Root distribution and traits in a young alley-cropping system: impacts on soil carbon storage, nutrient dynamics and microbial activity

Abstract Purpose In alley-cropping systems, the root distributions and traits of the annual and perennial vegetation are poorly known, although they are recognized as factors fostering soil carbon (C) stocks through annual root C inputs and by impacts on microbial activity. This study aimed to evaluate the potential contribution of roots from the understory vegetation strip (UVS) and the crop to top- and subsoil C stocks (0-100 cm) in a 3-year-old alley-cropping system. Methods Root biomass, chemical composition, functional traits and anatomical structure were assessed in parallel to a characterization of soil physico-chemical and microbiological properties, including enzymatic activity, at different depths and locations perpendicular to the tree line, reflecting the effect of the distance to the tree. Results The root biomass and traits were heterogeneous in the young alley-cropping system due to the presence of different plant species and the heterogeneity of the soil mineral N content according to the location perpendicular to the tree line. The soil microbiological properties and organic C stocks did not vary horizontally at this stage of agroforestry, but the tight link between root stoichiometry and microbial extracellular enzymatic activities suggested a differentiation of the soil properties in the following years. Conclusion Altogether, our results suggested that increasing the root biomass in topsoil in agroforestry systems can positively contribute to increasing soil organic C stocks, but in deeper soil layers, an increase in litter inputs with high C:N could accentuate microbial N limitations and limit soil C storage.