What was done
The authors conducted a FACE experiment in the southern California chaparral by exposing Adenostoma fassciculatum shrubs to differential atmospheric CO2 concentrations (360 and 550 ppm) for six weeks to study the effects of elevated CO2 on gas-exchange in this species.

What was learned
After six months of fumigation, photosynthetic acclimation occurred.  In addition, elevated CO2 must have reduced stomatal conductance, and consequently transpirational water loss, because CO2-enriched shrubs exhibited leaf water potential values that were more positive (less stressful) than control plants.  These data reveal that this species responds to atmospheric CO2 enrichment, and suggest that biomass data need to be obtained to determine how these altered physiological characteristics will eventually impact the growth of the plant.

What it means
As the CO2 content of the air increases, it is likely that this shrub will respond by reducing its stomatal conductance and transpiration rates, thereby enhancing its internal water status, which should enable this woody perennial to better withstand periods of drought that commonly occur in its southern California habitat.  In addition, photosynthetic down regulation should allow this shrub to better optimize limiting resources within its tissues and among different physiological processes.