Effects of Biochar on Fluxes and Turnover of Carbon in Boreal Forest Soils

Biochar has been used in different ecosystems to mitigate greenhouse gas emissions and increase C sequestration. However, the impacts of biochar addition in cold environments, such as boreal forests, are still poorly understood. We tested the effects of different addition rates (0, 5, and 10 Mg ha(-1)) of wood-derived biochar (pyrolysis temperature 650 degrees C) on the fluxes and turnover rates of soil C in a boreal forest in southern Finland. Biochar amendments significantly increased soil total organic C (TOC) stocks, C/N ratio, and moisture content, whereas the impacts of biochar on soil N concentration and the temperature sensitivity (Q(10)) of soil organic matter decomposition were not clear. Significantly lower values of TOC and total N (TN) were observed in the moss and organic layer in the 5 Mg ha(-1) biochar plots, however, in the mineral layer, there were no differences in C and N content between the treatments. We found a slight but statistically nonsignificant increase in soil respiration after biochar addition which increased with the amount of biochar added into the soil. However, the soil C turnover time was similar in biochar plots and control plots. We also observed a slight but statistically nonsignificant decrease in the instantaneous C fluxes normalized by the amount of C in the soil during the incubation which decreased with the application rates of biochar. Our results suggest that biochar addition doesn't accelerate the mineralization of soil organic C and could lead to larger stable C stocks in the surface soil layer. Thus, it seems that biochar is a promising tool to enhance the C sequestration in boreal forest soils.