Early-growth results within a Eucalyptus globulus breeding population suggest limited scope for selection focused on CO2 responsiveness

Abstract

Increasing [CO 2 ] may influence commercial crop and timber yield. While selection of genotypes sensitive to elevated [CO 2 ] (e[CO 2 ]) appears possible in agricultural crops, there is limited evidence for genotype-by-CO 2 (G × CO 2 ) interactions in commercial tree species. We examined [CO 2 ] responsiveness in 124 open-pollinated Eucalyptus globulus ssp. globulus ( E. globulus ) families with the aim of assessing whether G × CO 2 interactions are detectable in seedlings for early-age screening. Plants were grown in ambient (a[CO 2 ]; ~ 405 μmol mol −1 ) and e[CO 2 ] (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 13 C (Δ 13 C) 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 × CO 2 for each mass trait. The main effects from the mixed-model output ([CO 2 ] and individual-tree effects) were significant for all traits. However, [CO 2 ]-by-individual tree interactions were non-significant for all traits, indicating little G × CO 2 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 [CO 2 ]. 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[CO 2 ], genotypes respond relatively uniformly to e[CO 2 ] and little opportunity exists for seedling-based selection at the population level based upon the response of plants during the first weeks of growth.

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