and indirectly mediated conditions such as soil moisture. Here, we present observations of CO2 fluxes from a multi-factor experiment in semi-arid grassland that suggests a potentially strong climate – carbon cycle feedback under combined elevated [CO2] and warming. Elevated [CO2] alone, and in combination with warming, enhanced ecosystem respiration to a greater extent than photosynthesis, resulting in net C loss over four years. The effect of warming was to reduce respiration especially during years of below-average precipitation, by partially offsetting the effect of elevated [CO2] on soil moisture and C cycling. Carbon losses were explained partly by stimulated decomposition of soil organic matter with elevated [CO2]. The climate – carbon cycle feedback observed in this semiarid grassland was mediated by soil water content, which was reduced by warming and increased by elevated [CO2]. Ecosystem models should incorporate direct and indirect effects of climate change on soil water content in order to accurately predict terrestrial feedbacks and long-term storage of C in soil.