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

磷是一种不可再生资源，对作物生产至关重要。矿物磷供应的不确定性，加上对粮食安全和磷对水的环境影响的担忧，都需要基于对土壤中磷形态范围的充分了解，提高农业磷效率。我们的研究不同于以往从土壤中回收磷的方法，因为它侧重于有机磷（Po）成分，并使用不同植物根系分泌物的新组合来溶解有机磷，使其成为无机正磷酸盐。与植物利用土壤有机磷有关的两个基本问题是，大部分有机磷强烈附着在土壤颗粒上，因此植物无法获得；其次，即使不牢固地附着在土壤颗粒上，它存在的形式也不容易被植物吸收。有些植物具有有助于获取土壤中有机磷的特性；首先，有些植物可以从根部产生有机酸，释放附着在土壤颗粒上的磷；其次，有些植物可以释放磷酸酶（如植酸酶），将有机磷水解成植物可以吸收的形式。然而，农作物通常不具备这两种特性，因此需要植物的组合，每一种都发挥不同的作用。在有机农业企业中，依靠三叶草播种到谷类作物中，为当前作物提供氮(N)，作为越冬绿肥，并为后续作物提供氮的系统相当普遍。我们有三叶草系列，可以产生矿化有机磷所需的植酸酶，而一些大麦品种已被证明可以释放有机酸，使有机磷可用于矿化。我们将研究三叶草/大麦双作系统，作为磷和氮密集施用的可持续替代范例，从而有可能使耕地系统在经济和环境上更有效。因此，我们将测试一个总体假设：根系同时散发有机酸阴离子和植酸酶的种植系统可以通过获取土壤有机磷形态来促进更可持续的农业生产。具体来说，我们建议研究和了解植物混合物中有机酸和磷酸酶在从肌醇磷酸池中获取有机磷方面的作用。然后，我们将探索这些有机磷在土壤和根际中发生了什么变化，并检查它们从土壤淋滤到地表水的潜力（或其他），在那里它们可能导致富营养化。将进行一系列实验，以确定可能适合这种系统的大麦和三叶草菌株，随后将这些菌株的不同组合进行实验，在土壤中种植，以评估哪种组合可以最有效地获取不同形式的有机磷，同时最大限度地减少淋失。通过增加土壤中磷的利用率，我们可以减少对无机肥料的依赖，增加农业的可持续性，提高我们在未来几十年提供粮食安全的能力。

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.