To more fully understand how a species’ lineage could influence its functional traits, we need more information on how closely related species differ along resource gradients. These insights would be even more powerful in species that have only recently radiated because the observed changes would likely be the result of selection on specific traits that allow for survival, not drift. To address these gaps, we grew 10 closely related species in four common gardens along an aridity gradient in Victoria, Australia to ask about variation in a wide range of traits. This design also allowed us to examine the extent of intraspecific plasticity along the gradient.
The 10 species we examined consisted of five species each of two of the subgenera of Eucalyptus. Within each subgenus, the five species’ ranges were distributed along the same aridity gradient where the common gardens were located. We quantified the extent to which species were adapted to arid environments by comparing the ratio of precipitation to pan evaporation (P/Ep) of their home ranges. Our species’ average P/Ep ranged from ~0.2 to ~0.9. to examine how traits vary within and among lineages, we measured specific leaf area (SLA), maximum photosynthesis (Amax), maximum stem hydraulic conductivity (Ks), and wood density.
Results/Conclusions
Within each garden, as moisture availability in a species’ native range increased, SLA and Amax did too. Comparing intraspecific plasticity across common gardens, SLA and Amax also increased in plants at the moister sites. Wood density was lower in species adapted to drier environments, but species from the two subgenera differed in their changes in wood density. Species in the subgenus Symphyomyrtus all increased wood density at drier sites at the same rate, regardless of native P/Ep. Subgenus Eucalyptus species from drier habitats increased wood density to a greater extent in drier gardens than species adapted to moister habitats. Species adapted to drier sites exhibited far less variation in Ks than species from wetter sites. Specifically, dry-adapted species grown under wetter conditions did not increase their hydraulic conductivity to the extent that moist-adapted species did. In contrast, species adapted to wetter sites greatly reduced their Ks when grown at the drier sites. These results provide insight into how recently evolved lineages often, but not always, exhibit similar responses to variation in moisture supply.