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To examine how global change could influence species invasions, we compared the responses of energetic processes and growth of invasive and native grass species to atmospheric CO2 enrichment in an intact Mojave Desert ecosystem. Combined with its modest influence on photosynthetic activity, elevated atmospheric CO2 was associated with a significant reduction in the energetic cost of aboveground biomass construction in invasive Bromus madritensis spp. rubens (red brome) without a concurrent cost reduction in native Vulpia octoflora (six-weeks fescue). Consequently, the invasive grass species grew faster, grew bigger, and produced more seeds with atmospheric CO2 enrichment than the native grass species. As a physiological mechanism of invasive species success driven by CO2 enrichment, such alterations in biomass construction costs combined with increased photosynthetic activity could trigger a shift in the species composition of this ecosystem, and potentially that of other invaded ecosystems, toward increased invasive species dominance.