A novel approach to study composition of in situ produced root-derived dissolved organic matter

Carbon (C) compounds released from plant roots comprise a significant and reactive fraction of belowground C pools. These root-derived compounds modify rhizosphere soil and play a vital role in the mobility of nutrients and contaminants within ecosystems. Due to their low concentration, fast turnover, and limited spatial distribution throughout the soil, root-derived compounds are difficult to study. This study combined a ¹³C pulse-chase technique and 1D and 2D nuclear magnetic resonance (NMR) spectroscopy techniques to analyze root-derived compounds produced in real soil. The pulsed samples displayed distinct enrichment in aliphatic and carbohydrate-type compounds indicating that pulse-chase approaches are a viable technique for isolating root-derived from background DOM. However, multiple NMR techniques may be necessary to develop a full profile of root-derived DOM. This is the first use of combined pulse-chase-NMR methodologies to analyze in situ produced root-derived DOM. Such a combination is applicable to various experimental designs and/or environmental scenarios, and can provide valuable information for future rhizosphere science. •Soil solution contained 1.8 atom% ¹³C 4h after a 3-h99 atom% ¹³C-CO₂ pulse.•Root-derived DOM contained aliphatics and carbohydrates as measured by HMQC NMR.•Absence of carboxylic acids is likely due to resolvable analytical limitations.•Pulse-chase with NMR is useful to identify root-derived DOM in situ.