Graham O'Hara

The symbiotic performance between legumes and rhizobia relies on the plant-bacteria genetic compatibility and on the symbiotic partner’s capacity to overcome environmental stresses. Symbiosis contributes nitrogen to the plants, which, among other things, increases the number of chloroplasts, and the number and size of cells per leaf. Hyperspectral imagery can detect vegetation changes combining information stored in the image. The symbiotic performance ¡s affected by some abiotic stress factors such as low clay content and low soil water holding capacity. These soil features can be estimated using ground penetrating radar (GPR), a geophysics instrument based on energy pulses interacting with soil layers. The aim of this work was to investigate whether integrated remote sensing techniques are able to estimate the interaction of field pea inoculated separately with five strains of Rhizobium leguminosarum bv. viceae with different nitrogen fixation effectiveness levels. The experiment was carried out firstly in a glasshouse to assess the pure symbiotic performance and then in an agricultural area to assess the interaction with abiotic factors. Hyperspectral images and GPR measurements were captured to cover the glasshouse and field site experiments. The plant sample analyses consisted of plant dry weight, nitrogen content and nodulation score. The plant samples showed significant differences in nitrogen levels, nodule score and dry weight across strains. The analyses of the spectral band combinations confirmed the presence of outstanding indices sensitive to the differential symbiotic performance and were correlated with plant analyses. The GPR data also revealed a mixed composition of soil properties associated with variable water availability that affected root and plant growth. It is concluded that remote sensing can be a valuable tool for estimating legume nitrogen fixation in fields, and GPR for estimating below ground properties that affect plant growth in field experiments.

Exotic pasture legumes and their associated microsymbionts are important in providing biological nitrogen fixation in Australian agricultural systems. Southern African species of Lotononis from the Listia section can potentially provide sustainable agricultural productivity in systems affected by increasing dryland salinity and climate change. There are eight species in the Listia section: L. angolensis, L. bainesii, L. macrocarpa, L. marlothii, L. minima, L. subulata and L. solitudinis (Van Wyk, 1991). They are perennial, stoloniferous and collar-nodulated. The root-nodule bacteria (RNB) isolated from several of these species are pigmented and the symbiosis between these RNB and their hosts is highly specific (Yates et al., 2007). Pioneering work on L. angolensis, L. bainesii and L. listii isolates was performed in Africa in the 1950–60s by Botha (Kenya), Sandman (Zimbabwe) and Verboom (Zambia) and in Australia (Norris, 1958).

Oxidation of ferrous iron by moderately thermophilic species of the genus Ferroplasma is of considerable potential value in commercial bioleaching operations. A collection of strains was enriched and isolated from a number of natural or industrial acidic sites at 45 and 55°C. Phylogenetic analysis based on 16S rRNA gene sequencing indicated that all strains were members of the Order Thermoplasmatales. Stains BH8 and BH12 showed 98% sequence similarity with Ferroplasma acidiphilum strain YT and DR1 respectively. Strains BH7 and BH10 were closely related to the moderately thermophilic species Ferroplasma cupricumulans. Strain BH9, a moderately thermophilic organotroph, was unrelated to previously described species and probably represents a novel genus. Strains BH8 and BH12 showed some unique physiological differences to the type species F. acidiphilum. Unlike F. acidiphilum, both strains were moderately thermophilic with a temperature range for strains BH8 and BH12 of 24 to 61°C and 27 to 49°C respectively. Strain BH12 grew organotrophically on Darland's Medium containing glucose and yeast extract and chemomixotrophically on Darland's Medium supplemented with ferrous sulphate. Moderately thermophilic species of Ferroplasma and Ferroplasma-like genera appear widely distributed geographically and possess considerable physiological and phylogenetic diversity that may benefit industrial bioleaching processes.

Water reclamation is becoming an important option for Australia in the face of increasing pressure on water supplies. A potential concern is the introduction of pathogens into groundwater, especially enteroviruses. Studies on the survival of the enteroviruses poliovirus type 1, coxsackievirus b3 and adenovirus, the bacterial pathogen Salmonella typhimurium and the indicator microorganisms Escherichia coli and MS2 in groundwater have shown a relationship between the presence of indigenous groundwater microorganisms and the survival of the microbial pathogens, and are supported by published results. In the presence of indigenous groundwater microorganisms, pathogens and indicator organisms have shown a greatly reduced survival time. Studies into the conditions and mechanisms behind this observed effect indicated that the presence of indigenous microorganisms was the major influencing factor. Further, they indicate that these microorganisms may be producing compounds (possibly enzymes or other proteins) responsible for the reduced survival. Studies have indicated that these compounds were produced by a small percentage of indigenous groundwater microorganisms and they may be microbial- type specific. Knowledge gained from this study, published work and ongoing investigation could allow for the safer use of reclaimed waters by storage in groundwater aquifers.

Wheat production levels and soil chemical properties on eight paired adjacent fields managed organically and conventionally in Western Australia were monitored and compared in three years (1992-1994). Sites were paired to ensure soil types, crop history before conversion of the organic paddock and, in most cases, the farm managers were the same, so that the management system was the primary object of difference. At four sites (1, 3, 5, 6), the grain yield of organic and conventional wheat was comparable, but grain yield of organic wheat was significantly depressed at the other four sites. The yield depression in the organic plots was most likely related to the lower pre-sowing Colwell-extractable phosphorus level in the soil, later sowing, and low nitrogen supply. In the organic plots, nitrate nitrogen and organic carbon had increased significantly after 2-3 years of pasture in site 3, but Colwell-P and Colwell-K were greatly reduced during this period.