Introduction

Seasonally frozen soils and permafrost are widespread on Earth, accounting for more than 50% of the Earth's land surface (Toll et al. 1999). Frozen soils have strong implications on freshwater hydrology, terrestrial ecology and the climatic system. For example, frozen soils are largely impervious to water, and during the release of water during spring, thaw may significantly increase runoff, contributing to severe flooding. In the last two decades, tundra soils and permafrost attracted serious attention from the entire global change community when it became clear that global warming is much more pronounced in the polar area than elsewhere. The climate projections suggest a continuation of the warming trend, with an increase in mean annual temperatures of 4-5°C by 2080 (Elberling and Brandt 2003; Callaghan et al. 2004). The thawing of permafrost, combined with melting of sea ice, is predicted to cause disastrous events including flooding, karst and erosion, accompanied by accelerated degradation of terrestrial carbon.

Microbiology of permafrost and frozen soils is at its infancy. Until recently, permafrost has been addressed by microbiologists primarily as a natural depository of ancient forms of life. However, the recent finding of measurable winter gas emission to the atmosphere (see below) demonstrated that subzero microbial activity is an important driver of the observed global changes. This activity may significantly accelerate permafrost degradation under global warming; and this acceleration should be detected well before the visible signs of permafrost thawing appear.

This review focuses on microbial activity in permafrost and frozen soils. The starting point will be methodology; how to measure subzero metabolic activity, and how to distinguish reliable data from experimental artifacts. This is followed by a survey of available data on spatial variation and magnitude of microbial activity in frozen soils, mainly in the North Slope of Alaska. Finally questions crucial for mechanistic understanding of subzero activity will be (tentatively) answered:

Nicolai S. Panikov

Thayer School of Engineering, Dartmouth College, 8000 Cummings, Hanover, NH 03755, USA [email protected]

R. Margesin (ed.) Permafrost Soils, Soil Biology 16,

DOI: 10.1007/978-3-540-69371-0, © Springer-Verlag Berlin Heidelberg 2009

- Is there mass-transfer between cells and frozen microenvironment?

- What kind of substrates are available to support subzero growth?

- What is the physiological state of active microorganisms: is it a partial dormancy, maintenance of viability without growth, or a regular metabolism resulting in cellular growth and division?

- What particular microbial species/phylotypes are responsible for subzero soil activity, what are their biological features and how can they be isolated from natural habitats?

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