ORIGINAL PAPER Labile nitrogen, carbon, and phosphorus pools and nitrogen mineralization and immobilization rates at low temperatures in seasonally snow-covered soils Michele Freppaz & Berwyn L. Williams & Anthony C. Edwards & Riccardo Scalenghe & Ermanno Zanini Received: 14 December 2005 / Revised: 23 June 2006 / Accepted: 28 June 2006 / Published online: 22 August 2006 # Springer-Verlag 2006 Abstract Surface mineral horizons from four ecosystems sampled in the northwestern Italian Alps were incubated at -3 and +3°C to simulate subnivial and early thaw period temperatures for a seasonally snow-covered area. The soil profiles at these sites represent extreme examples of management, grazed meadow (site M) and extensive grazing beneath larch (site L) or naturally disturbed by avalanche and colonized by alder (site A) and the expected forest climax vegetation beneath fir (site F). Changes in labile pools of nitrogen (N) and phosphorus (P) were active at all sites at both temperatures during 14 days of laboratory incubation. Ammonium was the dominant inorganic form of total dissolved N (TDN), being equivalent to 1.8–9.8 g N m -2 within the mineral horizon. Gross rates of ammonification were similar at the two temperatures but significantly (p<0.05) greater in soil from beneath fir than in the other three. Nitrification occurred in all soils and displayed a wide range in rates, from 2 to 85 mg N m -2 day -1 , and was least in the two most acid soils, A and F. Immobilization of NH 4 + as microbial N was greater in the fir soil than in the other three. Also, the fir soil showed greatest gross ammonification and least accumulation of NO 3 - and greatest tendency to retain N. This high N retention capacity in the climax ecosystem contrasted with the managed systems characterized by higher nitrification rates and greater potential spring NO 3 - loss. Dissolved organic N ranged between 30 and 50% of the TDN, while dissolved organic P was greater than 70% of total dissolved P (TDP). The dissolved organic compounds were important components of the labile pool, in equilibrium with a large reserve of organic N, and may significantly contribute to the soil N availability at low temperatures. Keywords Ammonification . Dissolved organic nitrogen . N immobilization . Nitrification . Phosphorus Sub-alpine soils . Land management Introduction Seasonally snow-covered mountainous regions experience extended periods of low temperatures that influence pedo- genic processes, biological activity, and vegetation cover. Emphasis has generally been given to understanding nutrient cycling during the period of active growth; however, there is evidence from both in situ and in vitro studies that nutrients can be actively cycled during the so-called “dormant” winter period (Salisbury 1985; Brooks et al. 1996). It has further been suggested that the long-term sustainability of some of these ecosystems might partially rely upon the efficiency of nutrient retention determined from the balance between mineralization and immobilization (Brooks and Williams 1999). Poor nutrient immobilization/retention capabilities may induce conditions that allow an excessive flux of nutrients during the spring thaw period (Brooks et al. 1998), depleting the nutrient capital of the system. Biol Fertil Soils (2007) 43:519–529 DOI 10.1007/s00374-006-0130-5 M. Freppaz (*) : E. Zanini DIVAPRA—Chimica Agraria, Laboratorio Neve e Suoli Alpini, Università di Torino, 44 Via Leonardo da Vinci, 10095 Grugliasco, Italy e-mail: michele.freppaz@unito.it B. L. Williams : A. C. Edwards Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, UK R. Scalenghe DAAT, Università di Palermo, 13 Viale delle Scienze, 90128 Palermo, Italy