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

元素磷(P)是农作物确保良好生长和产量所必需的一种营养物质。农作物通过根部以磷酸盐(一个被四个氧原子包围的磷原子，PI)的形式从土壤中获得磷。作物在土壤中对磷的有效性取决于土壤类型、土壤的pH值、土壤中细菌和真菌的生长情况以及作物所占的磷的量。不幸的是，磷是非常活泼的，可以与其他元素或有机化合物一起锁在土壤中，使作物很难获得足够的磷。为了克服这一点，农民们在作物中添加PI化肥。然而，磷化肥是由磷矿制成的，磷矿是一种不可再生的资源，其可用性将在未来几十年内下降，价格将会上涨。磷化肥的过度使用也是一个问题，因为磷可能被冲进当地的河流和湖泊，并导致富营养化过程。由于植物在没有磷化肥的情况下经过了数百万年的进化，它们具有很好的适应能力，以帮助提高根部附近磷的利用率。在育种作物品种时，这些适应中的许多没有被直接选择，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，从根中释放酸来释放与土壤结合的磷，从根中释放酶来释放困在有机化合物中的磷，以及招募土壤细菌和真菌来帮助获得磷。为了帮助减少对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农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排序，并对它们进行识别。我们还将研究细菌和根所产生的酶和蛋白质。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做出了贡献。由于磷在土壤中可能以不同的形式存在，如结合在土壤中或被困在有机化合物中，我们将使用31P-核磁共振光谱来研究磷以什么形式存在以及它们是如何变化的。作物根部周围细菌的生长主要由根部释放的糖和其他产物控制；这些物质的含量和浓度是由遗传决定的。我们将减少一些决定这些化合物释放的基因的表达，并研究它们对根部附近存在的细菌类型的影响，以及它们影响与磷有效性有关的过程。最后，作物的磷需求在生长季节发生变化，到收获时下降。我们将研究根部和生长在根部附近的细菌如何随着时间的推移而变化，并调节作物对磷的有效性。这些研究将提供关于作物如何控制根部附近生长的细菌，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的有价值的信息。这些信息将有助于发展农业系统，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化肥的量。它还将为培育更有效地从土壤中获取PI的作物提供目标，无论是自己还是在某些土壤细菌的帮助下。

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.