The aim of this study was to identify the parameters that affect the nitrogen (N) isotope ratio (δ¹⁵N) in soils of temperate and boreal forests. We measured the δ¹⁵N in 30 soil profiles of temperate and boreal forests in Sweden and analyzed the relationships between δ¹⁵N in the soils and soil chemical properties as well as site characteristics. In addition, we conducted a meta-analyses of δ¹⁵N in the organic layer of European forests. We identified two types of δ¹⁵N patterns; in type D soils, the δ¹⁵N in the mineral soil decreases with depth, whereas in type C soil, the δ¹⁵N in the soil profile is almost constant. Type D soils had a significantly higher δ¹⁵N in the organic layer and upper mineral soil than type C soils, which is likely due to N isotope fractionation by ectomycorrhizal fungi in the topsoil. Type D soils were found in boreal forests, but not in temperate forests. They had a significantly lower atmospheric N deposition rate than type C soils, by a factor of 2.3, and a significantly higher phosphorus (P) concentration of the organic layer than type C soils, by a factor of 1.5. We also found that the δ¹⁵N was negatively correlated with the N:P ratio of the organic layer (R² = 0.21, p < 0.001). Across Europe, the δ¹⁵N of the organic layer was positively correlated with latitude (R² = 0.58, p < 0.001), and negatively with mean annual temperature (R² = 0.52, p < 0.001) and atmospheric N deposition (R² = 0.42, p < 0.001). In conclusion, our results show that the δ¹⁵N of the organic layer and microbial N (re-)cycling in forest soils is positively related with latitude and the P concentration of the organic layer.