Investigation of the niche partitioning of selected Ranunculaceae species in Kosciuszko National Park along a soil moisture gradient, by comparison of hydraulic characteristics

Environmental gradients that function as niche partitioning axes underpin plant biodiversity. Alpine zones are recognised biodiversity centres particularly threatened by a changing climate, which may alter such gradients. The soil water content (SWC) of coexisting Ranunculaceae in alpine and subalpine zones of Kosciuszko National Park, Australia (Caltha introloba, Ranunculus gunnianus, Ranunculus muelleri and Ranunculus graniticola) was investigated as a potential ecological niche division. We hypothesised that study species will be found in soils of distinct SWC, and hydraulic leaf characteristics will vary between species with respect to this gradient. As hypothesised, species were distributed along a statistically distinct soil water gradient (P<0.001), with C. introloba found in soils of highest SWC. Whilst R. gunnianus was found in soils of higher mean SWC than the other Ranunculus species studied, the significance of this data could not be determined. In accordance with previous studies, the species of highest SWC, C. introloba, was found to have the leaf surface with highest stomatal density (P<0.0001); highest adaxial stomatal density (P<0.0001); largest xylem diameter; and lowest xylem density within a petiole section. Notably, a distinct trend of higher SLA for species of lower SWC was determined (P<0.0001) in contradiction with the literature, which may have novel implications.