Sensitivity of jarrah (Eucalyptus marginata) to phosphate, phosphite, and arsenate pulses as influenced by fungal symbiotic associations

Many plant species adapted to P-impoverished soils, including jarrah (Eucalyptus marginata), develop toxicity symptoms when exposed to high doses of phosphate (Pi) and its analogs such as phosphite (Phi) and arsenate (AsV). The present study was undertaken to investigate the effects of fungal symbionts Scutellospora calospora, Scleroderma sp., and Austroboletus occidentalis on the response of jarrah to highly toxic pulses (1.5 mmol kg−1 soil) of Pi, Phi, and AsV. S. calospora formed an arbuscular mycorrhizal (AM) symbiosis while both Scleroderma sp. and A. occidentalis established a non-colonizing symbiosis with jarrah plants. All these interactions significantly improved jarrah growth and Pi uptake under P-limiting conditions. The AM fungal colonization naturally declines in AM-eucalypt symbioses after 2–3 months; however, in the present study, the high Pi pulse inhibited the decline of AM fungal colonization in jarrah. Four weeks after exposure to the Pi pulse, plants inoculated with S. calospora had significantly lower toxicity symptoms compared to non-mycorrhizal (NM) plants, and all fungal treatments induced tolerance against Phi toxicity in jarrah. However, no tolerance was observed for AsV-treated plants even though all inoculated plants had significantly lower shoot As concentrations than the NM plants. The transcript profile of five jarrah high-affinity phosphate transporter (PHT1 family) genes in roots was not altered in response to any of the fungal species tested. Interestingly, plants exposed to high Pi supplies for 1 day did not have reduced transcript levels for any of the five PHT1 genes in roots, and transcript abundance of four PHT1 genes actually increased. It is therefore suggested that jarrah, and perhaps other P-sensitive perennial species, respond positively to Pi available in the soil solution through increasing rather than decreasing the expression of selected PHT1 genes. Furthermore, Scleroderma sp. can be considered as a fungus with dual functional capacity capable of forming both ectomycorrhizal and non-colonizing associations, where both pathways are always accompanied by evident growth and nutritional benefits

Thermography for characterization of soil water repellency at larger spatial scales

Soil water repellency (SWR) is natural phenomenon occurring in soils throughout the world. It is a surface property that reduces the attraction of soil for water. Measurement of soil water repellency is done at the point scale; however its role in the environment often evaluated at the landscape scale. This disparity is due to limitation in the scale of measurements. The objective of this study is improving characterization of soil water repellency at larger spatial scales through thermography. Thermography shows promise to track the temporal and spatial dynamics of soil water repellency. In a lab experiments, it has been demonstrated that there was a huge potential for thermal imaging in SWR mapping to distinguish between highly repellent areas and wettable ones. However, the proposed technique had a number of limitations. One major drawback was its poor performance to detect low SWR areas which is often present in the environment. Another issue is the induction of a temperature gradient to reveal SWR, while also changing the surface properties of SWR. A strategy to help in distinguishing the differences in SWR is to assess the energy balance and evaporative fluxes of the soil surface. A lab calibration experiment will be presented to distinguish the link between thermal regime, evaporative flux, soil water content and soil water repellency. A field survey using thermography to map soil water repellency at larger spatial scales will improve understanding of how SWR can affect hydrologic processes at larger scales. Through this innovative technique, we will be able to predict and model the behaviour of water dynamics in water repellent soil and therefore improve management of water and soil resources. We will further understand the role soil water repellency plays for ecosystem services

Thermography to assess evaporative fluxes on organic amended water repellent soils

