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Interactive Effects of Elevated CO2 and Drought on Cherry Seedling Growth and Water-Use Efficiency
Centritto, M., Lee, H.S.J. and Jarvis, P.G.  1999.  Interactive effects of elevated [CO2] and drought on cherry (Prunus avium) seedlings.  I.  Growth, whole-plant water use efficiency and water loss.  New Phytologist 141: 129-140.

What was done
Cherry seedlings were grown from germination for two full years in open-top chambers with ambient (350 ppm) or twice-ambient (700 ppm) levels of atmospheric CO2.  During the first growing season, half of the seedlings were exposed to a gradually-developing water stress treatment by withholding irrigation for a 6-week period.  These same seedlings were subsequently exposed to a rapid water stress treatment during the height of the next year's growing season.  These manipulations allowed the authors to study the interactive effects of elevated CO2 and water stress on cherry seedling growth and water use.

What was learned
By the end of the second growing season, elevated CO2 had significantly increased basal trunk area by 22 and 69% for well-watered and water-stressed seedlings, respectively, in comparison with controls grown at ambient CO2.  In addition, total seedling dry mass was significantly higher with atmospheric CO2 enrichment throughout the entire study, regardless of drought conditions.  Although the total amount of seedling water loss did not vary much with CO2 treatment, total plant water-use efficiency was significantly enhanced due to the CO2-induced stimulation of seedling dry mass.  During well-watered and water-stressed conditions, for example, elevated CO2 increased seedling water-use efficiency by 47 and 51%, respectively.

What it means
As the CO2 content of the air increases, cherry seedlings will likely respond by increasing their overall size and biomass, even during times of periodic and repeated water stress.  In addition, if seedling water loss remains constant as the level of atmospheric CO2 rises, their water-use efficiency will also rise, possibly allowing them to be grown in drier regions than where they currently are found.

Reviewed 1 May 1999