What was done
The authors grew three Yucca species (brevifolia, schidigera, and whipplei) native to the Mojave Desert of the southwestern United States in pots placed within glasshouses receiving atmospheric CO2 concentrations of 360 and 700 ppm and day/night air temperatures of 40/24°C for seven months.  After that time, some of the plants were further subjected to a two-week day/night air temperature treatment of 20/5°C.  In addition, leaves from each Yucca species were removed and placed in an air freezer that reduced temperatures by 3°C per hour until a minimum value of -15°C was reached.  Thus, the authors investigated the effects of elevated CO2 exposure on low-temperature tolerance in these native desert species.

What was learned
Elevated CO2 enhanced low-temperature tolerance in all three Yucca species.  Specifically, elevated CO2 lowered the air temperature at which 50% low-temperature-induced cell mortality occurred by 1.6, 1.4 and 0.8°C in brevifolia, schidigera and whipplei, respectively.

What it means
As the air's CO2 content rises, the three Yucca species will likely become more adept at surviving periods of low-temperature exposure, which commonly occur in the Mojave Desert.  This CO2-induced low-temperature tolerance may also allow them to expand their ranges both northwards and upwards in elevation, where air temperatures are cooler than those they experience in their current ranges.  In the words of the authors, "increases in atmospheric air temperatures and concentrations of CO2 may allow seedlings to have a greater likelihood of surviving lower temperature and thereby establishing at higher elevations and latitudes in the future."