Organic substances in the soil are very heterogeneous and include low and high molecular weight compounds, and may be derived from plant and microbial residues. Besides contribution to soil organic matter (SOM) formation, living microorganisms regulate C and nutrient cycles by recycling processes. Detailed analyses of SOM transformation can highlight the role of selective preservation mechanisms, for example, and how these are modified and influenced by biological, physical and chemical interactions. In order to link processes of SOM formation with the pools, the broad range of approaches is used, including an application of various isotopes 13C/14C, 15N, 18O, 33P and analysis of plant and microbial biomarkers comprising both structural and chemical aspects related to SOM turnover. The specific attention is dedicated to the low molecular weight organic substances (LMWOS), which serve as a fuel for microorganisms, regulates their activity, composition, the transition from dormant to active stages and transformation of SOM (e.g. priming effect).
Thus, this session invites contributions, especially from early-career students, to i) the fate and turnover of organic substances in soil: from uptake and utilization by microorganisms to stabilization in SOM, ii) functions of LMWOS for priming of SOM decomposition, regulation of nutrient availability and rock weathering, iii) microbial recycling of elements (C, N, and P) from fresh or aged organic material. Analytical approaches comprising structural and chemical aspects related to SOM, such as potential biomarkers, isotopes, and their combinations are highly desirable. We also encourage contributors to present and discuss analytical challenges that remain due to both environmental and analytical uncertainty.