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Temperature sensitivity of soil organic matter decomposition after forest fire in Canadian permafrost region

Aaltonen, Heidi, Palviainen, Marjo, Zhou, Xuan, Köster, Egle, Berninger, Frank, Pumpanen, Jukka, Köster, Kajar
Journal of environmental management 2019 v.241 pp. 637-644
carbon dioxide, ecosystems, forest fires, forest stands, forest succession, global warming, greenhouse gas emissions, long term effects, permafrost, soil carbon, soil microorganisms, soil organic matter, soil respiration, soil sampling, soil temperature, thawing, Arctic region, Canada
Climate warming in arctic/subarctic ecosystems will result in increased frequency of forest fires, elevated soil temperatures and thawing of permafrost, which have implications for soil organic matter (SOM) decomposition rates, the CO2 emissions and globally significant soil C stocks in this region. It is still unclear how decomposability and temperature sensitivity of SOM varies in different depths and different stages of succession following forest fire in permafrost regions and studies on long term effects of forest fires in these areas are lacking. To study this question, we took soil samples from 5, 10 and 30 cm depths from forest stands in Northwest Canada, underlain by permafrost, that were burnt by wildfire 3, 25 and over 100 years ago. We measured heterotrophic soil respiration at 1, 7, 13 and 19 °C. Fire had a significant effect on the active layer depth, and it increased the temperature sensitivity (Q10) of respiration in the surface (5 cm) and in the deepest soil layer (30 cm) in the 3-year-old area compared to the 25- and more than 100-year-old areas. Also the metabolic quotient (qCO2) of soil microbes was increased after fire. Though fires may facilitate the SOM decomposition by increasing active layer depth, they also decreased SOM quality, which may limit the rate of decomposition. After fire all of these changes reverted back to original levels with forest succession.