Mahmud M. auteur aut IRD Bertrand I. auteur aut IRD Ngao J. auteur aut IRD Martin-Blangy S. auteur aut IRD Bazot S. auteur aut IRD Delpierre N. auteur aut IRD Leadley P. auteur aut IRD Vincent G. auteur aut IRD Marsden C. auteur aut IRD Dugué Rémi auteur aut IRD Morfin A. auteur aut IRD Forest M. auteur aut IRD Marmagne A. auteur aut IRD Barthes L. auteur aut IRD text journalArticle eng text/pdf reformatted digital access A 2-years assessment of nitrogen (N) stocks, tree N safety nets (from a 15N labeling experiment), and biological N fixation was conducted in a Mediterranean agroforestry system in southern France. The study aimed to quantify N retention in agroforestry. The study area is characterized by a skeletic rhodic luvisol soil, a mean annual temperature of 15.5 degrees C, and an average annual precipitation of 556 mm. N and 15N were quantified across all system components, which are N-fixing black locust trees, crops, weed plants, understory vegetation strips (UVS), rhizospheric soil, and soil microbial biomass. A split-plot experimental design was used, with agroforestry (AF) and monoculture (MC) plots. 15N labeling was applied to track N fluxes and determine tree nutrient absorption over time. We hypothesized that tree root growth and nutrient leaching would enhance the safety-net effect, improving N retention. Results showed that crops in AF had lower N stocks (13-30% less than MC), but tree and UVS contributions compensated for the deficit, leading to a 62% increase in total plot-level N stock in 2022. The Relative Nitrogen Content was 0.97 in 2021 and 1.63 in 2022. While no 15N was detected in trees in the first year (70 days after labeling), 2% of applied 15N was recovered in trees 14 months post-labeling. % of N derived from atmospheric N2 (%Ndfa) ranged from 52 to 68%, with trees fixing 14-18 kg N ha-1. We confirmed that agroforestry enhances N retention, but further research is needed to quantify leaching and gaseous losses of nitrogen. specialized Black locust Safety net N-15 %Ndfa Biological fixation Microbial biomass FRANCE ZONE MEDITERRANEENNE 076 084 082 99 7 182 [16 p.] 2025 0167-4366 https://www.documentation.ird.fr/hor/fdi:010094918 10.1007/s10457-025-01264-y 0167-4366 [F B010094918] https://www.documentation.ird.fr/hor/fdi:010094918 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2025-10/010094918.pdf IRD - Base Horizon / Pleins textes 2025-10-29 2026-06-12 fdi:010094918 fre