Soil surface matters: Microbial controls upon hydraulic behaviour at the soil surface

土壤是陆地功能的基础，并通过其提供的一系列商品和生态系统服务（包括粮食生产、水储存和过滤以及支持生物多样性）支撑着人类文明。土壤表面是一个至关重要的区域，因为它是降雨或灌溉水与下层土壤之间的第一个接触点。土壤表面的性质，例如孔隙度、结构弹性或疏水性，会影响水进入土壤基质（从而被储存并供植物使用）或流失（可能导致土壤侵蚀、水道污染和洪水增加）的程度。一些具有商业价值的土壤在降雨/灌溉条件下容易在地表发生团聚体破裂，导致形成封条和帽状，从而影响作物出苗，影响产量和质量，并显著减少入渗。虽然对该区域涉及的物理化学过程进行了广泛的研究，但很少考虑微生物在影响耕地和园艺系统中土壤表面发生的关键过程中所起的作用，特别是在英国。众所周知，土壤生物通过多种机制来创造、破坏和改变土壤结构和疏水性。然而，直到最近，人们才发现极端土壤表面的生物与深层土壤带的生物有很大的不同，因此，土壤生物群对控制表层土壤和水的相互作用的贡献需要更好地理解。我们建议量化不同类型的土壤微生物影响降雨与直接土壤表面的结构和水文特性之间相互作用的程度。我们将通过实验控制哪些生物在土壤表面的微生物群落中占主导地位，应用模拟降雨，测量土壤结构，水渗透土壤的程度，土壤排斥水的程度以及发育表面的物理强度来实现这一目标。我们将包括由农民管理的土壤，以促进重新聚集和结构完整性，从而导致不同微生物群落的存在。我们还将研究降雨的强度和动能如何影响这些现象，这对于理解气候变化将影响风暴以及影响土壤表面的单个雨滴的能量是很重要的。据预测，气候变化会增加降雨强度，但目前我们还不知道土壤管理将如何影响这种生物和物理相互作用。这项研究的结果将告诉我们土壤微生物群落如何影响土壤表面的性能，并为设计更有效和可持续地管理土壤系统的方法提供必要的基础知识。

Soils are fundamental to terrestrial function, and underpin human civilisation by virtue of the range of goods and ecosystem services they provide, including food production, water storage and filtration, and supporting biodiversity. The soil surface is a crucially important zone since it is the first point of contact between rainfall or irrigation water and the underlying soil. The nature of the soil surface, for example in terms of porosity, structural resilience or hydrophobicity, affects the extent to which water enters the soil matrix (and thus is stored and available to plants) or runs off (potentially leading to soil erosion, pollution of waterways and increased flooding). Some commercially significant soils are prone to aggregate breakdown at the surface under rainfall/irrigation, leading to the formation of seals and caps which can impair crop emergence, affecting both yield and quality and significantly reduce infiltration. Whilst there has been extensive research into the physico-chemical processes involved in this zone, there has been remarkably little consideration of the role that micro-organisms play in affecting key processes occurring at the soil surface in arable and horticultural systems, particularly in the UK context. Soil organisms are known to create, destroy and modify soil structure and water-repellency by a number of mechanisms. However it is only recently that is has been revealed that the biology of the extreme soil surface is rather different to that which occurs in deeper soil zones, and hence the contribution of the soil biota to governing soil:water interactions at the surface needs to be better understood.We propose to quantify the extent to which different types of soil micro-organisms affect the interactions between rainfall, and the structural and hydrological properties of the immediate soil surface. We will achieve this by experimentally manipulating which organisms dominate the microbial community at the soil surface, applying simulated rainfall, and measuring soil structure, the extent to which water infiltrates the soil, how much the soil repels water, and the physical strength of developed surfaces. We will include soils which have been managed by farmers to promote re-aggregation and structural integrity in ways which lead to different microbial communities being present. We will also study how the intensity and kinetic energy of rainfall affects these phenomena, which is important to understand since climate change will affect both storm as well as the energies of individual raindrops impacting the soil surface. Climate change is predicted to increase rainfall intensity, but currently we have no knowledge about how soil management will affect such biological and physical interactions. The results of this research will tell us how the soil microbial community affects the performance of the soil surface, and provide the fundamental knowledge necessary for designing ways to manage soil systems more effectively and sustainably.