PARENT SESSION
Oral Session # 37: Invasive Species III: Grasses and Shrubs.
Presiding: C Lortie
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Meeting Room 205.

Carbon dioxide enrichment reduces the energetic cost of biomass construction in an invasive desert grass.

Nagel, Jennifer^*,1, Huxman, Travis², Griffin, Kevin³, Smith, Stanley⁴, ¹ Texas Tech University, Lubbock, TX² University of Arizona, Tucson, AZ³ Columbia University, Palisades, NY⁴ University of Nevada, Las Vegas, NV

ABSTRACT- A central issue in plant ecology is how plant communities will be impacted by human-induced environmental changes. These community-level changes will be influenced by the differential responses of constituent species to changing resources. Evaluating the effects of projected changes in resource availability on co-occurring nonindigenous and native plant species in invaded ecosystems could provide insight useful in developing reliable predictions of how these plant communities could change in the future. While deserts presently are among the least invaded ecosystems, they have been predicted to be one of the most responsive ecosystems to global change. To examine how increasing atmospheric CO₂ partial pressure could influence invasion dynamics in an intact Mojave Desert ecosystem, we compared the responses of energetic properties and growth of invasive and native grass species to atmospheric CO₂ enrichment at the Nevada Desert Free-Air CO₂ Enrichment Facility. Combined with its modest positive 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 and bigger and produced more seeds with atmospheric CO₂ enrichment than the native grass species. Because plant growth involves both the assimilation and expenditure of energy, it has been suggested that the most successful plant species in a given environment could be those that maximize their energetic gains while minimizing their energetic costs. As a physiological mechanism of invasive species success driven by CO₂ enrichment, such reductions in the energetic cost of biomass construction combined with increased photosynthetic activity could trigger a shift in the species composition of this Mojave Desert ecosystem, and potentially that of other invaded ecosystems, toward increased invasive species dominance.

Key words: photosynthesis, construction cost, energetics, Bromus madritensis spp. rubens