A cross-disciplinary soil-proteomics and modelling approach for predicting switches between hydrophilic and hydrophobic soil surface responses

许多土壤的一个奇怪的特性是它们不容易被雨水湿润，这对土壤管理有许多影响。虽然这些土壤可能不是特别疏水，但润湿速度比从其孔隙大小推断的要慢。这种性质通常被定义为亚临界防水性。在拒水性高（临界拒水性）的情况下，其导致水在土壤表面处的积水。拒水性影响水和溶解或悬浮的化学品通过土壤剖面的排放路线，导致优先地表径流，渗透路径导致严重的侵蚀事件和洪水。土壤斥水性可能受到自然和人为事件的影响。众所周知，加热和干燥的循环（以及许多其他因素）可能会导致土壤性质发生相当大的变化。土壤斥水性是微生物活动和物理化学结构之间相互作用的结果，但它们的复杂性是如此之大，以至于目前它们仅在经验和轶事的基础上被理解。该项目的目的是建立一个理论基础，以了解土壤的防水性，并预测其后果。这种认识的实际影响是深刻和广泛的，因为它们可以指导土地管理做法和防洪。选择研究的三种土壤为：（i）马尔文山粘壤土，在先前的研究中发现，在适度潮湿的夏季条件下以及在实验室中空气干燥后表现出极端的疏水性，（ii）高尔粉壤土，在我们的NERC资助的概念验证蛋白质组学研究中使用，发现显示出中等水平的疏水性，以及（iii）Rothamsted Research Park Grass plot 3粉壤土，目前是大规模土壤宏基因组测序项目“Terragenome”的主题，并且亚临界疏水。土壤含水量将调整至（i）刚好高于和（ii）刚好低于临界土壤含水量，即疏水和亲水行为之间发生转变的含量。进一步的扰动将包括在不同温度下进一步干燥至含水量，以模拟极端干旱时期可能经历的土壤条件，这可能导致疏水性进一步增加，将通过检查不同尺度（从纳米到厘米）的土壤特性来获得与防水性有关的信息。我们将使用元蛋白质组学和特定的疏水蛋白分离方法来建立蛋白质在防水性发展中的作用。原子力显微镜（AFM），最近才应用于土壤颗粒，将用于检查其表面的地理，硬度，粘性和防水性在这个小尺度。该技术与激光扫描显微镜技术相结合，将用于检测荧光染料标记的土壤微生物蛋白质的拒水性。将使用水接触角技术和使用非常小的水滴的渗透时间来检查两个较粗尺度的拒水性。这些对拒水性和土壤颗粒特性的估计将被纳入一个详细的土壤结构计算机模型，该模型将用于预测土壤中分米级拒水性的后果，并将与实验室测量的直径为几厘米的岩心润湿性进行比较。当模型被校准和验证后，我们将能够使用它，与实验数据一起，预测扰动如何改变润湿性。这些影响将被纳入气象局使用的现有气候模型JULES，以便预测气候变化的可能影响。然后，我们将能够建议如何管理英国和其他土壤，以尽量减少径流，侵蚀和洪水风险。

A strange property of many soils is that they do not readily wet on contact with rain, which has many implications for soil management. Although these soils may not be especially hydrophobic, wetting is slower than would be inferred from the sizes of their pores. This property is usually defined as sub-critical water repellency. Where water repellency is high (critical repellency), it causes ponding of water at soil surfaces. Water repellency affects the routes through which water and dissolved or suspended chemicals drain through the soil profile, leading to preferential surface run-off, infiltration paths resulting in serious erosion events, and flooding. Soil water repellency may be influenced by both natural and man-made events. It is known that cycles of heating and drying (amongst many other factors) may produce quite dramatic changes in this soil property. Soil water repellency results from interactions between microbial activity and physico-chemical structure, but their complexity is such that at present they are only understood on an empirical and anecdotal basis. The purpose of this project is to develop a theoretical basis to understand soil water repellency and to predict some of its consequences. The practical implications of such an understanding are profound and widespread, since they may guide land management practice and flood prevention. The three soils selected for study will be; (i) Malvern Hill clay loam, found in a previous study to exhibit extreme hydrophobicity under moderately moist summer conditions and also following air-drying in the laboratory, (ii) Gower silt loam, used in our NERC-funded proof-of-concept proteomics study and found to display up to medium levels of hydrophobicity, and (iii) Rothamsted Research Park Grass plot 3 silt loam, presently the subject of the large-scale soil metagenomic sequencing project 'Terragenome', and subcritically hydrophobic. Soil water content will be adjusted to (i) just above and (ii) just below the Critical Soil-water Content, i.e. the content at which there is a transition between hydrophobic and hydrophilic behaviour. Further perturbations will include further drying at different temperatures to water contents simulating soil conditions that may be experienced during extreme drought periods, which are likely to cause further increases in hydrophobicity.Information relating to water repellency will be obtained by the examination of soil properties at various scales of size (from nanometres to centimetres). We will establish the role of proteins in the development of water repellency using metaproteomics and specific hydrophobic protein isolation approaches. Atomic force microscopy (AFM), only recently applied to soil particles, will be used to examine their surface geography, hardness, stickiness and water repellency at this small scale. This technique combined with laser scanning microscopic techniques will be used to examine the water repellency of soil microbial proteins labelled with fluorescent dyes. Water repellency at two coarser scales will be examined using a water contact angle technique and penetration times using very small drops of water. These estimates of water repellency and soil particle properties will be incorporated into a detailed computer model of soil structure, which will be used to predict the consequences of water repellency at the decimeter scale in soil, and will be compared with laboratory measurements of the wettability of cores of a few centimeters in diameter. When the model is calibrated and validated, we will be able to use it, together with the experimental data, to predict how the perturbations change wettability. These effects will be incorporated into an existing climate model used by the Met Office, called JULES, so that predictions can be made about the likely effect of climate change. Then we will be able to suggest ways to manage UK and other soils to minimize run-off, erosion and flood risk.