Metla Project 640055

Reindeer grazing and tundra soil carbon storage under changing climate

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Duration: 2009-2014   Keywords: arctic, carbon balance, global change, microbial activity, reindeer husbandry
Research Programme: Functioning of forest ecosystems and use of forest resources in changing climate

Objectives

It is currently predicted that soil carbon storage in terrestrial tundra ecosystems will decrease as a result of global change and by this way, tundra soils will contribute to the increase in atmospheric carbon dioxide. Grazing by the reindeer (Rangifer tarandus) considerably shapes both the structure of tundra vegetation and vegetation responses to global change, but it remains unknown how grazing interacts with the effects of global change on soil carbon storage. Current vegetation theory states that tundra vegetation has two alternate steady states, the ungrazed tundra with domination of slow-growing dwarf shrubs, and the grazed tundra with domination of graminoids. The research project will compare effects of global change on plant growth and decomposition of soil organic matter, which are important determinants of the soil carbon stocks, between the alternate steady states, and utilize long-term reindeer pasture rotation fences, which separate large districts to areas in which grazing has been excluded, and to areas which have been intensively grazed. In these areas, the slow processes of vegetation shift into another alternate state, and accumulation of soil carbon under the different vegetation, have both taken place. A large field experiment with experimental warming and fertilization will be conducted to test hypotheses that reindeer grazing diminishes effects of global warming on decomposition rates of accumulated soil organic matter. This hypothesis is based on recent findings that soil organic matter is more recalcitrant under grazed tundra than that in the ungrazed tundra, and on the finding that grazing alleviates nitrogen-limitation of microbial enzyme activity and growth rates, which in ungrazed conditions have major feedback effect on microbial activity in tundra systems. Treatment effects are verified with analyses of decomposition rates and activity, biomass and community of soil microorganisms together with measurements of litter production. Temperature-dependence of decomposition and degradation potential of soil microbial communities will also be investigated by laboratory experiments. The project results are expected to reform predictions on ecosystem responses to global change. Results will also give new insights into the herbivore-plant-soil –interactions and the basic mechanisms of soil carbon sequestration.

Project leader: Stark, Sari

Other researchers: Martz, Francoise, RO (2011-12), Väisänen, Maria (2010-12)


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Updated 02.02.2013
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