Snow removal and its influence on temperature and N dynamics in alpine soils (Vallée 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 10cm depth by data loggers (UTL-1). Soil N transformations in the topsoil (10cm 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°C and -4.5°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.

[1]  K. Tonnessen,et al.  Mineral nitrogen transformations in and under seasonal snow in a high-elevation catchment , 1996 .

[2]  E. Bochove,et al.  Effects of freeze-thaw and soil structure on nitrous oxide produced in a clay soil , 2000 .

[3]  R. Monson,et al.  Carbon availability and temperature control the post-snowmelt decline in alpine soil microbial biomass , 2000 .

[4]  P. Brooks,et al.  Microbial activity under alpine snowpacks, Niwot Ridge, Colorado , 1996 .

[5]  Charles T. Driscoll,et al.  Soil Freezing and the Acid-Base Chemistry of Soil Solutions in a Northern Hardwood Forest , 2003 .

[6]  Deane Wang,et al.  Snow Removal and Ambient Air Temperature Effects on Forest Soil Temperatures in Northern Vermont , 2003 .

[7]  J. Bauhus,et al.  Mechanisms for carbon and nutrient release and retention in beech forest gaps , 2004, Plant and Soil.

[8]  T. Appel.  Non-biomass soil organic N — the substrate for N mineralization flushes following soil drying–rewetting and for organic N rendered CaCl2-extractable upon soil drying , 1998 .

[9]  P. Hazlett,et al.  Temporal Variation in Nitrate and Nutrient Cations in Drainage Waters from a Deciduous Forest , 1989 .

[10]  A. Michelsen,et al.  Mineralization and distribution of nutrients in plants and microbes in four arctic ecosystems: responses to warming , 2002, Plant and Soil.

[11]  Charles T. Driscoll,et al.  Colder soils in a warmer world: A snow manipulation study in a northern hardwood forest ecosystem , 2001 .

[12]  P. Groffman,et al.  Snow depth manipulation and its influence on soil frost and water dynamics in a northern hardwood forest , 2001 .

[13]  J. Schimel,et al.  Microbial activity of tundra and taiga soils at sub-zero temperatures , 1995 .

[14]  D. Hertel,et al.  Effects of experimental soil frost on the fine‐root system of mature Norway spruce , 2008 .

[15]  P. Groffman,et al.  Snow depth, soil frost and nutrient loss in a northern hardwood forest , 1999 .

[16]  G. Robitaille,et al.  Increased soil nitrate losses under mature sugar maple trees affected by experimentally induced deep frost , 1995 .

[17]  W. C. Hinman.  EFFECTS OF FREEZING AND THAWING ON SOME CHEMICAL PROPERTIES OF THREE SOILS , 1970 .

[18]  J. Fyles,et al.  Effect of snow removal on leaf water potential, soil moisture, leaf and soil nutrient status and leaf peroxidase activity of sugar maple , 1994, Plant and Soil.

[19]  A. Edwards,et al.  Simulating soil freeze/thaw cycles typical of winter alpine conditions: Implications for N and P availability , 2007 .

[20]  H. Henry.  Soil freeze–thaw cycle experiments: Trends, methodological weaknesses and suggested improvements , 2007 .

[21]  J. Harte,et al.  Effects of manipulated soil microclimate on mesofaunal biomass and diversity , 1996 .

[22]  M. Hill,et al.  A procedure for the simultaneous oxidation of total soluble nitrogen and phosphorus in extracts of fresh and fumigated soils and litters , 1995 .

[23]  K. Larsen,et al.  Repeated freeze-thaw cycles and their effects on biological processes in two arctic ecosystem types , 2002 .

[24]  E. Witter,et al.  Sources of C and N contributing to the flush in mineralization upon freeze–thaw cycles in soils , 2002 .

[25]  V. Huhta,et al.  Effects of hard frost and freeze-thaw cycles on decomposer communities and N mineralisation in boreal forest soil , 2003 .

[26]  C. F. Eno,et al.  Nitrate Production in the Field by Incubating the Soil in Polyethylene Bags , 1960 .

[27]  W. E. Simpson,et al.  Determination of ammonium in Kjeldahl digests of crops by an automated procedure , 1971 .

[28]  R. Littler,et al.  Soil microbial biomass: Influence of simulated temperature changes on size, activity and nutrient-content , 1989 .

[29]  T. Öztaş,et al.  Effect of freezing and thawing processes on soil aggregate stability , 2003 .

[30]  J. Goksøyr,et al.  Respiratory burst after freezing and thawing of soil: Experiments with soil bacteria , 1988 .

[31]  P. Brookes,et al.  Chloroform fumigation and the release of soil nitrogen: A rapid direct extraction method to measure microbial biomass nitrogen in soil , 1985 .

[32]  W. Borken,et al.  Do freeze‐thaw events enhance C and N losses from soils of different ecosystems? A review , 2008 .

[33]  A. Edwards,et al.  Freezing and Its Effect on Chemical and Biological Properties of Soil , 1992 .

[34]  M. Beniston.  Climatic Change in Mountain Regions: A Review of Possible Impacts , 2003 .

[35]  P. Groffman,et al.  Effects of mild winter freezing on soil nitrogen and carbon dynamics in a northern hardwood forest , 2001 .

[36]  P. Brooks,et al.  Snowpack controls on nitrogen cycling and export in seasonally snow-covered catchments , 1999 .

[37]  T. Moore.  LITTER DECOMPOSITION IN A SUBARCTIC SPRUCE-LICHEN WOODLAND, EASTERN CANADA' , 1984 .

[38]  A. Edwards,et al.  Labile nitrogen, carbon, and phosphorus pools and nitrogen mineralization and immobilization rates at low temperatures in seasonally snow-covered soils , 2007, Biology and Fertility of Soils.

[39]  R. Joergensen,et al.  C and net N mineralisation in a coniferous forest soil: the contribution of the temporal variability of microbial biomass C and N , 2002 .

[40]  P. Brooks,et al.  Winter production of CO2 and N2O from alpine tundra: environmental controls and relationship to inter-system C and N fluxes , 1997, Oecologia.

[41]  G. Sparling,et al.  Microbial biomass carbon and readily mineralized nitrogen in peat and forest humus , 1988 .

[42]  A. Michelsen,et al.  Effects of freeze–thaw cycles on microarthropods and nutrient availability in a sub-Arctic soil , 2005 .

[43]  G. McCarty,et al.  Effect of freeze-thaw events on mineralization of soil nitrogen , 1992, Biology and Fertility of Soils.

[44]  W. Borken,et al.  Long‐term development of nitrogen fluxes in a coniferous ecosystem: Does soil freezing trigger nitrate leaching? , 2007 .

[45]  A. Michelsen,et al.  Mineralization and microbial immobilization of N and P in arctic soils in relation to season, temperature and nutrient amendment , 1999 .

[46]  Riccardo Scalenghe,et al.  Changes in the seasonal snow cover of alpine regions and its effect on soil processes: A review , 2007 .