• Trees reduce their carbon (C) allocation to roots and mycorrhizal fungi in response to high nitrogen (N) additions, which should reduce the N retention capacity of forests. The time needed for recovery of mycorrhizas after termination of N loading remains unknown. • Here, we report the long‐term impact of N loading and the recovery of ectomycorrhiza after high N loading on a Pinus sylvestris forest. We analysed the N% and abundance of the stable isotope ¹⁵N in tree needles and soil, soil microbial fatty acid biomarkers and fungal DNA. • Needles in N‐loaded plots became enriched in ¹⁵N, reflecting decreased N retention by mycorrhizal fungi and isotopic discrimination against ¹⁵N during loss of N. Meanwhile, needles in N‐limited (control) plots became depleted in ¹⁵N, reflecting high retention of ¹⁵N by mycorrhizal fungi. N loading was terminated after 20 yr. The δ¹⁵N and N% of the needles decreased 6 yr after N loading had been terminated, and approached values in control plots after 15 yr. This decrease, and the larger contributions compared with N‐loaded plots of a fungal fatty acid biomarker and ectomycorrhizal sequences, suggest recovery of ectomycorrhiza. • High N loading rapidly decreased the functional role of ectomycorrhiza in the forest N cycle, but significant recovery occurred within 6-15 yr after termination of N loading.