Contribution of belowground biomass carbon to the stable soil organic matter pools

Crop residues are the primary carbon (C) source of soil organic carbon (SOC). Different plant parts could have specific behaviors in soil partially due to not only contrasting biochemical characteristics, but also the source-dependent interactions with soil. The residence time in soil of belowground biomass has already been proven to be longer than that of aboveground residues (i.e. shoots) in the field. In this project, we aim to support the scarce existing evidence of the relative stability of root-derived C in soil and to investigate the potential mechanisms for its stability. In addition, we aim to better understand how well root biomass could be predict based on the more commonly quantified aboveground biomass and how variable this relation between both plant compartments is. We found that the relative stability of below- and above-ground biomass measured over a decadal period differs by a factor of 3.5. This implies that management oriented at storing SOC needs to be root-oriented and this knowledge could further help to improve the prediction of SOC dynamic by biogeochemical modeling. Root biomass is mostly predicted based on aboveground yield by fixed R/S ratios, often leading to over- or underestimation under various soil conditions. Therefore, fast and reliable quantification of root biomass remains another big challenge to improve simulations of dynamics of SOC.