NITROGEN FLUXES IN A NOTHOFAGUS OBLIQUA FOREST AND A PINUS RADIATA PLANTATION IN THE CENTRAL VALLEY OF SOUTHERN CHILE

Forest structure and tree species can have a significant impact on total atmospheric nitrogen (N) deposition; for example, deciduous forests have higher N requirements than coniferous forests. However, knowledge about the effect of the conversion of native Chilean vegetation cover by exotic plantations on N cycling is scarce. The aim of this study was to determine the effect of the replacement of a Nothofagus obliqua native forest by a Pinus radiata plantation in southern Chile on the chemistry of throughfall, stemflow, soil water infiltration and percolation. Pinus radiata stemflow was more acidic (pH 4.7) than precipitation (pH 5.2) and throughfall (pH 5.6), while in the Nothofagus forest stemflow and throughfall pH were 6.3 and 6.1, respectively. In the Nothofagus forest, the soil water infiltration and percolation at 150 cm depth pH were 6.2 and 6.3, while in the Pinus plantation pH were 5.9 and 6.0, respectively. Throughfall and stemflow were enriched in DIN (NH4+-N + NO3--N) and DON in both forests. DIN fluxes were higher in throughfall in the Nothofagus forest (7.5 kg ha-1 yr-1) than in the Pinus plantation (6.4 kg ha-1 yr-1). DIN infiltration fluxes were much higher in the Pinus plantation (NH4+-N = 3.1 kg ha-1 yr-1, NO3--N = 5.4 kg ha-1 yr-1) than in the Nothofagus forest (NH4+-N = 0.4 kg ha-1 yr-1, NO3--N = 1.5 kg ha-1 yr-1), suggesting a lower N immobilization and/or plant uptake in the Pinus plantation