Phosphorus cycling in the soil-microbe-plant continuum of agri-ecosystems

元素磷(P)是作物确保良好生长和产量所必需的营养素。作物通过根系以磷酸盐的形式从土壤中获取磷（一个磷原子被四个氧原子包围，Pi）。作物在土壤中获得π的有效性取决于土壤类型、pH值、土壤中细菌和真菌的生长以及作物吸收π的量。不幸的是，磷具有很强的活性，可以与其他元素或有机化合物一起被锁在土壤中，这使得作物很难获得足够的磷。为了克服这个问题，农民们在作物中添加了Pi肥料。然而，磷肥是由不可再生资源磷矿制成的，在未来几十年，磷矿的可用性将下降，价格将上涨。过度使用磷肥也是一个问题，因为磷肥可能被冲入当地的河流和湖泊，并导致富营养化过程。由于植物在没有Pi肥料的情况下进化了数百万年，它们很好地适应了环境，以帮助提高根部附近Pi的可用性。在培育作物品种时，许多这些适应性并没有被直接选择，或者它们没有被优化用于快速生长的高产作物。这些适应包括长出更多的根，从根中释放酸，将Pi释放到土壤中，从根中释放酶，释放被有机化合物困住的Pi，招募土壤细菌和真菌来帮助获得Pi。为了减少我们对Pi肥料的需求，我们将研究这些植物的适应性和生长在油菜根部附近的细菌。我们将首先使用下一代测序技术识别生活在这些作物根部附近的细菌。这使我们能够对生活在根部附近土壤中的大多数细菌的基因组进行测序并识别它们。我们还将研究细菌和根产生的酶和蛋白质。这些方法将告诉我们根部附近土壤中的细菌活动，以及它们对哪些过程起作用。由于磷在土壤中可以以不同的形式存在，例如与土壤结合或被困在有机化合物中，我们将使用31P-NMR波谱来研究磷的形式及其变化方式。作物根部周围细菌的生长在很大程度上受根部释放的糖和其他产物的控制；这些物质的含量和浓度是由基因决定的。我们将减少一些决定这些化合物释放的基因的表达，并研究它们对根系附近细菌类型的影响，以及它们对磷有效性的影响。最后，作物对磷的需要量在生长季节变化，在收获季节下降。我们将研究根系及其附近生长的细菌如何随着时间的推移而变化，并调节作物对磷的可利用性。这些研究将为作物如何控制生长在其根部附近的细菌、细菌如何帮助作物获得磷以及这些过程在生长季节如何变化提供有价值的信息。这些信息将有助于开发农业系统，更有效地利用土壤中现有的磷，并优化种植成功作物所需的磷肥量。它还将为培育更有效地从土壤中获取Pi的作物提供目标，这些作物要么自己获取，要么借助一些土壤细菌的帮助。

The element phosphorus (P) is an essential nutrient required by crops to ensure good growth and yields. Crops get their P from the soil via their roots in the form of phosphate (a phosphorus atom surrounded by four oxygen atoms, Pi). The availability of Pi for the crop in the soil depends on the soil type, its pH, the growth of bacteria and fungi in the soil and the amount of Pi the crop takes up. Unfortunately, P is very reactive and can get locked away in the soil either with other elements or in organic compounds, making it hard for the crop to acquire sufficient Pi. To overcome this, farmers add Pi fertilisers to the crop. However, Pi fertilisers are made from rock phosphate, a non-renewable resource, the availability of which is set to decline, and the price increase, over the coming decades. Excessive use of Pi fertilisers is also a problem as the Pi can be washed into local rivers and lakes and contributes to the process of eutrophication. Since plants evolved over millions of years without Pi fertilisers, they are well equipped with adaptations to help improve the availability of Pi near their roots. Many of these adaptations have not been selected for directly when breeding crop varieties or they are not optimised for rapidly growing, high yielding crops. These adaptations included making more roots, releasing acids from their roots to free Pi bound to the soil, releasing enzymes from their roots to release Pi trapped in organic compounds and recruiting soil bacteria and fungi to help acquire Pi. To help reduce our need for Pi fertilisers we will study these plant adaptations and the bacteria that grow near the roots of oilseed rape. We will begin by identifying the bacteria that live near the roots of these crop plants using next generation sequencing technology. This allows us to sequence the genomes of most of the bacteria living in the soil near the roots and identify them. We will also investigate the enzymes and proteins made by the bacteria and the root. These approaches will tell us about bacterial activity in the soil near the root and which processes they are contributing towards. Since the P can be in different forms in the soil, such as bound to the soil or trapped in organic compounds, we will use 31P-NMR spectroscopy to investigate what forms the P is in and how they change.The growth of bacteria around the roots of the crop is largely controlled by sugars and other products released by the roots; the content and concentrations of these are genetically determined. We will reduce the expression of some of the genes that determine the release of these compounds and study the effects on the types of bacteria present near the roots and the processes they affect in relation to P availability.Finally, the P requirement of the crop changes during the growing season, declining towards harvest. We will study how the root and the bacteria growing near to it change overtime and regulate the availability of P to the crop.These studies will provide valuable information on how a crop controls the bacteria growing near its root, how the bacteria help the crop acquire P and how these processes change during the growing season. This information will help develop agricultural systems that use existing P in the soil more efficiently and optimise the amount of Pi fertiliser required to grow a successful crop. It will also provide targets for breeding crops that are more efficient at acquiring Pi from the soil, either by themselves, or with help from some soil bacteria.