ORIGINAL ARTICLE Phylogeny and Ecophysiology of Opportunistic “Snow Molds” from a Subalpine Forest Ecosystem S. K. Schmidt & K. L. Wilson & A. F. Meyer & M. M. Gebauer & A. J. King Received: 19 September 2007 / Accepted: 25 February 2008 / Published online: 29 April 2008 # Springer Science + Business Media, LLC 2008 Abstract Mats of coenocytic “snow molds” are commonly observed covering the soil and litter of alpine and subalpine areas immediately following snow melt. Here, we describe the phylogenetic placement, growth rates, and metabolic potential of cold-adapted fungi from under-snow mats in the subalpine forests of Colorado. SSU rDNA sequencing revealed that these fungi belong to the zygomycete orders Mucorales and Mortierellales. All of the isolates could grow at temperatures observed under the snow at our sites (0°C and −2°C) but were unable to grow at temperatures above 25°C and were unable to grow anaerobically. Growth rates for these fungi were very high at −2°C, approximately an order of magnitude faster than previously studied cold- tolerant fungi from Antarctic soils. Given the rapid aerobic growth of these fungi at low temperatures, we propose that they are uniquely adapted to take advantage of the flush of nutrient that occurs at the soil–snow interface beneath late winter snow packs. In addition, extracellular enzyme produc- tion was relatively high for the Mucorales, but quite low for the Mortierellales, perhaps indicating some niche separation between these fungi beneath the late winter snow pack. Introduction Recent research in alpine and subalpine ecosystems has revealed that microbes are abundant and active under late winter snow packs [13, 23]. The subnivian environment is ideal for the growth of cold-loving and cold-tolerant microbes due to prolonged periods of stable temperatures and abundant moisture [11]. In fact, it is very common to observe mats of “snow mold” covering plant litter and soil as snow banks recede in the spring at alpine and sub-alpine sites in the Rocky Mountains [22]. These fungal communities are ephemeral and rapidly disappear once the snow is gone. We know very little about the types of fungi that function during the final months of snow cover in seasonally snow- covered environments. Environmental clone libraries of under-snow soils from alpine tundra and subalpine forests have revealed many fungal groups that may be unique to the under-snow environment and some that have never been cultured [15, 21]. These fungi may contribute substantially to biogeochemical fluxes beneath the snow and understanding their physiologies could lend important insight into how global biogeochemical cycles will change as global warming affects both the duration and depth of snow packs over much of the Earth. For example, biogeochemical studies of subalpine forest soils in Colorado have shown that microbial communities are very active under the late winter snow pack resulting in high levels of extracellular enzyme activity and CO 2 fluxes from snow-covered soils [16, 28]. At these same sites, we have consistently observed mats of snow mold covering the ground as the snow banks recede. Here, we describe initial studies of the phylogenetics and physiology of several fungi that were isolated at low temperatures from samples of the under-snow fungal mats. Materials and Methods Study Site The study site is at 3,050 m above sea level 25 km west of Boulder, Colorado (40°1′58′N; 105°32′47′W) near the Microb Ecol (2008) 56:681–687 DOI 10.1007/s00248-008-9387-6 S. K. Schmidt (*) : K. L. Wilson : A. F. Meyer : M. M. Gebauer : A. J. King Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309, USA e-mail: steve.schmidt@colorado.edu