Response of 25-day old Eucalyptus globulus to elevated CO2

Increasing [CO2] may influence commercial crop and timber yield. While
selection of genotypes sensitive to elevated [CO2] (e[CO2]) appears
possible in agricultural crops, there is limited evidence for
genotype-by-CO2 (G×CO2) interactions in commercial tree species. We
examined [CO2] responsiveness in 124 open-pollinated Eucalyptus globulus
subspecies globulus (E. globulus) families with the aim of assessing
whether G×CO2 interactions are detectable in seedlings for early-age
screening. Plants were grown in ambient (a[CO2]; ~405 μmol mol-1) and
e[CO2] (640 μmol mol-1) and harvested 25 days after germination. Total,
shoot and root dry weights were determined for each plant. Carbon isotopic
discrimination against 13C (Δ13C) was determined at the family level. We
observed highly significant (p<0.0001) increases in mean total,
shoot, and root dry weights. Mixed-model equations were used to estimate
the main and interaction effects of the G×CO2 for each mass trait. The
main effects from the mixed model output ([CO2] and individual-tree
effects) were significant for all traits. However, [CO2]-by-individual
tree interactions were non-significant for all traits, indicating little
G×CO2 interaction. A secondary aim was to examine the correlation between
greenhouse and mature-age growth from breeding trials that use common
families conducted under ambient [CO2]. These correlations were
non-significant, suggesting early growth is not necessarily indicative of
later-age responses.  Our results suggest that while early growth
of E. globulus is enhanced under e[CO2], genotypes respond relatively
uniformly to e[CO2] and little opportunity exists for seedling-based
selection at the population level based upon the response of plants during
the first weeks of growth.