Rapid evolution of a desert plant invader (Bromus rubens) in response to elevated atmospheric CO2

The potential for plants to evolve rapidly in response to global change has not been adequately addressed. In fact, the success of biological invaders like red brome (Bromus rubens) may be due, in part, to their ability to evolve rapidly in response to global change. Elevated atmospheric CO₂ is one aspect of global change that has been studied in long-term experiments like the Nevada Desert Free Atmospheric Carbon Dioxide Enrichment Facility (NDFF). We examined whether red brome populations at the NDFF evolved in response to elevated CO₂ treatments applied from 1997-2003. Using a series of common garden and growth chamber experiments, we detected significant genetic differences in ecophysiological traits between populations of B. rubens exposed to ambient and elevated levels of atmospheric CO₂. Stomatal conductance and water-use efficiency were significantly lower in populations exposed to elevated atmospheric CO₂. These responses are what one might expect for plants under elevated atmospheric CO₂ and probably reflect a down-regulation of photosynthetic assimilation. In addition, plasticity for stomatal conductance was significantly lower in populations exposed to elevated atmospheric CO₂. It is remarkable (and a bit disconcerting) that there have been evolutionary responses in complex physiological traits within these weed populations in less than seven years.