Nitrogen cycling studies in unpolluted forests can provide valuable information on kinetics and pathways of soil N transformations, and how N deposition might affect the N cycle. In a laboratory experiment, gross N consumption and production rates were determined in the mineral soil layer of an old-growth evergreen unpolluted forest in southern Chile, by a combination of ¹⁵N enrichment experiments and a dynamic ¹⁵N tracing model. Tracing models are powerful tools, allowing quantification of the extent of simultaneous N transforming fluxes. They provide significant surplus values compared to classical analytical solutions. The possibility to account for recycled N material and different kinetic parameter options are main advantages. The ¹⁵N tracing model included six different N pools (labile organic matter (Nmom), recalcitrant organic matter (NrSOM), NH₄⁺, NO₃^-, and two dissolved organic N pools (NH₄⁺-DON and NO₃^--DON)), and ten important gross transformation fluxes. The model was able to simulate the obtained data set, including three different labeling treatments of NH₄⁺ and NO₃^-. Results indicated a fast turnover of the NH₄⁺ and DON pool, contrary to slow N dynamics related to the NO₃^- pool. Neither biotic nor abiotic NO₃^- immobilization reactions towards insoluble soil organic matter (SOM) were observed in this forest. However, low gross nitrification fluxes act as a mechanism preventing accumulation of NO₃^- in the ecosystem, and retaining N within the soil profile. Immobilization processes having NH₄⁺ as substrate include fluxes towards Nmom, NrSOM and DON pools. The DON immobilization was found to be most important flux in this soil, indicating the potential of NH₄⁺ as substrate for DON formation. DON can be adsorbed at insoluble organic matter, but high DON leaching fluxes observed in this forest indicate likewise the potential of DON losses, originating from the NH₄⁺ pool. N losses in gaseous form were negligible in this forest as NH₄⁺ was shown to be the end product of NO₃^- reduction via dissimilatory nitrate reduction (DNRA). It was found that this forest ecosystem managed low inorganic N inputs with a high efficiency in order to avoid N losses from the ecosystem. However, the absence of a real NO₃^- immobilization mechanism indicates a potential risk for NO₃^- leaching losses, eventually under increased future N deposition scenarios, influencing forest vitality and water quality of the surrounding watersheds.