Plant rhizodeposition: A key factor for soil organic matter formation in stable fractions

Soil organic carbon formation remains poorly understood despite its importance for human livelihoods. Uncertainties remain for the relative contributions of aboveground, root, and rhizodeposition inputs to particulate (POC) and mineral-associated (MAOC) organic carbon fractions. Combining a novel framework with isotope tracer studies, we quantified POC and MAOC formation efficiencies (% of C-inputs incorporated into each fraction). We found that rhizodeposition inputs have the highest MAOC formation efficiency (46%) as compared to roots (9%) or aboveground inputs (7%). In addition, rhizodeposition unexpectedly reduced POC formation, likely because it increased decomposition rates of new POC. Conversely, root biomass inputs have the highest POC formation efficiency (19%). Therefore, rhizodeposition and roots appear to play opposite but complementary roles for building MAOC and POC fractions.

Automated summary

The formation of soil organic carbon is poorly understood, with uncertainties remaining for the contributions of different inputs to the particulate and mineral-associated organic carbon fractions. Rhizodeposition has the highest efficiency in forming MAOC, while root biomass inputs have the highest efficiency in forming POC. Rhizodeposition and roots play opposite but complementary roles in building MAOC and POC fractions.