Robertson, S. J., Rutherford, P. M., López-Gutiérrez, J. C. and Massicotte, H. B. 2012. Biochar enhances seedling growth and alters root symbioses and properties of sub-boreal forest soils. Can. J. Soil Sci. 92: 329–340. Biochar application may enhance soil properties, improve plant productivity, and increase long-term carbon storage, but impacts of biochar on plant-microbe symbioses mediating plant nutrient uptake in temperate or boreal soils are not well known. We planted lodgepole pine (Pinus contorta var. latifolia) or sitka alder (Alnus viridis ssp. sinuata) seeds in pots containing field-collected forest soils (from central British Columbia) amended with 0, 5, or 10% (dry mass basis) biochar with and without urea fertilizer (150 mg N kg−1). Pine seedlings were harvested at 4 mo and roots were assessed for abundance and diversity of ectomycorrhizal (ECM) morphotypes using light microscopy and DNA sequencing. Biochar raised soil pH, exchangeable cations and cation exchange capacity in some treatments in both soils. Pine had greater biomass in biochar+fertilizer treatments compared to control and fertilizer-only treatments; this corresponded in part to an increase in abundance of some ECMs. Alder seedlings were harvested at 2, 3 and 4 mo to measure N fixation in root nodules using acetylene reductase assay (ARA). Alder seedlings had greater shoot biomass when grown in biochar-amended soils compared with unamended control. Although mean ARA rates (at 4 mo) were greater in biochar-amended soils compared with controls, the data showed great variation and differences were not statistically significant (P>0.05). This study showed that biochar addition can enhance soil properties and the early growth of pine and alder in some sub-boreal forest soils; small changes in ECM abundances may be expected.