Soil Pores affecting Carbon Mineralisation at nanoscales (SoilPACMAN) - Determining how soil organic carbon dynamics are locally controlled by the organo-mineral microenvironment of microbes in the pore space – SoilPACMAN

The co-location of organic matter (OM) and microbial decomposers is fundamental for the dynamics and the persistence of organic carbon in soils. Various studies have demonstrated that the spatial distribution of OM and its accessibility to microbial decomposers across different pore sizes have profound impacts on the turnover of carbon in soil. An integration of the effects that the biogeochemically heterogeneous organo-mineral microenvironment can have on the activity of the microbial inhabitants is, however, lacking. Here we propose a collaborative Franco-German project that brings together complementary expertise on physicochemical carbon storage mechanisms and soil microbial carbon fluxes. A novel approach using porous ceramics coated with soil minerals, which will result in stable and known physicochemical properties at the microenvironmental scale, will be used to disentangle dynamic microbial interactions at biologically-relevant scales. This approach will allow us to test the influence of reactive mineral surfaces and the distribution of 13C-labelled organic matter in specific pore size classes (< 1, 5-10 vs. 20-30 µm) on microbial carbon dynamics during laboratory incubations. Our correlative spectromicroscopic workflow, which includes NanoSIMS, will enable the biogeochemical characterization of local microenvironments with potentially contrasting effects on carbon storage. Incubation experiments will also be set up to analyze carbon dynamics under the climate-change related disturbances of increased temperature and dried and re-wetted porous systems. We expect to decipher how such disturbances affect the local interplay between the organo-mineral microenvironment and microbial activity. The acquired data will be integrated into a holistic model description that enables the evaluation of the importance of different microenvironmental features on locally different organic carbon dynamics. The modelling tool will help to better understand and predict effects of the spatial distribution of microbes and their local interactions with heterogeneous properties of their organo-mineral microenvironment. Our novel microcosm approach enables unravelling the underlying local mechanisms of microbial soil carbon in a complex pore space. This will help to extend our understanding based on the physical and biogeochemical interplay of soil microenvironments where local interactions and a distinct spatial architecture controls the concerted activities of microbes and the turnover of soil organic carbon at the biologically-relevant scale.