Cheatgrass is favored by warming but not CO sub(2) enrichment in a semi-arid grassland

• Published in: Global change biology Vol. 22; no. 9; pp. 3026 - 3038
• Main Authors: Blumenthal, Dana M, Kray, Julie A, Ortmans, William, Ziska, Lewis H, Pendall, Elise
• Format: Journal Article
• Language: English
• Published: 01.09.2016
• Subjects: Bromus tectorum; North America
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.13278

Elevated CO sub(2) and warming may alter terrestrial ecosystems by promoting invasive plants with strong community and ecosystem impacts. Invasive plant responses to elevated CO sub(2) 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 CO sub(2) enrichment (to 600 ppmv) and infrared warming (+1.5 degree C day/3 degree 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 CO sub(2) 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 CO sub(2) decreases N availability, CO sub(2) may have limited effects on B. tectorum and other nitrophilic invasive species.