Snow removal and its influence on temperature and N dynamics in alpine soils (Vallee d'Aoste, northwest Italy)

The effect of a lack of snow cover in winter was investigated in two soils, beneath larch and meadow, in NW Italy (Vallee d'Aoste Region). During the late 1980s and early 1990s and 2000s, this region experienced extreme climatic conditions including a low snow pack and lack of snow cover for extended periods with important effects on soil temperature and nutrient dynamics. In particular, the mountain belt in the Alps may be extremely sensitive to these phenomena, in relation to the rise in average snowline projected under a warmer global climate. The study area is located at an elevation of 1450 m asl in the Italian Alps (Mont Mars Natural Reserve). During the winter 2003/04, snow was continuously removed in a treatment plot while a reference plot was maintained undisturbed. Soil temperature was measured at 10 cm depth by data loggers (UTL-1). Soil N transformations in the topsoil (10 cm depth) were determined by the buried-bag technique. The removal of the snow cover caused a significant decrease in soil temperature, related to concurrent decreases in air temperature. The lowest soil temperatures recorded were -4.3 degrees C and -4.5 degrees C beneath larch and meadow, respectively, on January 31, 2004. Soil temperature in the undisturbed plots was maintained above the freezing point when the snow cover was present. The snow removal caused significant increases in net ammonification in both soils and net nitrification only under meadow, but did not affect microbial biomass N which decreased in both plots. Our results suggest that the lower temperature reached in the plot without snow favored the production of inorganic N by physical rather than microbial degradation of soil organic matter (SOM). Soil freezing could enhance soil-aggregate disruption releasing physically protected SOM and fragmentation of OM itself.