Alpine snow molds and sub-nivian ecology

Background/Question/Methods

Microbial activity, as recorded by respired CO₂, increases exponentially under the late-winter snow pack in sub-alpine forests of the Rocky Mountains.  It has been estimated that up to half of the carbon fixed during the growing season is respired back to the atmosphere under the snow during the winter and early spring.  We have recently identified and isolated some of the microorganisms responsible for this rapid decomposition that occurs under the snow. Fungi were isolated from alpine forest soils over a period of three years by inoculating plated media utilizing carbon sources common in the alpine areas where the fungi are found.  Isolations were done at low temperatures (below 4°C) with successive sub-culturing yielding pure isolates.  The fungi were identified by PCR and SSrDNA sequencing.

Results/Conclusions

The isolates that grew the fastest at low temperatures were identified as Zygomycota from the Mortierellales and Mucorales orders.  These fungi could grow exponentially at temperatures down to -3ºC (the lowest temperature tested) and none could grow at temperatures above 23ºC.  Their exponential growth rates were much higher than previously documented for fungal growth below 0°C or rates of exponential CO₂ flux through the late-winter snow pack.  Some of the isolates also exhibited very high Q₁₀ values (>100) across the temperature range of -3 to 4°C.  The kinetic behavior of these fungi at low temperatures provides the basis for a more mechanistic understanding of late winter CO₂ fluxes from snow covered soils.