What was done
The authors grew five-year-old seedlings of two olive cultivars in pots placed within FACE arrays maintained at atmospheric CO2 concentrations of 360 and 560 ppm for seven to eight months in a study designed to evaluate the effects of elevated CO2 on gas exchange in this economically important tree species.

What was learned
Elevated CO2 enhanced rates of net photosynthesis by an average of 38% in both cultivars.  In addition, it reduced stomatal conductances by an average of 30%.  Consequently, instantaneous water-use efficiency increased by approximately 80% in both cultivars.  Moreover, analyses of rubisco kinetics indicated elevated CO2 did not induce photosynthetic acclimation in either cultivar.

What it means
As the air's CO2 content continues to rise, olive trees growing in semi-arid Mediterranean-type climates will likely exhibit significant increases in water-use efficiency, which should allow them to better cope with recurring drought conditions that are common in such areas.