Microorganisms and the turnover of soil aggregates: The importance of extracellular polymeric substances

土壤团聚体对固碳、植物生长和土壤肥力至关重要。微生物过程已被认为是聚集体周转（形成，稳定性和破坏）的重要控制。然而，微生物如何促进这些过程仍然是一个有争议的问题。决定聚集体周转率的一个关键机制可能是胞外聚合物（EPS）作为微生物胶的分泌，但EPS的量和组成对宏观聚集的作用在很大程度上是未知的。此外，重要的聚集因素之间的相互依赖性，如细颗粒（粘土）的数量，有机物和微生物的可分解性（数量和组成，以及EPS的排泄）仍然知之甚少。因此，本建议的主要目标是研究这些因素之间的复杂相互作用及其在总周转量中的作用。总体目标是评估和确定的机制，定义的时间模式的大团聚体营业额方面的作用，微生物。因此，该项目的重点是EPS对宏观骨料形成和稳定的作用。该项目的基础是培养实验，该实验将在粘土含量和基质分解性的梯度上进行，作为微生物活性的主要驱动因素。我们假设，微生物活性的增加，诱导的有机底物的输入，将刺激EPS的生产，从而形成和稳定的聚集体。此外，我们预期EPS-蛋白质将比EPS-多糖更增加聚集体稳定性。将应用聚集体分离和稳定性试验的组合。结果将检查相对于获得的微生物参数（CO2呼吸，微生物生物量，磷脂脂肪酸，EPS的量和组成），解开的机制和因素控制大团聚体营业额受土壤微生物的影响。我们将直接评估EPS-蛋白质或EPS-多糖是否对大聚集体稳定性贡献更大。将获得水稳定的大骨料，并测量其中EPS的量和组成。在这方面，高分辨率质谱将提供一个非常详细的视图到EPS的分子组成。预计该分析将提供EPS对大团聚体稳定性的作用的结论性结果。在这里，我们提出了一个创新的和跨学科的方法来解开大骨料营业额是如何控制的微生物，特别是通过检查他们的作用，在生产和组成的EPS。该项目将提供一个更好的理解的基本过程的大团聚体在土壤中的周转，这是必要的实施更好的土壤管理做法，以改善土壤结构，减少对表土侵蚀的敏感性，并提高碳固存。

Soil aggregation is critical for carbon sequestration, plant growth, and soil fertility. Microbial processes have been recognised as an important control of aggregate turnover (formation, stability, and destruction). However, how microorganisms contribute to these processes is still a matter of debate. One crucial mechanism determining aggregate turnover may be the excretion of extracellular polymeric substances (EPS) as microbial glue, but the role of the amount and composition of EPS on macroaggregation is largely unknown. Moreover, interdependencies between important aggregation factors like the amount of fine-sized particles (clay), the decomposability of organic matter and microorganisms (amount and composition, as well as the excretion of EPS) are still poorly understood. Thus, the main objective of this proposal is to study the complex interactions between these factors and their role in aggregate turnover. The overarching goal is to evaluate and identify the mechanisms defining the temporal patterns of macroaggregate turnover with respect to the role of microorganisms. Thereby, the project focuses on the role of EPS for macroaggregate formation and stabilisation. The basis of this project is an incubation experiment which will be conducted across a gradient of clay content and substrate decomposability as main drivers of the microbial activity. We hypothesise that an increase in microbial activity, induced by the input of organic substrates, will stimulate EPS production and therefore the formation and stability of aggregates. Furthermore, we expect that EPS-proteins will increase aggregate stability more than EPS-polysaccharides. A combination of aggregate separation and stability tests will be applied. The results will be examined with respect to the obtained microbial parameters (CO2 respiration, microbial biomass, phospholipid fatty acid, amount and composition of EPS), to disentangle the mechanisms and factors controlling macroaggregate turnover affected by soil microorganisms. We will directly evaluate if EPS-proteins or EPS-polysaccharides contribute more to macroaggregate stability. Water-stable macroaggregates will be obtained, and the amount and composition of EPS will be measured therein. In this regard, high resolution mass spectrometry will offer a very detailed view into the molecular composition of EPS. This analysis is expected to provide conclusive results on the role of EPS on the stability of macroaggregates. Here we present an innovative and interdisciplinary approach to disentangling how macroaggregate turnover is controlled by microorganisms, in particular by examining their role in the production and composition of EPS. This project will provide an improved understanding of the underlying processes of macroaggregate turnover in soils, which is necessary for the implementation of better soil management practices, to improve soil structure, reduce susceptibility to topsoil erosion, and enhance C sequestration.