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As part of a general soil and regolith mapping exercise across cleared and remnant bush land, radiometric data for distribution of potassium (K), uranium (U) and thorium (Th) were examined alongside relief models and floristic and soil surveys in test catchments at Elashgin and Toolibin in the Western Australian wheat-belt. The Elashgin survey showed that highly weathered low K soils co-concentrated U and Th and were vegetated mainly by cluster root-bearing Proteaceae and Casuarinaceae. In granitic soils ratios of U to Th were higher and cluster root bearing taxa much less prominent, except where ferricrete gravels were concentrated. Draping of radiometric imagery over a digital elevation model showed spiral waveforms of high and low U and Th signal which were largely independent of topography but demarcated different oligotrophic communities. General observations and a detailed 900-m transect along an aeolian sand plume at Toolibin showed very high U and Th in ferricrete gravels where Proteaceae were dominant, but failed to separate proteaceous versus myrtaceous shrublands on deep sands due to truncation of signal. Augering along the transect and examination of floristic, soil and signal composition of 32 sites in the Lake Toolibin catchment confirmed presence and degree of development of ferricretes in the rhizosphere of Proteaceae-dominated communities and showed high reactivity scores for Al in `Bs' horizons in profiles carrying such vegetation. Highly specific associations between Proteaceae and very high U and Th were generally evident on exposed ferricrete gravels. The data are discussed in relation to the effects of root exudates on ferricrete formation and destruction and how the broader spatial pattern of such processes might relate to competition for soil phosphorous. [ABSTRACT FROM AUTHOR]

Background and Aims: Previous studies have described the laying down of specific B horizons in south-western Australian ecosystems. This paper presents biomolecular, morphological and physicochemical analyses elucidating the roles of specific woody plant taxa and rhizosphere bacteria in producing these phenomena., Methods: Clayey deposits within lateral root systems of eucalypts and appropriate background soil samples were collected aseptically at multiple locations on sand dunes flanking Lake Chillinup. Bacterial communities were profiled using tagged next-generation sequencing (Miseq) of the 16S rRNA gene and assigned to operational taxonomic units. Sedimentation, selective dissolution and X-ray diffraction analyses quantitatively identified clay mineral components. Comparisons were made of pedological features between the above eucalypt systems, giant podzols under proteaceous woodland on sand dunes at the study site of Jandakot and apparently similar systems observed elsewhere in the world., Key Results: Bacterial communities in clay pods are highly diverse, resolving into 569 operational taxonomic units dominated by Actinobacteria at 38.0-87.4 % of the total reads. Multivariate statistical analyses of community fingerprints demonstrated substrate specificity. Differently coloured pods on the same host taxon carry distinctive microfloras correlated to diversities and abundances of Actinobacteria, Acidobacteria, Firmicutes and Proteobacteria. A number of these microbes are known to form biominerals, such as phyllosilicates, carbonates and Fe-oxides. A biogenic origin is suggested for the dominant identified mineral precipitates, namely illite and kaolinite. Comparisons of morphogenetic features of B horizons under eucalypts, tree banksias and other vegetation types show remarkably similar developmental trajectories involving pods of precipitation surrounding specialized fine rootlets and their orderly growth to form a continuous B horizon., Conclusions: The paper strongly supports the hypothesis that B-horizon development is mediated by highly sophisticated interactions of host plant and rhizosphere organisms in which woody plant taxa govern overall morphogenesis and supply of mineral elements for precipitation, while rhizosphere microorganisms execute biomineralization processes., (© The Author(s) 2019. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)