New paper by Aaltonen et al., 2019 determines how heterotrophic soil respiration (Rh), originating from the decomposition of SOM, and the Q10 of this process vary between different depths over the years following a forest fire in permafrost-affected soils. How the microbial biomass and qCO2 are affected by the fire, and what are the most important factors affecting the Q10 of SOM decomposition.

The results indicate that forest fires may facilitate the decomposition of permafrost SOM by increasing the active layer depth, but on the same time fire increased the temperature sensitivity of decomposition. The SOM in the permafrost surface was less temperature sensitive than the SOM in the soil surface. The post-fire decreases in ground vegetation were reflected in the SOM temperature sensitivity shortly after fire but seemed to return to original levels with forest succession.

The fire also increased the microbial qCO2, and these changes partly explain the lack of significant decrease in heterotrophic soil respiration after fire, as the microbes may use more C for respiration in the recently burned areas compared with the older areas. Even though fires increased the active layer depth, the decrease in SOM quality caused by fire may limit the decomposition rate to some degree.