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Soil organic carbon (SOC) pools in forest floors and mineral soil to a depth of 100 cm were determined in 234 well‐drained Nordic forest soils from latitude 55–68?‚??°‐N, and longitude 6–28?‚??°‐E. The data were compiled in a database of Nordic forest soils, from literature, and sources of validated data the authors had access to. The SOC pool increased with both mean annual temperature (MAT) and mean annual precipitation (MAP), and the increase with MAT was more pronounced for coarse‐textured soils than for medium‐textured soils. Soil organic carbon in fine‐textured soils was not correlated with MAT and MAP. Differences between texture classes were mainly due to different carbon stores in the upper 40 cm of the mineral soil and in the forest floor. The emphasis on well‐drained soils eliminated the impact of hampered decomposition in hydromorphic soils. Large carbon accumulation in such soils probably explains the negative relationship between SOC and temperature reported in other studies. The increase in SOC with temperature and precipitation is interpreted as an indirect effect of higher net primary production.

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Summary• 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 15 N in tree needles and soil, soil microbial fatty acid biomarkers and fungal DNA.• Needles in N-loaded plots became enriched in 15 N, reflecting decreased N retention by mycorrhizal fungi and isotopic discrimination against 15 N during loss of N.Meanwhile, needles in N-limited (control) plots became depleted in 15 N, reflecting high retention of 15 N by mycorrhizal fungi. N loading was terminated after 20 yr.The d 15 N 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.

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