C fractionation in transformations at the interface between roots, microorganisms, soil organic matter and soil respiration

Introduction Natural variations of the C/C ratio have been frequently used over the last three decades to trace C sources and fluxes between plants, microorganisms, and soil. Most of these studies have used the natural C labelling approach, i.e. natural δC variation after C3 – C4 vegetation changes. In this mini-review, we focus on C fractionation in processes at the interface between roots, microorganisms, and soil: root respiration, microbial respiration, formation of dissolved organic carbon by root exudation, as well as microbial uptake and utilization of soil organic matter (SOM).