'Acacia' s.s. comprises approximately 1020 species (i.e. just under one-third of all mimosoid legumes) and is almost entirely restricted to, although widespread, on the Australian continent. We investigated variation in the wood anatomy of 12 species from temperate New South Wales in a study concentrating on four recognised taxonomic sections ('Botrycephalae', 'Juliflorae', 'Phyllodineae' and 'Plurinerves'), to elucidate which characteristics are consistent within the sections, having removed climatic effect as much as possible. The sections had great utility in species identification, whereas none of the wood characters reflected the hypothesised phylogeny of the genus. The main consistent difference among species was in ray width (uniseriate versus 1-3 cells wide). All species had distinct growth rings. The vessels had alternate vestured pitting and simple perforation plates. Fibres were generally thick-walled, and many fibres had a gelatinous inner wall (tension wood fibres) and were inconsistently distributed. Axial parenchyma was mainly paratracheal, ranging from vasicentric to confluent and varied greatly in abundance. Prismatic crystals were usually present in chambered fibres and axial parenchyma strands, and also varied in abundance. The variation in these qualitative characters obscures taxonomic differences, but may allow inferences to be made about environmental adaptation.

This study examined the water relations of sclerophyllous evergreen vegetation (wallum) on coastal sand barriers in eastern Australia. Many wallum species may be groundwater dependent, although the extent of this dependency is largely unknown. Twenty-six perennial tree, shrub and herb species were investigated in three groundwater habitats (ridge, open depression, closed depression). Pre-dawn and midday shoot xylem water potentials (ᴪₓ) were measured monthly between late autumn 2010 and late summer 2011. Pressure-volume curve traits were determined in mid- to late spring 2009, including the osmotic potential at full (π100) and zero (π0) turgor, and bulk modulus of elasticity (ε). Carbon isotope ratios (δ¹³C) were also determined in mid- to late spring 2009, to measure water-use efficiency (WUE). The species displayed a range of physiological strategies in response to water relations, and these strategies overlapped among contrasting growth forms and habitats. Linear relationships between osmotic and elastic adjustment were significant. A strong correlation between δ¹³C and distribution along the hydrological gradient was not apparent. 'Banksia ericifolia' subsp. 'macrantha' (A.S.George) A.S.George, 'Eucalyptus racemosa' Cav. subsp. 'racemosa' and 'Eucalyptus robusta' Sm. displayed little seasonal variation in ᴪₓ and maintained a comparatively high pre-dawn ᴪₓ, and are therefore likely to be phreatophytic. Wetland vegetation in the lowest part of the landscape appeared to tolerate extreme fluctuations in water availability linked to a prevailing climatic pattern of variable and unreliable seasonal rainfall.

Hydroponic experiments were conducted to compare the effects of 'Pythium irregulare' and root pruning on wheat ('Triticum aestivum' cv. Janz) transpiration, water-use efficiency (WUE) and plant growth in the presence and absence of polyethylene glycol-induced drought (PEG). 'Pythium', PEG and root pruning reduced transpiration to a similar extent, but the mechanism that affects transpiration differed between the treatments. Reduced hydraulic conductivity of roots caused by disease in the 'Pythium' treatment and reduced size of the root system in the root pruning treatment were responsible for decreased transpiration while reduction of stomatal conductance was the main cause for reduced transpiration in the PEG treatment. 'Pythium' reduced shoot dry weight and increased root/shoot ratio but had no effect on whole-plant or instantaneous WUE. There was a small additive effect of 'Pythium' on whole-plant transpiration of plants exposed to PEG-induced drought, but there was no evidence of an interaction between 'Pythium' and PEG-induced drought on WUE or growth. This suggests that moderate root damage by pathogens is likely to have only a modest effect on the water relations of wheat plants.

The hypothesis that root rot caused by Pythium irregulare reduces the water use efficiency of wheat was tested in a system which simulated field conditions with late season water stress. Inoculation with Pythium significantly reduced transpiration during vegetative growth, so that plants entered post-anthesis drought with more available water. Although weekly transpiration rates were higher in inoculated plants than controls during the later stages of drought, infected plants were unable to make use of all of the extra water. There were no significant effects of inoculation on shoot biomass or grain yield, while total transpiration was reduced by 14%. Infected plants therefore had significantly higher integrated water use efficiency (grain yield relative to transpiration) than controls. Infected plants were significantly more stressed than controls during the drought, despite higher soil moisture, and showed reduced ability to use stomatal conductance to regulate leaf water potential. Pythium infection caused adverse changes to plant water use and water relations, but these did not translate into reductions in growth or yield. This, and the unexpected increase in water use efficiency, highlights the need to consider interactions with other environmental stresses when making assumptions about the effects of root diseases on crop productivity.

An investigation was made into the effects of long- and short-term water stress on the growth and water relations of species of Acacia belonging to four major sections of the subgenus Phyllodineae; the bipinnate-leaved Botrycephalae and the phyllodinous Juliflorae, Phyllodineae and Plurinerves. The germplasm was collected from sites within a narrow rainfall band [700–800 mm mean annual rainfall (m.a.r.)]. Shoot and root mass were significantly decreased in three of the four sections by water stress. The exception was the Juliflorae that showed a conservative growth strategy. A high root/shoot ratio is associated with tolerance to arid or semiarid environments, however, the highest root/shoot ratio was found for the temperate Botrycephalae. Measurements were made of the capacity for active and partial osmoregulation. All sections showed a biphasic response to drought stress for natural logarithm plots of relative water content (RWC) vs. osmotic potential in one or both experiments. This pattern of response has previously only been reported in a few plant species. Osmotic adjustment (OA) ranged from 1.6 MPa for the Botrycephalae to 3.4 MPa for Juliflorae at RWC of 60%. Active osmoregulation in the second phase was lower for the Botrycephalae and Phyllodineae than for the Juliflorae and Plurinerves. Although the germplasm was collected within a narrow and relatively high m.a.r. band, the sections with arid and semiarid relatives (Juliflorae and Plurinerves) still retained a higher degree of xeromorphic character and drought tolerance as determined by the growth responses and the higher capacity for OA.

