Physical mixing between humus and mineral matter found in cryoturbated soils increases short-term heterotrophic respiration rates

Cryoturbation is an important mechanism in the most recent large-scale model describing the build-up of soil organic carbon (SOC) in arctic soils. In this paper, we hypothesize that the physical mixing of humus and mineral soil generated by this process causes previously unconsidered effects on respiration rates. Through laboratory incubations we found that mixing of humus into mineral soil from cryoturbated soils primed heterotrophic respiration rates by about 40%, which was of the same magnitude as the effect generated by a rise in soil temperature from 5 °C to 10 °C. Our result indicates that cryogenic mixing, if complete, may generate short-term positive effects on heterotrophic respiration rates as long as the mixing does not translocate carbon into much colder soil layers. ► Physical soil mixing increases heterotrophic respiration rates in arctic soils. ► This priming effect is more important at low temperatures. ► This priming effect is an unconsidered effect of cryoturbation.