Authors:
Jeremy Detrey | INRAE, UMR Eco&Sols, Montpellier, France | France
Dr. Isabelle Bertrand | INRAE, UMR Eco&Sols, Montpellier, France | France
Dr. Jim Rasmussen | Aarhus University, Department of Agroecology | Denmark
Dr. Gabin Piton | INRAE, UMR Eco&Sols, Montpellier, France | France
Increasing soil carbon (C) sequestration in diversified agroecosystem was identified as a way to achieve climate neutrality. Since root represents a major source of C soil organic carbon (SOC), quantifying the root-C input into SOC is of tremendous importance. Root turnover and rhizodeposition are the two dominant pathways of root-C inputs. While the importance of these processes is well established, there is a real lack of quantification under field conditions, partly due to methodological difficulties. Further, in diversified agroecosystems such as alley cropping agroforestry, the understory vegetation strip on the tree row is mainly composed of perennial herbaceous vegetation while inter-row are made of annual crops. This lead to contrasting rooting systems and may impact the net rhizodeposition in surface and in deeper soil horizons, that might be enriched by deep roots of perennials. Indeed, most of the available data on rhizodeposition concerns topsoil, while subsoil (> 30 cm depth) is identified to have longer C residual time. In this study, performed within the EJPSoil MIXROOT-C project we carried out a 13C labelling experiment in a Mediterranean agroforestry system to quantify the net rhizodeposition (gross rhizodeposition – loss by mineralization) of herbaceous plants in top- and subsoil (0-100 cm). Plants were labelled twice a week with 13CO2 pulse during the full growing period (7 weeks in Spring 2023). Plant and soil were sampled at peak biomass with roots and soils collected up to 1m depth. Then, 13C excess in shoot, root and soil was used to calculate the net rhizodeposition and the amount of rhizodeposited-C stabilized as SOC at 4 soil depths (0-20, 20-30, 30-50, and 50-100 cm) for barley (at two distances from the tree, in the inter-row) and grass mixture (below the trees). Overall, in this study we provide original data that will help to assess the potential of agroecosystem diversification to foster SOC in top and subsoils through rhizodeposition.