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

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Phosphorus (P) is a non-renewable resource, essential for crop production. Uncertainties over mineral P supplies coupled with concerns for food security and environmental impact of P on waters all necessitate an improvement in agronomic P efficiencies, based on sound knowledge of the range of P forms in soils. Our research is different to previous approaches to recover P from soils in that it focuses on the organic P (Po) components and uses a novel combination of root exudates from different plants to solubilise organic P and make it bioavailable as inorganic orthophosphate.The two fundamental problems associated with the use of soil organic P by plants are that much of it is strongly attached to soil particles and therefore inaccessible to plants, and secondly, even when not firmly attached to soil particles, the forms in which it exists are not readily available for plant uptake. Some plants possess traits that can help access organic P in soils; firstly some plants can produce organic acids from their roots, which can release the P attached to soil particles, and secondly some can release phosphatases (e.g. phytase), which can hydrolyse the organic P into forms which plants can take-up. However, crop plants generally do not possess both these traits and so combinations of plants are required, each carrying out a different role. Systems that rely on clover undersown into cereal crops to provide nitrogen (N) to the current crop, act as an overwinter green manure, and to provide N to following crops are fairly common in organic farming enterprises. We have clover lines which can produce phytase required to mineralize organic P, while some strains of barley have been shown to release organic acids, making the organic P available for mineralisation. We will investigate a clover/barley bi-cropping system as an exemplar sustainable alternative to intensive applications of P and N fertilizers, thus potentially making the arable system more efficient both economically and environmentally. Thus we shall test the overarching 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. Specifically, we propose to investigate and understand the role of organic acids and phosphatases in plant mixtures in accessing the organic P from the inositol phosphate pool. We shall then explore what happens to these organic P forms in the soils and the rhizosphere and examine their potential (or otherwise) for leaching from the soil to surface waters where they may cause eutrophication. 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 leaching losses. By increasing the amount of P utilized from the P stored in soils we can reduce the reliance on inorganic fertilisers, increasing agricultural sustainability and improving our ability to deliver food security in coming decades.