What was done
The authors studied various water-related parameters in three types of Mediterranean shrubs that had been growing for several generations within the vicinity of a natural CO2-emitting spring near Pisa, Italy, where atmospheric CO2 concentrations ranged from 350 to 700 ppm.

What was learned
Elevated CO2 altered the elastic cell-wall properties of all three shrubs in such a way as to endow the shrubs with greater capacities for water uptake from the soil than are currently possessed by control plants growing in ambient air.  In addition, the CO2-enriched plants displayed greater relative water contents than did ambiently-grown plants as leaf water potentials declined with available soil moisture.

What it means
As the air's CO2 content continues to climb, these Mediterranean shrubs will likely develop increasingly greater drought tolerances than those of similar shrubs growing at today's atmospheric CO2 concentration.  Consequently, they should be able to expand their ranges into areas that have historically been too dry for them to survive and successfully reproduce.