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Vegetation on dunes and interdunes in hot, subtropical deserts is profoundly influenced by the temporal and spatial variation in availability of water and nutrients in the landscape. We hypothesised that water is more available to plants on the dunes but that nutrients are in greater concentrations on the interdunes in the Great Sandy Desert, Western Australia. During the course of 2 years, we examined water relations and photosynthesis of six dominant woody species throughout each season, in addition to foliar δ13C, δ15N and nutrient composition. In general, stomatal conductance (gs) was greater and leaf water potential (ΨL) less negative for dune species than for closely related species on the interdunes. The largest tree species in the landscape, Corymbia chippendalei ((D.J.Carr & S.G.M.Carr) K.D.Hill & L.A.S.Johnson), occurred only on the dunes, and maintained moderate gs values year round, ranging between 240 mmol H2O m–2 s–1 in the wet season and 160 mmol H2O m–2 s–1 in the middle of the dry season. It also displayed a relatively stable ΨL, between –0.3 and –0.5 MPa at predawn, and between –1.3 and –1.6 MPa at midday throughout the year, unlike the closely related species on the interdunes, Eucalyptus victrix (L.A.S.Johnson & K.D.Hill), which always displayed significantly lower ΨL values (0.2–1.1 MPa more negative). The two Grevillea species displayed ΨL values within a similar range as for C. chippendalei, while the Acacia species exhibited consistently more negative values, especially late in the dry season. Considerable reductions in gs occurred at this time for all species, except C. chippendalei. Rates of photosynthesis (A) followed the trends in gs, yet δ13C values varied little between related species in the dune and interdune habitats. Mineral nutrient concentrations in soil and foliage tended to be greater in the interdunes. Average N : P ratio in foliage was 28 : 1, indicating P was more limiting than N. Soil depth and texture, in conjunction with their effects on water availability and root growth, were considered to be the most influential factors affecting plant distribution in the Great Sandy Desert. It is concluded that dunes hold relatively more water than adjacent interdunes, sustaining more favourable water status in deep-rooted species from this habitat, further into the dry season. Conversely, species on the interdunes must be more desiccation tolerant and develop root systems with greater ability to penetrate conglomerated lateritic gravel layers in order to access water where and when it is available.

Vegetation plays an essential role in mine-site rehabilitation as it serves to reduce erosion and extract moisture from the soil cover, thus minimising deep drainage to potentially hazardous materials below. Plant water-use patterns and root development are likely to be impacted where subsoils are physically and/or chemically inhospitable and close to the surface, particularly in arid and semi-arid environments where pulses of rainfall are infrequent and interspersed with long dry periods. The aim of this investigation was to determine how plant water relations of the woody shrub species Acacia ancistrocarpa (Maiden and Blakely) were affected by a summer wetting pulse on a degraded mine-rehabilitation site and a pristine natural site in the Great Sandy Desert of north-western Australia. At both the natural and rehabilitation sites, 20 m 3 of water was applied to emulate an 80-mm rainfall event comparable with cyclones that occur during the summer wet season. We found that plants responded with significant increases in stomatal conductance, leaf water potential and sap-flow in lateral roots within three days of irrigation at the natural site and two days at the rehabilitation site. At the rehabilitation site this response occurred despite the fact that sinker roots were stunted by impeding physical properties of the mine-waste material. Sap-flow velocity, using the heat ratio method, in lateral and primary sinker roots was close to zero at night and positive during the day for trees at both sites during the dry period before the irrigation. These data indicate hydraulic redistribution was not occurring between the primary sinker and lateral roots at night, and water was transported along the laterals towards the crown, despite the fact they were in dry soil. Excavations revealed that lateral roots extended up to 6 m and displayed secondary sinker roots accessing water from deeper soil layers, even from mine-waste material. These morphological traits likely improved the water relations and survival of A. ancistrocarpa at the rehabilitation site. Considering these traits and the rapid pulse responsiveness of this species, we recommend A. ancistrocarpa for future rehabilitation projects at this and other mine-sites in the region.

Desert dunes and interdunes provide habitat heterogeneity and profoundly influence the spatial and temporal distribution of water and nutrients throughout the landscape. These underlying physical processes shape the plant species composition and their ecophysiology. Spinifex grasses dominate the vegetation throughout much of Australia and are categorised into two groups; ‘soft’ species occur mostly in northern, subtropical to semiarid regions, whereas ‘hard’ species occur mostly throughout the dry centre and southern interior. This study examined the water and nutrient relations and leaf anatomy of dominant ‘soft’ and ‘hard’ spinifex in the Great Sandy Desert, where their distributions overlap. The ‘soft’ species, Triodia schinzii (Henrard) Lazarides, occurs only on sand dunes, whereas the ‘hard’ species, T. basedowii E.Pritz., is restricted to the flat interdunes. We proposed two hypotheses: 1) that the dune species, T. schinzii would display more favourable water status and 2) the interdune species, T. basedowii would display higher leaf nutrient concentrations. Triodia schinzii displayed significantly less negative leaf water potentials at predawn and at midday (–0.4 and –2.0 MPa, respectively) than T. basedowii (–0.9 and –3.0 MPa, respectively) throughout the middle of the dry season. Photosynthesis rates were also significantly higher in T. schinzii than T. basedowii in the wet season (140 v. 84 nmol g–1 s–1), but there were no significant differences between species in leaf conductance. Leaf δ13C composition confirmed anatomical observations that both species were C4 and supported the finding that T. schinzii displayed significantly greater photosynthetic water-use efficiency during the wet season than T. basedowii. In general, foliar nutrient concentrations were not significantly different between species; however, both species exhibited especially low leaf P and to a lesser extent N. We conclude that water is more readily available in the dune than the interdune as a result of greater soil depth and associated water storage capacity. These properties are considered the main factors influencing plant species distribution. Given the climatic and geographic distribution of these two Triodia species, it is suggested that sand dunes provide a mesic corridor for T. schinzii to extend its range from higher rainfall areas into the arid interior.