Climate has significant influence on the distribution of species and climate niche analysis is often used as a tool to predict species distribution in future climates. However, it is often not known if species with different climate envelopes also show differences in the expression of plant functional traits and if they respond differently to drought stress. We investigated this for five different subspecies of the widely distributed cosmopolitan shrub Dodonaea viscosa Jacq. The five subspecies occur in vastly different climates in Australia, ranging from tropics to temperate to desert ecosystems. Mean annual precipitation (MAP) for the subspecies ranged from 393 mm yr-1 to 1353 mm yr-1 and the mean aridity index (AI) ranged from 0.18 to 0.80. We hypothesised that subspecies from hotter and drier environments would be more anisohydric and have traits associated with drought tolerance than subspecies from more mesic habitats. We measured functional traits and drought response of the five sub-species in one-year old plants in a glasshouse experiment.
Results/Conclusions
Functional traits, such as leaf size, specific leaf area, turgor loss point, maximum stomatal conductance or maximum plant hydraulic conductance differed among the five subspecies. However, the differences were small for most traits and were not related to their climate of origin (MAP, MAP, AI). Drought response was also not related to climate of origin and was typical for drought avoiding plants. All subspecies closed stomata at very high water potentials (btw -1.0 to -1.3 MPa) and expressed large hydraulic safety margins. All subspecies adjusted their turgor loss points via osmotic adjustment and subspecies with inherently lower turgor loss points showed a greater osmotic adjustment. Hence, all subspecies showed typical isohydric behaviour and did not support our hypothesis that subspecies from more arid environments would be more drought tolerant. Our data indicate that climate niche is not always related to plant trait expression and to plant response to environmental stresses. Our data also indicate that differences in functional trait expression are not always related to differences in drought response. The exclusively isohydric drought avoidance behaviour seems to be a successful strategy for this widely distributed species in a vast array of different ecosystems.