Award details

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

Reference	BB/K018167/1
Principal Investigator / Supervisor	Dr Tim George
Co-Investigators / Co-Supervisors	Dr David Lumsdon, Dr Charles Shand, Professor Marc Stutter
Institution	The James Hutton Institute
Department	Ecological Sciences
Funding type	Research
Value (£)	434,085
Status	Completed
Type	Research Grant
Start date	27/01/2014
End date	26/01/2017
Duration	36 months

Abstract

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.

Summary

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 economicallyand 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.

Impact Summary

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-plantsystem, 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.

Committee	Research Committee B (Plants, microbes, food & sustainability)
Research Topics	Crop Science, Plant Science, Soil Science
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

Associated awards:

BB/K017047/1 Exploiting root exudation of organic acids and phytases to enhance plant utilisation of soil phosphorus

BB/K018795/1 Exploiting root exudation of organic acids and phytases to enhance plant utilisation of soil phosphorus

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