A field-based project was undertaken to develop and test a mechanism which would allow for the correlation of the health of vegetation surrounding playa lakes in south-west Australia with the natural variation in salinity and waterlogging that occurs spatially and temporally in natural systems. The study was designed to determine threshold ranges of vegetation communities using moderately extensive data over short temporal periods which will guide the design of potential engineering solutions that manipulate hydrological regimes to ultimately conserve and protect native vegetation. A pair of playa lake ecosystems, surrounded by primary production land, was modelled with hydro-geological data collected from March 2006 to March 2007. The data was used to determine the hydroperiods of vegetation communities fringing playa lakes and provide insight into the areas and species that are most affected by extreme rainfall events which are hypothesised to have a significant, rapid deleterious effect on the ecosystems. The methodology was multi-faceted and included; a detailed topographical survey; vegetation surveys; hydrological and hydro-geological monitoring over a 12 month period. 4 The hydro-geological data and vegetation data was linked with the topographical survey at a high resolution for spatial analysis in a Geographic Information System (GIS) to determine the degree of waterlogging experienced by vegetation communities over the monitoring period. The study has found that the spatial and temporal variability of hydroperiods has been reduced by rising groundwater levels, a result of extensive clearing of native vegetation. Consequently populations are becoming extinct locally resulting in a shift in community composition. Extreme summer rainfall events also have a significant impact on the health of vegetation communities by increasing the duration of waterlogging over an annual cycle and in some areas expanding the littoral zone. Vegetation is most degraded at lower positions in the landscape where communities are becoming less diverse and dominated by salt tolerant halophytic species as a result of altered hydrological regimes. Some species appear to be able to tolerate groundwater depths of less than 2.0 m from the surface, however there are thresholds related to the duration at which groundwater is maintained at this depth. Potential engineering solutions include groundwater pumping and diverting water through drains to maintain sustainable hydroperiods for vegetation in areas with conservation value. The effectiveness and efficiency of the engineering solutions can be maximised by quantifying thresholds for vegetation that include sustainable durations of waterlogging. The study has quantified tolerance ranges to salinity and waterlogging with data collected over 12 months but species may be experiencing a transition period where they have 5 sustained irreversible damage that will result in their eventual mortality. With long-term monitoring, the methodology developed and tested in the study can be used to quantify the long-term tolerance ranges that are important for the application of conservation approaches that include engineering solutions.

[Truncated abstract] In southern Australian farming systems the replacement of deep-rooted perennial native vegetation with shallow-rooted annual crops and pastures has resulted in rising groundwater tables and an increased incidence of dryland salinity. It has been suggested that to address this issue by restoring hydrological balance, large areas of agricultural land need to be vegetated with perennial plants. One of the most agriculturally productive ways to do this is to introduce perennial pastures, both into upslope groundwater

[Truncated abstract] The hydraulic properties of the roots of three crop species important to Western Australia were examined: wheat (Triticum aestivum), narrow-leafed lupin (Lupinus angustifolius) and yellow lupin (L. luteus). Generally, the hydraulic conductivity (Lpr) of root systems differs between species and can change in response to adverse conditions. To determine the significance of root anatomy and aquaporin activity on the pathway of water flow through roots, water flow was measured across cell membranes, individual roots and whole root systems. The combination of measurements identified that wheat and lupin roots have contrasting hydraulic properties. Wheat roots absorb water preferentially in the apical region, whereas lupin roots appear to absorb water more evenly along the entire root length. Lupin roots have a greater axial hydraulic conductance than wheat, due to more abundant xylem vessels and axial conductance increases with root length, in conjunction with xylem vessel development. However, water flow through the radial pathway is the limiting factor in whole root hydraulic conductance, in all species. Modelling and the inhibition of aquaporin activity with mercuric chloride demonstrated that radial water flow in wheat roots occurs by a combination of the cell-to-cell and apoplastic pathways, but in lupins, water flow appears to be predominantly apoplastic. Despite the presence of aquaporins in root cell membranes of all species, their role in regulating bulk water flow across roots is not clear in lupins, because of the significance of the apoplastic pathway ... After draining the chambers, the root systems of yellow lupin resumed growth, but there was no subsequent recovery in narrow-leafed lupin root systems. The growth and survival strategies of wheat and lupin root systems are disparate. Wheat root systems are comprised of numerous fine, highly branched, individual roots that extract water near the root tips and have the ability to regulate flow. These attributes may be advantageous in non-uniform or variable environments. Moreover, the ability of wheat roots to regulate flow may not only support survival during waterlogging, but also enhance recovery. In comparison, lupin root systems are designed like conduits, for the rapid uptake and transport of water when conditions are favourable. However, their thick taproots and lack of regulation of water transport or anatomical changes make them unsuitable for very wet soils.