Season-Dependent Effect of Fire-Derived Charcoal on the Above- and Belowground Litter Decomposition in Boreal Forests

Fire-derived charcoal (charcoal) is a stable byproduct of forest fires, which accumulates in the litter layer and soils of boreal forests. Therefore, the decomposition of litter and roots as one of the key processes in the carbon cycle in the soils of northern forests proceeds almost everywhere in the presence of charcoal. To date, the data on the influence of charcoal on the organic material decomposition in boreal forests are extremely scarce and most of them do not consider the cold period, which lasts on the average half a year in this zone. The goal of this work is to determine the seasonal influence of charcoal on the decomposition of plant litter of different qualities (larch needles, birch leaves, grasses, and mixtures of these litter types) on the soil surface and the roots of the same types in the soil. A field litterbag experiment demonstrates that charcoal accelerates the decomposition of litter in a species-specific manner. Charcoal accelerates the mass loss of recalcitrant aboveground litter (needles) and all types of roots during the cold season. As for the warm season, charcoal accelerates the decomposition of only needles and has no effect on the roots. Thus, our study shows a greater influence of charcoal on the subsoil decomposition especially in the cold season. The seasonal influence of charcoal is demonstrated for the first time and should be taken into account as an important factor of humus formation and carbon dynamics in the soils of boreal forests.