Phenotypic plasticity and water availability: responses of alpine herb species along an elevation gradient

Background Alpine regions are particularly vulnerable to the effects of climate change. The Australian Alps are potentially more so than other mountain regions, as they cover a very small geographic area (<0.05% of mainland Australia), with a low maximum elevation (2228 m). Therefore, response to climate change will be primarily determined by the ability of species to survive in-situ through local adaptation or phenotypic plasticity. Existing climate change models project not only warming but increasingly variable precipitation and snow cover across the Australian Alps. Thus, plasticity in water use traits may become increasingly important for the establishment and persistence of Australian alpine plants. Given that plants from lower elevations inhabit a more heterogeneous environment with more frequent frosts, greater temperature extremes, and higher evapotranspiration, we predict plasticity – and particularly adaptive plasticity – may be more common at low relative to high elevation. To test these predictions we investigated the extent of plasticity and the adaptive value thereof in water use traits in three herbaceous Australian alpine plant species. Seeds were collected from low and high elevation alpine sites and grown at ample and limiting water availability under common-garden conditions. For morphological and physiological traits, we compared both their means and phenotypic plasticity across treatments and elevations. Results Responses of morphological and physiological traits to water availability were in accord with many previous studies of water response. Although previous work in the same environment demonstrated greater plasticity in response to temperature for low elevation populations, plasticity in response to water availability in our study showed markedly little variation as a function of elevation. Rather, patterns of plasticity were highly variable among species and among traits within species, with few instances of adaptive plastic responses. Conclusion We discuss the difficulties in observing adaptive plasticity and the importance of microhabitat variation in shaping the persistence of these Australian alpine species.S.R.G was supported by an Australian Government Research Training Program (RTP) Scholarship. J.A.R-V was supported by a González Esparcia postdoctoral scholarship from the Technical University of Madrid. We also acknowledge an Australian Research Council fellowship to A.B.N, FT100100464