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。微生物过程尚未被讨论为土壤侵蚀的重要控制因素，尽管它们通过产生胞外聚合物（EPS）与团聚体稳定性直接相关。目前还不清楚是否由植被影响的细菌群落的组成影响EPS原位生产。EPS的数量和组成的变化及其对土壤团聚体稳定性的影响，从而对土壤水蚀在很大程度上是未知的。因此，本提案的主要目标是研究植被之间的复杂相互作用，土壤细菌群落的组成和产生EPS的能力，以及这些EPS对形成的团聚体的稳定性和随后对土壤易受侵蚀性的影响。在我们的项目中，我们将跨越不同的时间和空间尺度，并提高我们对生物调节侵蚀和沉积物路由取决于气候的知识。我们将使用两个梯度，沿着西班牙南部（阿尔梅里亚省）的降水梯度和每个研究区域内的植被覆盖梯度的三个研究区域。该项目将从探索性实地调查开始，以研究植被，细菌群落组成，EPS的数量和性质之间的关系，以及这些关系如何影响骨料稳定性。然后，联合温室和根箱实验将被用来详细研究如何EPS形成的土壤细菌影响团聚体的稳定性，在有或没有植物根系。根盒实验将在细菌EPS生产的空间方面提供深刻的见解，以及它如何与根和聚集相关。田间降雨模拟试验将最终证明EPS控制的团聚体稳定性的变化是否会导致土壤水蚀的原位变化。在我们的项目中，我们将建立新的方法来提取和表征EPS从土壤中，并确定其空间分布模式。在所有的实验方法中，我们将使用相同的土壤样品，并将联合收割机先进的方法结合起来，这些方法涵盖了从分子微生物生态学（例如，16 S rRNA扩增子测序、定量PCR、PCR-Southern印迹杂交）、显微镜（例如，CLSM、CARD-FISH、gold-FISH、ESEM）、土壤科学（例如，聚集体大小分级、聚集体稳定性）、光谱学（荧光、热解GC/MS、高分辨率MS）和地貌学（降雨模拟）。在这里，我们提出了一个创新的和跨学科的方法，使前所未有的见解如何通过水的土壤侵蚀是由细菌群落通过其生产的EPS及其对聚集体稳定性的影响控制。

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.