Extracellular polymeric substances and aggregate stability - how microorganisms affect soil erosion by water

土壤侵蚀决定了许多景观的形状和表面，土壤团聚体的稳定性被认为是调节土壤侵蚀的关键因素。微生物过程作为土壤侵蚀的重要控制因素尚未被讨论，尽管它们应该通过生产细胞外聚合物（EPS）与团聚体稳定性直接相关。目前尚不清楚受植被影响的细菌群落组成是否会影响原位产生的EPS。EPS的数量和组成的变化及其对土壤团聚体稳定性的影响，从而对水土流失的影响在很大程度上是未知的。因此，本研究的主要目的是研究植被、土壤细菌群落组成和产生EPS的能力之间的复杂相互作用，以及这些EPS对形成的团聚体稳定性和土壤侵蚀敏感性的影响。在我们的项目中，我们将跨越不同的时间和空间尺度，增强我们对气候对侵蚀和沉积物路径的生物调节的了解。我们将使用两个梯度，沿着西班牙南部（Almería省）的降水梯度使用三个研究区域，并在每个研究区域内使用植被覆盖梯度。该项目将从探索性的实地调查开始，研究植被、细菌群落组成、EPS数量和性质之间的关系，以及这些关系如何影响聚集体的稳定性。然后，通过温室和根箱联合试验，详细研究在植物根系存在或不存在的情况下，土壤细菌形成的EPS对团聚体稳定性的影响。根箱实验将在细菌EPS生产的空间方面提供深刻的见解，以及它与根和聚集的关系。田间降雨模拟试验将最终证明EPS控制的团聚体稳定性变化是否会导致水土流失的原位变化。在我们的项目中，我们将建立从土壤中提取和表征EPS并确定其空间分布模式的新方法。在所有的实验方法中，我们将使用相同的土壤样品，并结合分子微生物生态学（例如，16S rRNA扩增子测序，定量PCR， PCR- southern杂交），显微镜学（例如，CLSM, CARD-FISH, gold-FISH， ESEM），土壤科学（例如，团聚体大小分级，团聚体稳定性），光谱学（荧光，热解GC/MS，高分辨率MS）和地貌学（降雨模拟）的先进方法。在这里，我们提出了一种创新的跨学科方法，使我们能够前所未有地了解细菌群落如何通过产生EPS及其对骨料稳定性的影响来控制土壤侵蚀。

Soil erosion determines the shape and surface of many landscapes and the stability of soil aggregates is considered to be a crucial factor regulating soil erosion. Microbial processes have not been discussed as important controls of soil erosion although they should directly be related to aggregate stability by the production of extracellular polymeric substances (EPS). It is unknown whether the composition of the bacterial community as influenced by vegetation affects EPS produced in situ. Changes in amount and composition of EPS and their effects on the stability of soil aggregates and thus on soil erosion by water are largely unknown. Therefore, the main objective of this proposal is to study the complex interactions between vegetation, the composition and capability of the soil bacterial community to produce EPS, and the effects of these EPS on the stability of formed aggregates and subsequently on soils susceptibility to erosion. In our project we will bridge different temporal and spatial scales and enhance our knowledge about biotic modulation of erosion and sediment routing depending on climate. We will use two gradients, three study areas along a precipitation gradient in Southern Spain (Almería Province) and a gradient in vegetation coverage within each study area. The project will start with an explorative field survey to study relationships between vegetation, bacterial community composition, and amount and properties of EPS and how aggregate stability is affected by these relationships. Then, joint greenhouse and rhizobox experiments will be used to study in detail how EPS formed by soil bacteria influence aggregate stability in presence or absence of plant roots. The rhizobox experiment will deliver deep insights in spatial aspects of bacterial EPS production and how it is related to roots and aggregation. Rainfall simulation experiments in the field will be the ultimate proof whether changes in aggregate stability controlled by EPS will be responsible for in situ changes in soil erosion by water. In our project we will establish novel methods to extract and characterize EPS from soils and to determine their spatial distribution patterns. In all experimental approaches we will use the same soil samples and combine advanced methods spanning a broad range from molecular microbial ecology (e.g., 16S rRNA amplicon sequencing, quantitative PCR, PCR-Southern blot hybridization), microscopy (e.g., CLSM, CARD-FISH, gold-FISH, ESEM), soil science (e.g., aggregate size fractionation, stability of aggregates), spectroscopy (fluorescence, pyrolysis GC/MS, high resolution MS) and geomorphology (rainfall simulations). Here we present an innovative and interdisciplinary approach enabling unprecedented insights how soil erosion by water is controlled by bacterial communities via their production of EPS and their effects on aggregate stability.