Download The contribution of Western Australian native plant species to water

The contribution of Western Australian native plant species to water repellency in Kings Park
Luke Kitchens
Murdoch University
Abstract:
Soil hydrophobicity is reported to vary under different vegetation types, and in different soil environments (e.g.
pH, soil texture, total organic carbon, TOC, and microbial activity). Organic compounds, such as fatty acids and
non-polar waxes, are understood to coat soil surfaces, creating hydrophobic barriers that prevent water
penetration. In this study, links between soil hydrophobicity and a range of Australian native species at a
bushland site in Kings Park, Western Australia, were investigated.
In this talk, I will discuss the main results obtained in the research conducted during my Honours project. Soils
were collected below 6 common species of native Western Australian plants, Eucalyptus marginata (EM),
Banksia attenuata (BA), Jacksonia sericea (JS), Allocasuarina fraseriana (AF), Acacia pulchella (AP) and
Mesomelaena pseudostygia (MP), as well as from patches of bare soil (i.e. control). Repellency (molarity of an
ethanol drop test, MED) as well as 5 soil characteristics (pH, TOC, microbial activity, moisture content and
sand/silt/clay fraction) were measured. Organic compounds were also extracted from soil samples using
sonication, and characterisation (GC-MS) was carried out in order to identify hydrophobic compounds associated
with repellency. The results show that all soil samples collected in this bushland site were water repellent,
ranging from moderate to very severe. Soil hydrophobicity differed significantly (ANOVA) below the different
species (EM soil was the least repellent, MP soil was the most repellent). Microbial activity (CO2 ppm/hr), TOC
(% w/w) and moisture content (% w/w) positively correlated (R Pearson > 0.4, P < 0.001) with MED, however,
linear regression analyses (r2) showed no significant relationships to enable predictability of repellency based on
these soil characteristics. Organic compounds extracted and identified as enhancing soil repellency were long
chain alcohols (≤C29), alkanes (C28), esters (C19 - C23), long chain amides (≤C50) and sterols (C28 - C29).
Continued investigation into these Australian plants and the compounds they release may provide invaluable
information about the causes of soil water repellency. If a particular species is found to induce very severe levels
of repellency in soils beneath it, identifying the types of compounds it releases and the soil environment (e.g.
microbial activity and TOC) it establishes may contribute to a better understanding of the physicochemical
mechanisms that underpin soil water repellency. By studying plant species that induce severe repellency and
their associated compounds, the management of hydrophobic soils can shift from treating the symptoms to
targeting the causes.
Biography:
Luke Kitchens has just completed his Bachelor of Science (Chemistry) with honours at Murdoch University. After
a 10 year career as an educator, Luke decided to study chemistry in order to work in a career that can directly
help the environment. Luke hopes to become a water and soil chemist, and is particularly interested in the
aquatic chemistry of wetlands and natural waters.