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Quantification; spatial distribution and persistence of root-derived carbon for 12 crop species
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DOI：10.5194/bg-23-4343-2026.png)
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Abstract
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Abstract. Organic carbon derived from roots is a major input fuelling soil organic carbon stocks; especially in agricultural systems; where aboveground biomass might be harvested. However; root sampling for carbon monitoring excludes net rhizodeposition; i.e.; the organic compounds released by the roots that have not been rapidly mineralised; and some of the finest root debris; because this fraction of root-derived carbon cannot be directly quantified in the field. To compensate for this shortfall; we set up a two-month experiment with multi-pulse 13C-CO2 labelling of 12 crops to quantify these carbon pools at harvest; operationally grouped under the term SOCnew. We also investigated the spatial distribution of belowground carbon inputs within the soil profile. Lastly; in order to follow the fate of this carbon after the plant death; we performed a 524 d litterbag incubation in the field using the labelled material. We found that SOCnew accounted for 27 % of belowground carbon inputs at harvest. It was not correlated to carbon amounts of the shoots; but was positively correlated to root carbon (R2=0.14). The vertical distribution of SOCnew tended to follow the one of roots. The majority of SOCnew was recovered in the bulk soil; rather than solely adhering to the roots; which suggests that its release may influence SOC cycling across a large proportion of the soil volume above the rooting depth. We showed that SOCnew had a greater persistence time in the soils than roots throughout the 524 d observation period. However; these findings were marked by high variability because the small quantities of carbon involved make it difficult to assess persistence by isotopic difference. These results suggest that net rhizodeposition and fine root debris should be taken into account in organic carbon management of soils as it refines our estimation of belowground inputs. However; their low predictability; due to the diversity of products and processes; is still a barrier.
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