Title: Effects of freeze-thaw events on arctic soil organisms



The aim of the project is to increase our understanding of the impact of freeze-thaw events on soil invertebrate populations, and their influence on decomposition processes in arctic soil ecosystems.



Soil fauna constitutes an important biotic component in arctic terrestrial ecosystems. Thus, their numbers and biomass may often be much higher than seen for temperate soil ecosystems. The main functional significance of soil fauna is regarded to be their impact on decomposition processes, and their contribution to the release of plant nutrients (e.g. nitrogen) to the soil. Through ingestion of soil organic matter and soil microbes the soil fauna controls the release of nutrients to plants in strongly nutrient-limited arctic ecosystems. However, in the high Arctic decomposition processes are very slow, and the soil fauna may also be important through interactions with cyanobacteria. Cyanobacteria are characteristic components of primary production in the high Arctic and play an important role in terrestrial ecosystems through their ability to fix atmospheric nitrogen that subsequently becomes available for higher plants. Many high arctic soil invertebrates (like most Collembola) depend to a great extent on cyanobacteria as food, and hence influence the turnover of cyanobacteria and the release of nitrogen to the soil through grazing. So far little is known about these processes, and there is a need for further studies to refine existing models of nutrient and carbon cycling in arctic ecosystems.


In the Arctic (e.g. Svalbard) a thick surface ice layer forms during mild autumns or winters with regular freeze thaw events or periods of freezing rain. Earlier studies have implicated this ice layer as being a major environmental catastrophe, especially for soil invertebrates. Freeze-thaw events may furthermore lead to death of soil microbes and cyanobacteria, with subsequent release of nutrients.  However, the nature of this constraint is little understood. Small increases in the average temperature in the Arctic due to global warming may result in an increased annual frequency of freeze-thaw events. The majority of field studies consider systems in balance and there have been few studies on the recovery of populations after severe disturbance due to stochastic environmental events.


Project description

The project comprises both laboratory and field studies. In the laboratory, controlled experiments manipulating the hydrological and thermal environment of mesocosms containing single species and species assemblies of important soil invertebrates collected at the chosen field sites will be performed. Such ecophysiological laboratory studies will be combined with field studies of populations in which hydrological and thermal conditions are manipulated using polythene greenhouses. In the field, faunal population dynamics and recovery, microbial biomass and nutrient mobilisation after freeze-thaw events will be studied. Existing long-term field manipulations of microclimate with shading screens, leaf litter addition and air and soil warming at heaths near Abisko Research Station in Northern Sweden, and the Large Scale Facility at Ny Aalesund, Svalbard, may be used as field locations. The successful applicant will be based at Dept. of Terrestrial Ecology, DMU, Silkeborg, with fieldwork in the Arctic and part of the laboratory work at University of Copenhagen.


Contact to:

Martin Holmstrup, Dept. of Terrestrial Ecology, DMU, Silkeborg, Phone +45 89291400;

e-mail [email protected]  


Anders Michelsen, Botanical Institute, Univ. of Copenhagen, Phone +45 35322270;

e-mail [email protected]