Boczulak, S. A., Hawkins, B. J., Maynard, D. G. and Roy, R. 2015. Long- and short-term temperature differences affect organic and inorganic nitrogen availability in forest soils. Can. J. Soil Sci. 95: 77-86. Soil microbial activity determines rates of decomposition and is strongly influenced by temperature. Soil microbial communities may be adapted to site characteristics, including temperature, through physiological modification of microbial populations or changes in species composition; however, response to short-term changes in temperature may also occur. We searched for evidence of short- and long-term temperature response of microbial communities involved in soil nitrogen (N) cycling by measuring the relative availability of organic and inorganic N forms in forest soils from a high and a low elevation site, incubated at 10, 16 and 20°C for 16 wk. By week 16, ammonium concentrations were greater in soils incubated at 16 and 20°C than at 10°C, and in soil from the low elevation site, compared with high elevation. Nitrate concentrations increased in soil from the low elevation site incubated at 16 and 20°C, but changed little in other treatments. Assessment of autotrophic nitrification potential showed gross nitrification in soil from the low elevation site was likely from classical chemolithotrophic nitrifiers. Organic N concentration increased over time in the 16 and 20°C incubations of soil from the low elevation site, but only increased in the 20°C treatment for soil from the high elevation site. Long-lasting site effects were indicated by the more active microbial community in soil from low elevation, which could be related to site temperature. Evidence of short-term temperature response of N cycling processes was observed in soils from both elevations.