Soil water repellency (SWR) is natural phenomenon occurring in soils throughout the world. It is a surface property associated with the organic composition in soils that reduces the affinity of soil for water. Its impact on ecosystems services are influenced at multiple temporal and spatial scales. Thermography shows promise to detect and track the temporal and spatial dynamics of soil water repellency. In lab experiments, it has been demonstrated that there was a huge potential for thermography in SWR mapping to detect high levels of soil water repellency. However, the technique has a number of limitations. One major drawback was its poor performance to detect low or subcritical levels of water repellency which is often present in the environment. Another issue is the induction of a temperature gradient to reveal SWR, which can change the repellent nature of soil and the evaporative fluxes from soil. The objective of this study is to improve characterization of soil water repellency by examining the change in evaporative fluxes in water repellent soils using thermography. The results from a field experiment with soils amended with organic waste material to increase the level of soil water repellency will be presented. The aim of this study is to distinguish the link between thermal regime, evaporative flux, soil water content and soil water repellency generated by the amendment. Through this approach, we will be able detect difference in evaporative fluxes under organic amended soils and determine the relationship with soil water repellency. This will improve the management of water and soil resources within water repellent soils by understating its effect on water dynamics

Natural attenuation of legacy hydrocarbon spills in pristine soils is feasible despite difficult environmental conditions in the monsoon tropics

The Kimberley region of Western Australia is a National Heritage listed region that is internationally recognised for its environmental and cultural significance. However, petroleum spills have been reported at a number of sites across the region, representing an environmental concern. The region is also characterised as having low soil nutrients, high temperatures and monsoonal rain – all of which may limit the potential for natural biodegradation of petroleum. Therefore, this work evaluated the effect of legacy petroleum hydrocarbons on the indigenous soil microbial community (across the domains Archaea, Bacteria and Fungi) at three sites in the Kimberley region. At each site, soil cores were removed from contaminated and control areas and analysed for total petroleum hydrocarbons, soil nutrients, pH and microbial community profiling (using16S rRNA and ITS sequencing on the Illumina MiSeq Platform). The presence of petroleum hydrocarbons decreased microbial diversity across all kingdoms, altered the structure of microbial communities and increased the abundance of putative hydrocarbon degraders (e.g. Mycobacterium, Acremonium, Penicillium, Bjerkandera and Candida). Microbial community shifts from contaminated soils were also associated with an increase in soil nutrients (notably Colwell P and S). Our study highlights the long-term effect of legacy hydrocarbon spills on soil microbial communities and their diversity in remote, infertile monsoonal soils, but also highlights the potential for natural attenuation to occur in these environments

Cereal phosphate transporters associated with the mycorrhizal pathway of phosphate uptake into roots

A very large number of plant species are capable of forming symbiotic associations with arbuscular mycorrhizal (AM) fungi. The roots of these plants are potentially capable of absorbing P from the soil solution both directly through root epidermis and root hairs, and via the AM fungal pathway that delivers P to the root cortex. A large number of phosphate (P) transporters have been identified in plants; tissue expression patterns and kinetic information supports the roles of some of these in the direct root uptake pathways. Recent work has identified additional P transporters in several unrelated species that are strongly induced, sometimes specifically, in AM roots. The primary aim of the work described in this paper was to determine how mycorrhizal colonisation by different species of AM fungi influenced the expression of members of the Pht1 gene families in the cereals Hordeum vulgare (barley), Triticum aestivum (wheat) and Zea mays (maize). RT-PCR and in-situ hybridisation, showed that the transporters HORvu;Pht1;8 (AY187023), TRIae;Pht1;myc (AJ830009) and ZEAma;Pht1;6 (AJ830010), had increased expression in roots colonised by the AM fungi Glomus intraradices,Glomus sp. WFVAM23 and Scutellospora calospora. These findings add to the increasing body of evidence indicating that plants that form AM associations with members of the Glomeromycota have evolved phosphate transporters that are either specifically or preferentially involved in scavenging phosphate from the apoplast between intracellular AM structures and root cortical cells. Operation of mycorrhiza-inducible P transporters in the AM P uptake pathway appears, at least partially, to replace uptake via different P transporters located in root epidermis and root hairs.Donna Glassop, Sally E. Smith and Frank W. Smit