Keywords: Forest floor Greenhouse gas

a b s t r a c t Considerable progress has been made in understanding the impacts of soil frost on carbon (C) and nitrogen (N) cycling, but the effects of soil frost on C and N fluxes during snowmelt remain poorly understood. We conducted a laboratory experiment to determine the effects of soil frost on C and N fluxes from forest floor soils during snowmelt. Soil coreswere collected froma sugarmaple (Acer saccharum)eAmerican beech (Fagus grandifolia) and a red spruce (Picea rubens)ebalsam fir (Abies balsamea) forest at the Hubbard Brook Experimental Forest in New Hampshire, U.S.A. Soils were exposed to one of three temperature treatments, including severe (15 C), mild (0.5 C), and no soil frost (þ5 C) conditions. After oneweek the soils were incubated atþ5 C and snowwas placed on top of the soils to simulate spring snowmelt. NO3 losseswere up to 5.5 mg N kg1 soil greater in the mild soil frost treatment than the severe soil frost treatment. Net losses of NH4þ andDON in leachatewere up to 19 and18mgNkg1 soil greater in the no soil frost andmild soil frost treatments, respectively, than the severe soil frost treatment. In contrast, soil frost did not have a significant impact on dissolved organic C or cumulative gaseous fluxes of C and N throughout the snowmelt period. However, the total cumulative flux of C (i.e. dissolved organic C þ CO2 þ CH4) and N (i.e. dissolved organic N þ NH4 þ NO3 þ N2O) in the severe soil frost treatment were between one quarter and one half tha