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

Abstract

Core Ideas We tested the effects of different addition rates (0, 0.5, and 1.0 kg m−2) of wood‐derived biochar (pyrolysis temperatures 650°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 stocks, C/N ratio, and moisture content, whereas the impacts of biochar on soil N concentration and temperature sensitivity (Q10) of soil organic matter decomposition were not clear. 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. 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°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 (Q10) 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.