Alternatively, experimental results such as those in Table 1 could
be used to identify candidate traits that confer superior e[CO2]
response. A subset of the most promising traits could be tested
in field scale FACE facilities, and then become selection targets for
breeding efforts (Ainsworth et al., 2008a). Time spans to release
new cultivars are sometimes 10–20 years, even if target traits
are known (Semenov and Halford, 2009). It is therefore urgent
to better understand the fundamental physiology of intra-specific
variability in e[CO2] response and identify target traits. Perhaps
most importantly, the environmental circumstances where these
traits are of practical importance as selection targets must be
assessed.