SurfinSoil: Surfaces in soil predict bacterial functioning

Soils are important reservoirs and sources of atmospheric carbon. Within the soil, microorganisms act as engines that drive the transformation of this carbon. Bacteria, in particularfound at concentrations of about one billion cells per gram of soilplay a vital role. They are heavily involved in both the breakdown of organic carbon and its storage, as well as in its potential release as CO2. The activity of these microorganisms is, therefore, of great importance for global nutrient cycles, especially in light of climate change and the resulting increase in atmospheric CO2 concentrations. To better understand bacterial functioning in soil, it is necessary to consider the spatial complexity of their habitat. Soil is a porous system, with the solid components mainly consisting of minerals such as sand, silt, and clay. The space between these mineral particles is called soil pores, whose surfaces are colonized by bacteria. The amount of pore surface area depends largely on the mineral composition of a soil: soils rich in clay can have up to a thousand times more surface area than sandy soils. However, many of these pores are smaller than a typical bacterium, and thus not accessible. In scientific literature, a greater pore surface area has so far been associated with increased potential for carbon storage. This overlooks the fact that bacteria, being relatively large compared to some of these pores, can only colonize a portion of the total pore surface. Consequently, a universal relationship between soil mineral composition and microbial processessuch as the release of CO2has not yet been established. In this project, we are, for the first time, focusing on measuring the pore surfaces in various soils that are actually accessible to bacteria. Our multidisciplinary approach combines soil physics with microbial ecology. By using non-invasive microtomography, we can reconstruct the pore space within soil samples, including the measurement of surfaces available for bacterial colonization. By subsequently determining the number of bacterial cells, this method enables a data-driven assessment of bacterial population densities in diverse soils. At the same time, the samples undergo a series of measurements to assess functional parameters of bacterial activity. Together, these data will help us identify relationships between pore surface area, bacterial population density, and microbial functions. Successfully uncovering such patterns could make it possible to predict specific bacterial functions such as carbon transformationwith just a few soil physical and microbiological measurements.