However,
there are situations where elevated CO2 had no positive effect on
the physiological parameters and growth of water stressed plants
(Vaz et al., 2012; Perry et al., 2013). The net effects of CO2 on
growth and dry mass production under water stress depend on
the balance between direct effects of CO2 on both photosynthesis
and stomatal aperture (Manderscheid and Weigel, 2007). In some
cases, the effect of increased CO2 concentration on this balance is
not sufficient to allow some species to improve their growth under
water deficit (Perry et al., 2013), partially explaining the different
responses between species.