Exploiting plant root exudation of organic acids and phytases to enhance plant utilisation of soil organic phosphorus

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Organic phosphorus is a common constituent of the P in many soils and comprises mostly of esters of fully oxidised P where P is attached to C through an O atom. Other compounds such as phosphonates and organic polyphosphates occur in lesser amounts. Our appreciation of the extent to which crop plants can utilise organic P pools in soils is limited. The overarching aim of the project is to test the hypothesis that: Cropping systems with roots exuding both organic acid anions and phytase can facilitate more sustainable agricultural production by accessing soil organic P forms.

We will investigate and attempt to understand the role of organic acid anions and phosphatases in exemplar plant mixtures in accessing organic P in soils. We shall then explore what happens to these compounds in the soils and the rhizosphere. A range of experiments will be carried out to identify potentially suitable strains of barley and clover for such a system, followed by experiments incorporating different combinations of these strains, grown in soil, to assess what combinations can most efficiently access different forms of organic P, while minimizing the losses of P via leachate. Experiments and techniques employed will include screening of plant populations for abilities to exude organic acids and phosphatases using anion exchange resins (AERs) and DGT (diffusive gradients in thin films), HPLC, enzyme hydrolysis and 31P nuclear magnetic resonance (NMR) analysis, for identification of organic P compounds and groups in soil extracts and soil water.

Phosphorus (P) is a non-renewable resource crucial to past and future agricultural productivity. The primary source of P fertiliser is mineral deposits, with 85% of the global resource being located in Morocco and Western Sahara. This concentrated geographical distribution means that global food security is threatened not only by finite supplies of rock phosphate fertiliser, but also through potential geopolitical instability. Therefore growing concerns for food security necessitate an improvement in agronomic P efficiencies, based on sound knowledge of the range and quantities of P forms in soils. This proposed project will explore technologies to improve crop productivity and nutrient use efficiency by enhancing the availability to plants of organic P in soils (which is relatively unavailable, but plentiful), whilst also minimising any potential negative environmental consequences. It therefore potentially has implications for anyone involved in crop production from agricultural research scientists, fertiliser suppliers, crop breeders, land managers through to policy makers. Knowledge of organic P species in soils is fundamental to the development of new plant varieties able to hydrolyse the organic P resources which may occur in different soil types and therefore this project is of particular interest to plant breeders. Additionally, it will assist with development of cropping techniques such as bi-cropping for maximisation of the benefits of different plant traits. A plant combining approach that increases P acquisition may be readily adopted into grassland and fodder agriculture and subsequently ways found to allow extension to intensive arable systems. This could be realised by the use of plant molecular genetics to allow both exudation of low molecular weight organic acid anions and enzymes in cereal crop varieties. It would become viable to explore these different agronomic application options once the grounding work on organic P release from the soil-plant system, as contained in this proposal, is completed.

Ultimately this work could potentially inform policy through providing information on how to maximise crop yields while minimising fertiliser inputs. Results could influence the way in which cropping systems are considered in the future, providing some fundamental science supporting their development, based on more than just yield/productivity, but also on the specific soil/plant processes involved. In the long term this work could contribute to the nation's wealth by providing guidance on more nutrient efficient cropping techniques and indicating which traits in plants should be developed, and how they may work in tandem to maximise productivity while minimising fertiliser usage. It may also mean that the nation becomes less reliant on the increasingly scarce global mineral P resources, which are not only becoming more expensive, but also in a time of political instability, could potentially become inaccessible. The basic principle behind the science proposed here is relatively simple to convey, and in combination with its strategic importance to BBSRC with regard to Food Security, makes it an ideal topic to showcase to the public. This will be done at all the participating Institutes' Open days/School Science Week events, meaning it would not only have benefits to the current scientific community, but may also stimulate a new generation of scientists into this field of research. This project addresses the BBSRC strategic research priority areas of crop science (food security) and global security. The project team have direct access to avenues for dissemination of the science into policy through the EA/DEFRA Demonstration Test Catchments, the SEPA Diffuse Pollution Management Advisory Group and the JHI Centres of Expertise for Waters.