A 15N pulse chase study was carried out in a south Chilean Nothofagus betuloides forest soil, characterized by low N inputs and absence of human disturbance. We applied 15N pool dilution, combined with 15N pulse tracing as a complementary approach to gain insight in the kinetics, short- and long-term fate of inorganic N additions. High gross mineralization rates (21.0 ± 10.2 mg N kg-1) assure a constant nutrient availability for vegetation and microbial community structures. Heterotrophic nitrification appeared to be, almost exclusively, the dominant gross NO3- production (2.3 ± 0.6 mg N kg-1) pathway. Nitrate consumption processes, such as dissimilatory nitrate reduction to ammonium (DNRA) and fast immobilization to soil organic matter (SOM) maintained standing NO3- pool sizes low and assure a tight N cycling. The short-term fate of the 15NH4+ was indicated to be mainly soil organic matter (50%) followed by NH4+ (42%), microbial biomass (13%) and roots (6%). The small transfer of 15NH4+ to NO3- can be explained by the limited occurrence of autotrophic nitrification in this Andisol. In the short-term, 15N-NO3- was relocated to soil organic matter (62%), soluble organic N (21%), NH4+ (6%) and roots (6%). Completer disappearance of the 15N-NO3- 1 day after addition, indicated a high turnover of NO3-. One year after 15N addition, 84% and 69% (for 15N-NH4+ and 15N-NO3-, respectively) of the label was recovered in the 0-10 cm soil layer, mainly in the SOM and root N pool. Leaching losses of 15N pulses could only be found shortly after 15N addition, indicating that continuous dissolved organic nitrogen (DON) losses as a result of dissolved inorganic nitrogen (DIN) turnover do not seem plausible. The simultaneously operating N transformation processes present a good example of a tight N cycle that is optimized for maximum N retention