Genetic variation in Eucalyptus viminalis Labill. is limited for drought resistance traits but varies for lignotubers

Drought and fire stress acted independently in shaping the evolution of a widespread eucalypt species. The mixing of local and non-local seed sources (e.g., climate-adjusted provenancing) for revegetating damaged or degraded ecosystems assumes that the non-local genotypes growing in future climates will harbour genetic variation in traits important for maintaining fitness in drier/hotter environments, but this is rarely validated. To determine the extent to which genetic variation in traits associated with drought and recovery covaries with provenance homesite climate, we sampled multiple provenances of E. viminalis, collected from a precipitation gradient and grown in a common garden trial. We hypothesised that provenances from increasingly drier homesite environments will show greater resistance to failure of the hydraulic system and greater resource allocation to recovery traits, compared to provenances from wetter homesite environments. Contrary to expectation, we found no significant difference among provenances for drought traits and carbon resource allocation along the rainfall gradient. Mean xylem cavitation resistance (P50) and turgor loss point (TLP) in leaves did not differ significantly among provenances. However, we did find significant genetic-based variation in the recovery trait (relative lignotuber size) that was associated with the provenance homesite climate, and this trait was also independent of any of the drought traits studied. Relative lignotuber size was larger in individuals from increasingly arid provenances, consistent with selection favouring greater investment in recovery traits in environments where canopy loss is frequent, potentially due to disturbance such as fire or severe drought. These results suggest that recovery traits may represent a stronger or more consistent axis of selection than drought resistance traits in this species.