Submitted to: Grassland International Congress
Publication Type: Abstract Only
Publication Acceptance Date: 1/1/2008
Publication Date: 6/11/2008
Citation: Morgan, J.A., Pendall, E., Williams, D.G., Lecain, D.R., Blumenthal, D.M., Dijkstra, F.A., Miglietta, F., Kimball, B.A. 2008. Plant productivity responses to rising atmospheric CO2 and warming in semi-arid grassland in Wyoming, USA. In: Proceedings of the Grassland International Congress/International Rangeland Congress. p. 895. Interpretive Summary:
Technical Abstract: There is little information on the responses of native grasslands to combined global change factors. This experiment examines how plant productivity in a northern mixed-grass prairie near Cheyenne, WY, USA responds to combined CO2 enrichment and warming. The Prairie Heating and CO2 Enrichment (PHACE) experiment consists of thirty 3-m diameter circular plots installed in native semi-arid grassland at the USDA-ARS High Plains Grasslands Research Station, west of Cheyenne, WY, USA. The focus of this presentation is on 20 plots assigned to a factorial combination of two CO2 (present ambient [380 ppm], and elevated [600 ppm] CO2, c and C respectively), and two temperature regimes (present ambient, and elevated temperature [1.5/3.0 C warmer day/night], t and T, respectively), with five replications. Measurements of aboveground plant biomass (AGB) were determined in late July each year, the time of peak aboveground biomass. Results are presented for two years only, the pre-treatment year of 2005, and in 2007 when both CO2 enrichment and warming had been initiated. Both total and functional group AGB differed in some of the treatment circles prior to initiation of the CO2 and warming treatments, so statistical tests for treatment effects were performed by evaluating differences in AGB before (2005) and after (2007) treatments had begun. Precipitation was higher in 2005 ( mm) compared to 2007 ( mm). As a result, total AGB declined from 2005 to 2007, but declined 13.5 g m-2 more under present ambient [CO2], indicating elevated CO2 enhanced AGB. Warming had no effect on total AGB. The C3 grasses, which dominate this grassland, displayed similar AGB responses to CO2 and warming as total AGB (Figure 2). However, AGB of C4 grasses was enhanced in 2007 by both CO2 and warming. Our preliminary results confirm earlier reports that CO2 enrichment enhances plant production in semi-arid grasslands. Further, they suggest combined rising CO2 and temperature may favor productivity of warm-season, C4 grasses.