『Abstract
　Knowledge of the fate of deposited N in the possibly N-limited, highly biodiverse north Andean forests is important because of the possible effects of N inputs on plant performance and species composition. We analyzed concentrations and fluxes of NO3^--N, NH4⁺-N and dissolved organic N (DON) in rainfall, throughfall, litter leachate, mineral soil solution (0.15-0.30 m depths) and stream water in a montane forest in Ecuador during four consecutive quarters and used the natural ¹⁵N abundance in NO3^- during the passage of rain water through the ecosystem and bulk δ¹⁵N values in soil to detect N transformations. Depletion of ¹⁵N in NO3^- and increased NO3^--N fluxes during the passage through the canopy and the organic layer indicated nitrification in these compartments. During leaching from the organic layer to mineral soil and stream, NO3^- concentrations progressively decreased and were enriched in ¹⁵N but did not reach the δ¹⁵N values of solid phase organic matter (δ¹⁵N = 5,6-5.7‰). This suggested a combination of nitrification and denitrification in mineral soil. In the wettest quarter, the δ¹⁵N value of NO3^- in litter leachate was smaller (δ¹⁵N = -1.58‰) than in the other quarters (δ¹⁵N = -9.38±SE 0.46‰) probably because of reduced mineralization and associated fractionation against ¹⁵N. Nitrogen isotope fractionation of NO3^- between litter leachate and stream water was smaller in the wettest period than in the other periods probably because of a higher rate of denitrification and continuous dilution by isotopically higher NO3^--N from throughfall and nitrification in the organic layer during the wettest period. The stable N isotope composition of NO3^- gave valuable indications of N transformations during the passage of water through the forest ecosystem from rainfall to the stream.

Keywords: Denitrification; ¹⁵N natural abundance; Nitrate; Nitrification; Terrestrial N cycling; Tropical montane forest』

Abbreviations
Introduction
Study site
Materials and methods
　Sampling
　Chemical analyses
　Calculations and statistical tests
Results
　Nitrogen concentrations, C:N ratios and δ¹⁵N value of soils
　Dissolved N concentrations and fluxes
　δ¹⁵N values of dissolved NO3^- in ecosystem fluxes
Discussion
　Shifts of δ¹⁵N values as indicator of N transformations
　Seasonal variability of N transformations
Conclusions
Acknowledgments
References