In-soil trophic interactions between plants, rhizosphere bacteria and nematodes: improving availability of soil phosphorus

Phosphorus (P) fertiliser is an important component for agricultural production, but global supplies of rock phosphate are finite and geographically restricted; hence better use of P supplies is vital. Many agricultural soils contain large amounts of P, but mostly in organic forms (especially phytate), which are generally considered unavailable to plants. Some plants can exude both organic acids and enzymes, which together can potentially mobilise and hydrolyse soil organic P. However, the effectiveness of these processes is limited in many soils, and developing systems to utilise these organic P reserves is an important challenge in global sustainable intensification of agriculture. Plant utilisation of P from phytate is improved when inoculated with certain soil micro-organisms. Additionally, it has been demonstrated that below-ground root herbivory by nematodes in grasslands promoted nutrient flux and influenced the composition of the rhizospheric microbial community. Similarly, recent research has shown improved plant utilisation of organic P by pine seedlings when bacterial grazing by nematodes facilitated the release of P from organic sources. Understanding the importance of these soil trophic interactions under arable crops in order to design future sustainable agricultural systems is important for food security. We aim to establish 1) whether trophic interactions between rhizospheric nematode and bacteria increases plant utilisation of P in systems of a range of complexity from agar to soil; and 2) the functional role of plant- and soil bacteria derived enzymes and organic acids and their relative interaction with nematode grazing for enhanced utilisation of organic P.
To achieve this the project will initially include a) controlled environment experiments, growing a range of plants in agar with P supplied in various forms (Pi, phytate and sugar phosphates) with addition of a full factorial combination of bacteria (natural soil community and specific phosphate solubilising bacteria) and nematodes (natural soil community, bacterial grazers and fungal grazers); b) experiments of increasing complexity in soil - soils taken from both treatments of the Balruddery Sustainability Platform (Sustainable vs Conventional) will be sterilised and re-inoculated with an additive range of treatments of increasing complexity. This will include an assessment of the nematode and bacterial community structure assemblages alongside measurement of organic P pools ; c) an assessment of the nematode and bacteria assemblages, alongside measurements of organic P pools in existing treatments of the Rothamsted LTEs and in appropriate samples taken from the archive; d) an internship with the Scottish Government Department Advisory Secretariat to gain an insight into how policy and research interface.