Seeds of cherry (Prunus avium) were germinated and grown
for two growing seasons in ambient
(∼350 μmol mol−1) or elevated (ambient+∼350
μmol mol−1) CO2
mole fractions in six open-top chambers. The seedlings were
fertilized once a week, following Ingestad principles in order to supply
mineral nutrients at free-access rates. In
the first growing season gradual drought was imposed on rapidly growing
cherry seedlings by withholding water
for a 6-wk drying cycle. In the second growing season, the rapid onset
of drought was imposed at the height of
the growing season on the seedlings which had already experienced drought
in the first growing season. Elevated
[CO2] significantly increased total dry-mass production
in both water regimes, but did not ameliorate the growth
response to drought of the cherry seedlings subjected to two sequential
drying cycles. Water loss did not differ in
either well watered or droughted seedlings between elevated and ambient
[CO2]; consequently whole-plant water-
use efficiency (the ratio of total dry mass produced to total water consumption)
was significantly increased. Similar
patterns of carbon allocation between shoot and root were found in elevated
and ambient [CO2] when the seedlings
were the same size. Thus, elevated [CO2] did not improve
drought tolerance, but it accelerated ontogenetic
development irrespective of water status.