Water stress vulnerability of four Banksia species in contrasting ecohydrological habitats on the Gnangara Mound, Western Australia.

This study investigated the interspecific differences in vulnerability to xylem embolism of four phreatophytes - two facultative phreatophytes (Banksia attenuata and B. menziesii) and two obligate phreatophytes (B. ilicifolia and B. littoralis). Species differences at the same position along an ecohydrological gradient on the Gnangara Groundwater Mound, Western Australia were determined in addition to intraspecific differences to water stress between populations in contrasting ecohydrological habitats. Stem- and leaf-specific hydraulic conductivity, as well as Huber values (ratio of stem to leaf area), were also determined to support these findings. We found that where water is readily accessible, there were no interspecific differences in vulnerability to water stress. In contrast both facultative phreatophyte species were more resistant to xylem embolism at the more xeric dune crest site than at the wetter bottom slope site. B. ilicifolia did not differ in vulnerability to embolism, supporting its classification as an obligate phreatophyte. Other measured hydraulic traits (K(S), K(L) and Huber value) showed no adaptive responses, although there was a tendency for plants at the wetter site to have higher K(S) and K(L). This study highlights the influence site hydrological attributes can have on plant hydraulic architecture across species and environmental gradients.