Research Group Soil Chemistry

The reactivity of soils is based on the formation of dynamic and hierarchically organised biogeochemical interfaces, built up from mineral and organic solid phases as well as microorganisms. Many soil-forming processes at these biogeochemical interfaces, e.g. the release of nutrients through mineral weathering, the stabilisation of soil organic matter and the immobilisation of pollutants determine the soil functions and services that are so important for our society, such as plant production and safeguarding biodiversity, carbon storage and ensuring clean drinking water.

Depending on the environmental conditions, soils can be either a carbon sink or source, thus have a massive impact on the global climate. We therefore want to better understand the transformation and stabilisation processes of soil organic matter as a function of climate and land use in order to manage the carbon and nutrient balance of soils sustainably. In our research projects, we mostly work on ecosystem gradients, in which we analyse the relationships between the functional diversity of biological communities, the genesis of pedogenic minerals and the turnover of soil organic matter. For this purpose, we travel all over the world, e.g. in permafrost regions, the humid tropics or in dry steppes. Our field experiments are accompanied by detailed micro- and mesocosm experiments in the laboratory, in which environmental variables are manipulated in a controlled manner. Methodologically, we use a large repertoire of (micro)spectroscopic, chemolytic, isotope analytical and molecular biological methods.

Soils emerge from the activity of life, as soil development is a constant dialogue between life and the lifeless. We explore this dialogue across multiple scales.  The interplay of climate and ecosystem competition for nutrients can lead plants with their symbionts and associated microorganisms to change the soil massively and surprisingly quickly. They do this, for example, through biogenic weathering and new formation of secondary soil minerals such as clay minerals and aluminium and iron oxides, and under anoxic conditions also Fe(II) minerals. These altered or newly formed mineral phases play an important role in numerous soil functions, such as the binding of organic matter. In order to better understand these processes, we are studying ecosystems whose general conditions are special, such as Amazonia, Antarctica, the Tibetan highlands, the Atacama, rice soils of China and tidal flat soils of the Elbe. This allows us to recognise the influence of, for example, temperature, drought, functional biodiversity, precipitation distribution, soil age or mineralogical composition on the ongoing biogenic soil evolution. This knowledge also allows us to improve the use and protection of soils.

Basic research in various regions of the world, provides the basis for a deeper systems understanding of the complex interactions between biology and mineral phases in the soil. Only in this way it is possible to use ecosystem services in a targeted manner and to develop concepts for sustainable agro-ecosystems from them. On agricultural land, the complexity of the processes taking place in the soil is reduced. But it is precisely this complexity that generates soil fertility on natural sites without producing nutrient surpluses. We are working to decipher the diversity of natural processes taking place in the soil and to map them into agricultural practices. For example, our research projects investigate how increasing plant diversity in agricultural soils affects soil life and biogeochemical cycling, and how organic amendments (e.g. compost) can be produced and applied sustainably.

The aggregation behaviour of soil colloids and particles is of crucial importance for many processes and functions of soils. We are investigating the extent to which dissolved organic matter and flux conditions control the stability and mobility of mineral colloids. This is important for the mobility of pollutants in soils, such as lead and microplastics. In addition, we study how different biotic and abiotic processes contribute to the formation of soil microaggregates (20-250 µm) via cementing substances and to what extent this contributes, for example, to carbon storage in soils. We investigate conditions of stable aggregation by analysing the composition and charge ratios of various fine particles occurring in the soil towards their outermost surface exposed to the soil solution. The findings obtained are evaluated in model experiments on aggregation.