NITROGEN FLUXES IN THROUGHFALL AND LITTERFALL IN TWO NOTHOFAGUS FORESTS IN SOUTHERN CHILE APORTES DE NITROGENO POR LA PRECIPITACION DIRECTA Y LA CAIDA DE HOJARASCA EN DOS BOSQUES DE NOTHOFAGUS EN EL SUR DE CHILE

Nitrogen return by leaf litterfall was compared with atmospheric nitrogen deposition for two deciduous Nothofagus stands in southern Chile, located in areas with contrasting land use. The litterfall return of nitrogen in a Nothofagus alpina (Poepp. et Endl.) Oerst. stand at San Pablo de Tregua, in the Cordillera de los Andes, was similar to the litterfall return in a Nothofagus obliqua (Mirb.) Oerst. stand at Paillaco, in the Central Depression. In contrast, the net throughfall and stemflow deposition differed significantly between the two stands. At San Pablo de Tregua, the annual bulk deposition of NH4+ and NO3- was significantly higher than the throughfall and stemflow deposition reaching the forest floor. This demonstrates an uptake of inorganic nitrogen by the aboveground biomass, which was correlated with month-to-month variation in the bulk inorganic nitrogen deposition by precipitation (r² > 0.73). At Paillaco, the canopy uptake of nitrogen was not directly detectable due to an estimated dry deposition input of 4-8 kg inorganic N ha-1 y-1. In both stands, nitrogen return through leaf litterfall (~ 50 kg N ha-1 y-1) was much higher than the atmospheric N deposition load (< 10 kg N ha-1 y-1). The results consequently confirm the low level of atmospheric pollution in the forests of this region. However, the clear difference in net throughfall deposition of inorganic nitrogen between the two stands suggests that the external N input by dry deposition may be considerably higher in the Central depression than in Cordillera de los Andes. More emphasis on monitoring dry atmospheric N deposition is a necessary tool for evaluating the consequences of future emission change