title: Cheatgrass is favored by warming but not CO2 enrichment in a semi-arid grassland.
abstract: Elevated CO2 and warming may alter terrestrial ecosystems by promoting invasive plants with strong community and ecosystem impacts. Invasive plant responses to elevated CO2 and warming are difficult to predict, however, because of the many mechanisms involved, including modification of phenology, physiology, and cycling of nitrogen and water. Understanding the relative and interactive importance of these processes requires multifactor experiments under realistic field conditions. Here, we test how free-air CO2 enrichment (to 600 ppmv) and infrared warming (+1.5 °C day/3 °C night) influence a functionally and phenologically distinct invasive plant in semi-arid mixed-grass prairie. Bromus tectorum (cheatgrass), a fast-growing Eurasian winter annual grass, increases fire frequency and reduces biological diversity across millions of hectares in western North America. Across 2 years, we found that warming more than tripled B. tectorum biomass and seed production, due to a combination of increased recruitment and increased growth. These results were observed with and without competition from native species, under wet and dry conditions (corresponding with tenfold differences in B. tectorum biomass), and despite the fact that warming reduced soil water. In contrast, elevated CO2 had little effect on B. tectorum invasion or soil water, while reducing soil and plant nitrogen (N). We conclude that (1) warming may expand B. tectorum's phenological niche, allowing it to more successfully colonize the extensive, invasion-resistant northern mixed-grass prairie, and (2) in ecosystems where elevated CO2 decreases N availability, CO2 may have limited effects on B. tectorum and other nitrophilic invasive species.
authors.affiliation: Rangeland Resources Research Unit, USDA Agricultural Research Service, Fort Collins, CO, USA.
authors.forename: Dana M
authors.initials: DM
authors.lastname: Blumenthal
authors.affiliation: Rangeland Resources Research Unit, USDA Agricultural Research Service, Fort Collins, CO, USA.
authors.forename: Julie A
authors.initials: JA
authors.lastname: Kray
authors.affiliation: Biodiversity and Landscape Unit, Gembloux Agro-Bio Tech, University of Liege, Gembloux, Belgium.
authors.forename: William
authors.initials: W
authors.lastname: Ortmans
authors.affiliation: Crop Systems and Global Change Laboratory, USDA Agricultural Research Service, Beltsville, MD, USA.
authors.forename: Lewis H
authors.initials: LH
authors.lastname: Ziska
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Penrith, NSW, Australia.|Department of Botany & Program in Ecology, University of Wyoming, Laramie, WY, USA.
authors.forename: Elise
authors.initials: E
authors.lastname: Pendall
mesh_terms: D031724:Bromus; D017753:Ecosystem; D065948:Grassland; D009656:North America; D006109:Poaceae; D012987:Soil
chemical_list: D012987:Soil
keywords: Great Plains grasslands; climate change; global warming; growing season length; nitrogen limitation; plant invasion; plant phenology; rangeland ecosystems