Seasonal response of denitrifiers to temperature in a Quebec cropped soil

While some studies indicate no denitrification activity in early spring, others have demonstrated that denitrifiers from temperate region soils can adapt to low temperatures. The aim of the present paper was to study how seasonal changes in temperature affect denitrifying enzyme activity (DEA) in a cropped humic gleysol located in a cold temperate climate (Quebec). Soil was sampled monthly during a 16-mo period and DEA was measured at nine temperatures from 2 to 35 degrees C. A seasonal effect of temperature on DEA was significant at all incubation temperatures and was more important in November and in May-June. The effect of temperature on DEA Was better fitted with the square root model of Ratkowsky than with the Arrhenius equation. The regression coefficient b (Ratkowsky parameter) varied seasonally with a trend similar to that of DEA. These results show that the Ratkowsky model should be used instead of Arrhenius equation to describe the effect of cold temperature on denitrification.