Evidence for adaptation and acclimation in a widespread eucalypt of semi-arid Australia

As climates change, restoration programmes need to maximize the capacity of regenerating ecosystems to adapt to new environments, particularly when planting long-lived trees. By using a combined phenotypic and genomic approach, we assessed evidence of adaptation capacity in Eucalyptus loxophleba ssp. lissophloia, a mallee eucalypt important for restoration and oil production in Western Australia. Assessment of leaf traits in nine wild populations across a rainfall gradient showed that two traits were correlated with long-term moisture availability. Populations in more arid environments had lower specific leaf area and lower stomatal conductance, consistent with a stable plastic or adaptive response. Other leaf size and shape traits were correlated with short-term climate variables, suggesting a dynamic plastic response. Genome-wide scans with 4851 DArTseq markers and outlier analysis detected 50 markers showing signals of disruptive selection, consistent with local adaptation. Sixteen markers showed allele frequencies correlated with aridity; three were also associated with differences in stomatal conductance. Multivariate analysis and marker-environment associations signalled secondary directions of adaptation associated with maximum temperatures and soil phosphorus. We suggest that adaptation and acclimation are both likely determinants of functional phenotype in E. loxophleba, and argue that aridity is a critical driver of adaptation in this widespread species.