Water relations and mineral nutrition of closely related woody plant species on desert dunes and interdunes

Abstract

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.

Rapid recovery of photosynthesis and water relations following soil drying and re-watering is related to the adaptation of desert shrub Ephedra alata subsp. alenda (Ephedraceae) to arid environments

“…Compared with other leafless perennial species of the shrubby genus Calligonum found in the same environment (Grand Erg Oriental), Dhief et al (2009) reported that all species reached less negative « w values (≈−2.5 MPa) during the hot and dry summer, with extremes in July. The findings are comparable with those of Grigg et al (2008) on desert plants inhabiting sandy soils where Acacia species typically displayed more negative leaf « w values, approaching −3.0 MPa for Acacia jensenii in the dry season. Plants on the dunes would display more favourable water relations (higher g s and less negative leaf « w ) than closely related plant species in the interdunes because of the greater soil depth and associated water storage capacity within the sandy dune ridges (Grigg et al, 2008;Dhief et al, 2009).…”

“…The findings are comparable with those of Grigg et al (2008) on desert plants inhabiting sandy soils where Acacia species typically displayed more negative leaf « w values, approaching −3.0 MPa for Acacia jensenii in the dry season. Plants on the dunes would display more favourable water relations (higher g s and less negative leaf « w ) than closely related plant species in the interdunes because of the greater soil depth and associated water storage capacity within the sandy dune ridges (Grigg et al, 2008;Dhief et al, 2009). In the case of Ephedra, the 10-12 m high dunes provide a large volume with a reasonable matric potential to store rainfall.…”

“…Desert plants regulate their water status and adapt to their heterogeneously stressful environment through a multiplicity of ecophysiological features by following two major strategies in relation to drought, based upon variation in phenology (deciduousness) and ability to tolerate water deficit (persistence) (Ackerly, 2004). Soil depth and texture are considered to be the most important edaphic properties that influence plant moisture regimes in arid environments with episodic rainfall (Grigg et al, 2008;Dhief et al, 2009).…”

Leaf manganese accumulation and phosphorus-acquisition efficiency

“…Leaf [Mn] in eucalypts are so high (800 mg Mn g À1 DW in green leaf-fall and up to 2800 mg Mn g À1 DW in leaves of glasshouse-grown seedlings) that they are within the toxic range for most plants [14]. The mechanism for Mn accumulation is unknown for these and other eucalypts [56], but we do know that Eucalyptus gummifera can access poorly soluble forms of inorganic P (aluminium phosphate and iron phosphate) [57], presumably through the releases of carboxylates.…”

Low-phosphorus conditions affect the nitrogen nutrition and associated carbon costs of two legume tree species from a Mediterranean-type ecosystem

“…Virgilia is one of tree legume genera that are endemic to these CFR (fynbos) acidic soils. Mediterranean acidic soils usually have different concentrations of elements, coupled with related nutrient deficiencies, associated with nitrogen (N) and phosphorus (P) deficiencies (Bordeleau and Prevost 1994;von Uexkull and Mutert 1998;Grigg et al 2008). Soil acidity is a significant problem facing legume and agricultural production in many areas of the world, including southern Africa (Graham 1992;Bordeleau and Prevost 1994;Marschner 1995;Correa and Barneix 1997).…”