Plant-based controls on soil structural dynamics: elucidating the interactive roles of the genotype, phenotype and soil microbial community

只有土壤具有适当的结构，集约生产系统才能成功地生产足够多的优质作物。这种结构是由土壤矿物质颗粒和有机质相互作用形成的。土壤中的生物，特别是植物的根，在这一过程中发挥着重要的作用。没有良好的土壤结构，土壤就不能为植物提供足够的水分，根系就不能发育，养分就会流失，降雨进入土壤的入渗量就会减少，从而导致洪水和侵蚀。在集约化作物生产下，由于过度耕作，通常是由于更大、更重的机械、土壤有机质的损失和极端天气事件，土壤结构普遍丧失。在维持生产的同时，迫切需要改善和保持良好的土壤结构。要做到这一点，选择有限，而要想取得成功，很可能需要在广泛的战线上使用各种方法。减少耕作作业、进行残渣管理以增加有机质含量以及种植适当的覆盖作物是可能的策略。后者是有效的，因为植物直接通过根部的机械作用改变土壤结构，间接地通过促进土壤中其他生物的活动来实现。然而，覆盖作物一般只在土壤中停留相对较短的时间，因此其可能的效力有限。人们很少注意到使用主要作物品种的可能性，因为这些品种具有特殊的能力来设计良好的土壤结构。这将比使用覆盖作物更好，因为在整个作物生长过程中，土壤结构将随着水分和养分的利用效率和土壤生物多样性的提高而得到改善。我们知道作物种类内根系的大小和结构有相当大的差异，但我们不知道植物设计土壤结构的能力是否有相应的变化，以及与这些根系相互作用的土壤结构的动态。这就是这个项目要解决的问题。我们建议研究一系列已知具有非常不同的根系特性的小麦植物，并检查它们穿透压实土壤的能力，并通过与土壤微生物的相互作用来促进土壤团聚体的发展，这些微生物也发挥着生物工程的作用。我们将在土壤结构以不同方式退化的受控实验系统中种植这些植物。我们将利用X射线计算机断层扫描技术，直观地显示根的三维分布、它们穿透压实土壤的能力，以及它们如何促进健全的土壤结构的发展。这将在整个根系的尺度上完成，但也在紧邻根部(根圈)的精细尺度(千分之一毫米)上完成。为了做到这一点，我们将采用和发展数学方法来分析复杂的空间变异性，并使用这些方法来模拟根系如何改变土壤结构的局部变化。这些方法将描述根系及其周围环境的特性。我们对所使用的植物的遗传背景有详细的描述。遗传分析方法可以用来显示生物体的特性在多大程度上取决于该生物体基因组中的特定元素，这对于说明如何针对这些特性来选择和培育具有增强特性的新品种是至关重要的。我们将使用这些方法，但我们将检查的属性将不仅限于植物本身，还将包括工厂工程师如何改善周围土壤结构的措施。因此，我们将展示如何培育小麦植株，以改善种植它们的土壤结构和生产系统的可持续性。

The production of sufficient good quality crops from intensive production systems can be successful only if the soil has an appropriate structure. This structure is created by interactions between soil mineral particles and organic matter. Organisms in soil, in particular the roots of plants, play an important role in this process. Without good soil structure the soil cannot supply adequate water to plants, root systems cannot develop, nutrients are lost and infiltration of rain fall into soil is reduced resulting in floods and erosion. There has been a general loss of soil structure under intensive crop production, resulting from excessive tillage, often by larger and heavier machinery, the loss of soil organic matter and extreme weather events.It is an urgent necessity to improve and maintain good soil structure, while sustaining production. There are limited options for doing this, and it is likely that success will require a variety of approaches used across a broad front. Reducing tillage operations, residue management to increase organic matter content, and growth of appropriate cover-crops are possible strategies. The latter can be effective because plants 'engineer' soil structure, both directly through the mechanical action of roots, and indirectly by promoting the activity of other organisms in soil. However, cover crops are generally only in the soil for relatively short periods and their likely effectiveness thus limited. Little attention has been given to the possibility of using main crop varieties which have a particular capacity to engineer good soil structure. This would be better than use of cover crops because soil structure would be promoted, along with water and nutrient-use efficiency and soil biodiversity, throughout the period of crop growth.We know that there is considerable variation in the sizes and architecture of root systems within crop species, but we do not know whether there is corresponding variation of the capacity of the plant to engineer soil structure, and the dynamics of soil structure in interaction with these root systems. That is the question to be addressed in this project. We propose to study the a wide range of wheat plants known to have very different root properties and to examine their ability to penetrate compacted soil and to promote the development of soil aggregation through interactions with soil microbes that are known also to play a 'bioengineering' role.We will grow such plants in controlled experimental systems in which the soil structure is degraded in different ways. We will visualise the 3-dimensional distribution of roots, their ability to penetrate compacted soil, and and how they promote the development of a sound soil structure using X-ray computed tomography. This will be done at the scale of the whole root system, but also at fine scale (thousandths of a mm) in the immediate vicinity of the roots (the rhizosphere). To do this we shall adapt and develop mathematical methods to analyse complex spatial variability, and use these to model how the root modifies the local variation of soil structure. These methods will characterize the properties of root systems, and their immediate surroundings. We have a detailed characterisation of the genetic background of the plants that are used. Methods of genetic analysis can be used to show the extent to which properties of an organism depend on particular elements in that organism's genome, which is essential for showing how those properties can be targeted for selection and breeding of new varieties with enhanced properties. We shall use these methods, but the properties we shall examine will not be confined to the plants themselves, but will include measures of how the plant engineers improved structure in the surrounding soil. We shall therefore show how wheat plants can be bred to improve the structure of soils in which they are grown and the sustainability of the production system.