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C Corresponding author on soil and geomorphological issues; email: wverboom@agric.wa.gov.au D Corresponding author on botanical issues.Abstract. This communication presents the hypothesis that certain Australian lateritic and related oligotrophic soils may have been partly derived biotically from soluble iron-rich complexes generated following secretion of lowmolecular weight organic acids by phosphate-absorbing specialised proteoid (cluster) roots of proteaceous plants. Subsequent precipitation of the iron is then pictured as occurring onto the oxide rinds of developing laterite after consumption of the organic components of the complexes by soil bacteria. The hypothesis is first examined in relation to current theories of origins of laterites and the extent of the coincidences worldwide in past and present times between Proteaceae and oligotrophic soil types of lateritic character. The paper then provides more definitive lines of evidence supporting the hypothesis, based largely on recent studies by the authors in south-western Western Australia. This relates to (a) cases of definitive association in habitats rich in Proteaceae between zones of root proliferation and ferricrete layers in lateritic soils, (b) proximity in soil profiles between ferric deposits and current and ancestral root channels, (c) the recovery of citrate-consuming bacteria from soil profiles and specifically from ferricrete rinds and horizons accumulating sesquioxide organic matter and (d) distribution of iron and phosphorus within plant and soil profile components consistent with ferricrete rinds being generated by rhizosphere-mediated interactions of plants and microbes under conditions of severely limited availability of phosphorus. The mode of functioning of proteoid root clusters is then discussed, especially in relation to exudation of organic acid anions, uptake of phosphorus and the subsequent fate of organic anions and their metal ion complexes in the system. An empirically based scheme is presented indicating flow profiles for phosphorus and iron between soil, ferricrete rinds and bacterial and plant components. We then discuss possible carbon costs to proteaceous plant partners when accessing phosphorus under the nutrient-impoverished conditions typical of heathlands and open woodlands of Mediterranean-type ecosystems of Western Australia. The paper concludes with a critical overview of the hypothesis, particularly its implications regarding possible higher plant: microbial influences shaping soil and landscape evolution in the regions involved. J . S . P a t e , W . H . V e r b o o m a n d P . D . G a l l o w a y B T 0 0 0 8 6 I n t e r r e l a t i o n s h i p s b e t w e e n P r o t e a c e a e a n d l a t e r i t e s J . S . P a t e e t a l . e t a l .

Clay pavements formed by eucalypts have pronounced effects on understorey vegetation and may have been instrumental in establishment of the complex mosaics of mallee-woodland and proteaceous heathland observed across semi-arid landscapes of south-west Western Australia. Findings are related to earlier observations on the range of plant-mediated changes in soil profiles discussed in the recently advanced 'Phytotarium' concept.

This review draws attention to information from the literature and our own observations supporting the view that higher plants and micro-organisms display an intrinsic capacity to be proactively involved in pedogenetic processes. 'Bioengineering' of this kind is deemed to be spearheaded by principal deep-rooted tree and shrub species and to result in optimisation of command and conservation of water and nutrients within an ecosystem. Specific examples discussed in the paper include, the formation of silicon-or iron-based linings of vertical channels and pores, binding of sand on roots, generation of organically derived hydrophobicity, development of clay-based hardpans and texture-contrast seals, precipitation of silcrete, calcrete and ferricrete pavements, effective accessing and conservation of P resources, including mining by microbes and the biological cycling of Si and Al via plants and micro-organisms. In each case, definitive roles and mechanisms are suggested for the organisms involved, particularly in relation to formative effects relating to secretion of organic acids, dispersing agents and other classes of exudate. We introduce the term 'phytotarium' to connote the collective outcomes of the above biotic influences in construction and maintenance of niches peculiar to specific vegetation types and then review the evidence of imprinting of soil profiles due to operation of phytotaria. Examples given relate to the lateral and vertical facies encountered in certain contemporary soil profiles and paleosols with which we are familiar and are described in a companion paper.