Calcium oxalate (CaOx) crystals are a common natural feature of many plant families, including the Leguminosae. The functional role of crystals and the mechanisms that underlie their deposition remain largely unresolved. In several species, the seasonal deposition of crystals has been observed. To gain insight into the effects of rainfall on crystal formation, the morphology, distribution and accumulation of calcium oxalate crystals in phyllodes of the leguminous 'Acacia' sect. 'Juliflorae' (Benth.) C. Moore & Betche from four climate zones along an aridity gradient, was investigated. The shapes of crystals, which include rare Rosanoffian morphologies, were constant between species from different climate zones, implying that morphology was not affected by rainfall. The distribution and accumulation of CaOx crystals, however, did appear to be climate-related. Distribution was primarily governed by vein density, an architectural trait which has evolved in higher plants in response to increasing aridity. Furthermore, crystals were more abundant in acacias from low rainfall areas, and in phyllodes containing high concentrations of calcium, suggesting that both aridity and soil calcium levels play important roles in the precipitation of CaOx. As crystal formation appears to be calcium-induced, we propose that CaOx crystals in Acacia most likely function in bulk calcium regulation.

The present study examined the water relations of wallum dry sclerophyll woodland on the lower north coast of New South Wales (NSW). Wallum is the regionally distinct vegetation of Quaternary dunefields and beach ridge plains along the eastern coast of Australia. Wallum sand masses contain large aquifers, and previous studies have suggested that many of the plant species may be groundwater dependent. However, the extent of this dependency is largely unknown, despite an increasing reliance on the aquifers for groundwater extraction. Fifteen species from five growth-form categories and seven plant families were investigated. The pre-dawn and midday xylem water potential (Ψₓ) of all species was monitored over a 20-month period from December 2007 to July 2009. Pressure-volume curve traits were determined for each species in late autumn 2008, including the osmotic potential at full (π₁₀₀) and zero (π₀) turgor, and bulk modulus of elasticity (ε). Carbon isotope ratios (δ¹³C) were determined in mid-autumn 2008 to measure water use efficiency (WUE). Comparative differences in water relations could be loosely related to growth forms. A tree (Eucalyptus 'racemosa' subsp. 'racemosa') and most large shrubs had low midday Ψₓ, π₁₀₀ and π₀, and high ε and WUE; whereas the majority of small and medium shrubs had high midday Ψₓ, π₁₀₀ and π₀, and low ε and WUE.However, some species of similar growth form displayed contrasting behaviour in their water relations (e.g. the herbs 'Caustis recurvata' var. 'recurvata' and 'Hypolaena fastigiata'), and such differences require further investigation. The results suggest that 'E. racemosa' subsp. 'racemosa' is likely to be groundwater dependent, and large shrubs such as 'Banksia aemula' may also utilise groundwater. Both species are widespread in wallum, and therefore have the potential to play a key role in monitoring ecosystem health where aquifers are subject to groundwater extraction.

Background and Aims. This study investigates the structural diversity of the secondary xylem of 54 species of 'Acacia' from four taxonomic sections collected across five climate regions along a 1200 km E-W transect from sub-tropical [approx. 1400 mm mean annual precipitation (MAP)] to arid (approx. 240 mm MAP) in New South Wales, Australia. 'Acacia sensu stricto' (s.s.) is a critical group for understanding the effect of climate and phylogeny on the functional anatomy of wood. Methods. Wood samples were sectioned in transverse, tangential and radial planes for light microscopy and analysis. Key Results. The wood usually has thick-walled vessels and fibres, paratracheal parenchyma and uniseriate and biseriate rays, occasionally up to four cells wide. The greater abundance of gelatinous fibres in arid and semi-arid species may have ecological significance. Prismatic crystals in chambered fibres and axial parenchyma increased in abundance in semi-arid and arid species. Whereas vessel diameter showed only a small decrease from the sub-tropical to the arid region, there was a significant 2-fold increase in vessel frequency and a consequent 3-fold decrease in the vulnerability index. Conclusions. Although the underlying phylogeny determines the qualitative wood structure, climate has a significant influence on the functional wood anatomy of 'Acacia s.s.', which is an ideal genus to study the effect of these factors.

A pot experiment was conducted to investigate the effects of fungal root diseases ('Pythium' and 'Rhizoctonia') and drought at either tillering or anthesis on the water-use efficiency (WUE), water relations, yield components and percentage of root lesion of two Australian bread-wheat cultivars (Mulgara and Janz). There were no significant differences between two pathogens. WUE did not differ between well-watered plants and those droughted at tillering but it was significantly reduced by drought at anthesis. Mulgara had slightly higher WUE than Janz. Drought at both growth stages significantly altered water relations for both cultivars. Uninfected plants of Janz droughted at tillering had higher total water potential (Ψ) and osmotic potential (π) than diseased plants. However, osmotic potential of droughted controls was lower than diseased plants at anthesis. The number of heads, grain weight and grain number were significantly higher for well-watered than droughted plants and higher for Mulgara than Janz. The controls (38%) had significantly less lesioned roots than 'Pythium' (53%) and 'Rhizoctonia' (50%) and root lesion percentage in Janz was significantly higher than Mulgara except in the 'Rhizoctonia' treatment. In conclusion, the pathogens affected water use during tillering but not at later stages when roots developed beyond the inoculation point.