Soil microbial responses over 2 years following biochar addition to a north temperate forest

Soil microbial biomass, activity, and community composition were studied 1 and 2 years after biochar, phosphorus (P), and biochar + P additions to the soil of a north temperate, mixed-deciduous, P-limited forest in Central Ontario, Canada. Biochar was pyrolyzed on site from sugar maple and white spruce sawdust at ca. 400 A degrees C, and P was added as triple superphosphate. Biochar additions of 5 t ha(-1) (approximately 0.4 to 1 kg P ha(-1)) had minor effects on bacterial and fungal community composition, fungi/bacteria ratios, microbial biomass, and microbial C mineralization, with significant changes only being detected in the organic layer for additions of maple biochar. In contrast, additions of 200 kg P ha(-1) did alter soil chemical properties and reduced both microbial biomass and fungi/bacteria ratios. We conclude that biochar addition at 5 t ha(-1) is neither beneficial nor toxic to the soil microbes in a northern hardwood forest on acidic soils, suggesting that biochar amendments can be used to sequester C without adversely affecting the soil microbial community.