Contemporary evolution of an invasive grass in response to elevated atmospheric CO(2) at a Mojave Desert FACE site

Elevated atmospheric CO(2) has been shown to rapidly alter plant physiology and ecosystem productivity, but contemporary evolutionary responses to increased CO(2) have yet to be demonstrated in the field. At a Mojave Desert FACE (free-air CO(2) enrichment) facility, we tested whether an annual grass weed (Bromus madritensis ssp. rubens) has evolved in response to elevated atmospheric CO(2). Within 7 years, field populations exposed to elevated CO(2) evolved lower rates of leaf stomatal conductance; a physiological adaptation known to conserve water in other desert or water-limited ecosystems. Evolution of lower conductance was accompanied by reduced plasticity in upregulating conductance when CO(2) was more limiting; this reduction in conductance plasticity suggests that genetic assimilation may be ongoing. Reproductive fitness costs associated with this reduction in phenotypic plasticity were demonstrated under ambient levels of CO(2). Our findings suggest that contemporary evolution may facilitate this invasive species' spread in this desert ecosystem.