Competition between cheatgrass and bluebunch wheatgrass is altered by temperature, resource availability, and atmospheric CO2 concentration

Oecologia, Dec 2017

Global change drivers (elevated atmospheric CO2, rising surface temperatures, and changes in resource availability) have significant consequences for global plant communities. In the northern sagebrush steppe of North America, the invasive annual grass Bromus tectorum (cheatgrass) is expected to benefit from projected warmer and drier conditions, as well as increased CO2 and nutrient availability. In growth chambers, we addressed this expectation using two replacement series experiments designed to test competition between B. tectorum and the native perennial bunchgrass Pseudoroegneria spicata. In the first experiment, we tested the effects of elevated temperature, decreased water and increased nutrient availability, on competition between the two species. In the second, we tested the effects of elevated atmospheric CO2 and decreased water availability on the competitive dynamic. In both experiments, under all conditions, P. spicata suppressed B. tectorum, though, in experiment one, warmer and drier conditions and elevated nutrient availability increased B. tectorum’s competitiveness. In experiment two, when grown in monoculture, both species responded positively to elevated CO2. However, when grown in competition, elevated CO2 increased P. spicata’s suppressive effect, and the combination of dry soil conditions and elevated CO2 enhanced this effect. Our findings demonstrate that B. tectorum competitiveness with P. spicata responds differently to global change drivers; thus, future conditions are unlikely to facilitate B. tectorum invasion into established P. spicata communities of the northern sagebrush steppe. However, disturbance (e.g., fire) to these communities, and the associated increase in soil nutrients, elevates the risk of B. tectorum invasion.

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Competition between cheatgrass and bluebunch wheatgrass is altered by temperature, resource availability, and atmospheric CO2 concentration

Competition between cheatgrass and bluebunch wheatgrass is altered by temperature, resource availability, and atmospheric CO2 concentration Christian D. Larson 0 1 2 4 5 Erik A. Lehnhoff 0 1 2 4 5 Chance Noffsinger 0 1 2 4 5 Lisa J. Rew 0 1 2 4 5 0 Chance Noffsinger 1 Erik A. Lehnhoff 2 Communicated by Yu-Long Feng 3 Christian D. Larson 4 Entomology, Plant Pathology and Weed Science, New Mexico State University , Las Cruces, NM 88003 , USA 5 Weed and Invasive Plant Ecology and Management Group, Land Resources and Environmental Science Department, Montana State University , Bozeman, MT 59717 , USA Global change drivers (elevated atmospheric CO2, rising surface temperatures, and changes in resource availability) have significant consequences for global plant communities. In the northern sagebrush steppe of North America, the invasive annual grass Bromus tectorum (cheatgrass) is expected to benefit from projected warmer and drier conditions, as well as increased CO2 and nutrient availability. In growth chambers, we addressed this expectation using two replacement series experiments designed to test competition between B. tectorum and the native perennial bunchgrass Pseudoroegneria spicata. In the first experiment, we tested the effects of elevated temperature, decreased water and increased nutrient availability, on competition between the two species. In the second, we tested the effects of elevated atmospheric CO2 and decreased water availability on the competitive dynamic. In both experiments, under all conditions, P. spicata suppressed B. tectorum, though, in experiment one, warmer and drier conditions and elevated nutrient availability increased B. tectorum's competitiveness. In experiment two, when grown in monoculture, both species responded positively to elevated CO2. However, when grown in competition, elevated CO2 increased P. spicata's suppressive effect, and the combination of dry soil conditions and elevated CO2 enhanced this effect. Our findings demonstrate that B. tectorum competitiveness with P. spicata responds differently to global change drivers; thus, future conditions are unlikely to facilitate B. tectorum invasion into established P. spicata communities of the northern sagebrush steppe. However, disturbance (e.g., fire) to these communities, and the associated increase in soil nutrients, elevates the risk of B. tectorum invasion. Bromus tectorum; Climate change; Plant invasion; Pseudoroegneria spicata; Replacement series design Introduction Atmospheric CO2 concentrations have increased at an unprecedented rate since the beginning of the industrial era (IPCC 2013) . It is projected that the 2015–2016 atmospheric CO2 concentration growth rate will be highest on record and concentrations will surpass and remain above 400 ppm for the entire year (Betts et al. 2016) . The increase in atmospheric CO2 has altered many components of the Earth’s climate, including surface temperatures and precipitation patterns (IPCC 2013) . As plant growth is directly affected by temperature, precipitation (Woodward and Williams 1987) and atmospheric CO2 concentrations (Bazzaz 1990) , these changes have consequences for global plant communities (Shaver et al. 2000; Cramer et al. 2001; Walther et al. 2002; Parmesan and Yohe 2003; Chen et al. 2011) . Elevated atmospheric CO2 has long been used to stimulate plant production; however, plant attributes shape individual and group responses (Bazzaz 1990) . Elevated CO2 favors species with intrinsically higher growth rates because they have a higher maximum rate of photosynthesis and can more fully utilize the elevated resource level (Poorter and Navas 2003) . Non-native invasive plant species often have high relative growth rates; therefore, it is expected they will benefit from elevated CO2 (Dukes and Mooney 1999; Weltzin et al. 2003; Moore 2004; Sorte et al. 2013) . Consistent with this expectation, studies have found that non-native species demonstrate greater responses to elevated CO2 than native species (Ziska and George 2004), and elevated CO2 makes them more competitive with native species when grown together (Ziska and George 2004; Manea and Leishman 2011) . The presence, density, and identity of competitors influence non-native responses to elevated CO2 (Bazzaz et al. 1992; Wayne et al. 1999; Manea and Leishman 2011) . For example, the non-native species Centaurea solstitialis and Chenopodium album responded positively to elevated CO2 concentrations when grown in monoculture, but failed to respond significantly when grown in competitive settings (Taylor and Potvin 1997; Dukes 2002) . Resource levels also affect plant responses to elevated CO2 (Bazzaz 1990) . For example, by reducing stomatal density and conductance and increasing plant water use efficiency (Bazzaz 1990; Polley 1997; Morgan et al. 2004) , elevated CO2 can mitigate the negative effects of warming and drying on plant growth (Dermody et al. 2007) . Conversely, in (...truncated)


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Christian D. Larson, Erik A. Lehnhoff, Chance Noffsinger, Lisa J. Rew. Competition between cheatgrass and bluebunch wheatgrass is altered by temperature, resource availability, and atmospheric CO2 concentration, Oecologia, 2017, pp. 1-14, DOI: 10.1007/s00442-017-4046-6