The effects of long and short soil freezing-defrosting cycles on nitrifying microbial activity

An incubation experiment was conducted on chestnut soil microcosms to assess the impact of long and short cold shock on the rate of nitrification of ammonium-oxidizing bacteria and archaea. Significant reduction of nitrifying activity was observed after 2 weeks of cold shock, while 24-hour incubation at a low temperature did not affect the rate of nitrification of microorganisms. We assume that the prevalence of psychrophiles or mesophiles with a broad range of adaptation in the chestnut soil helps maintain a high level of nitrification in conditions of frequent fluctuations of high and low temperatures. Decreasing nitrifying activity after long freezing points to the death of a small pool of the least resistant organisms, which is associated with the peculiarities of the geographical location of chestnut soils and lack of long periods of soil freezing. The composition of communities of bacteria and archaea in the course of the experiments did not change, which was determined by denaturing gel electrophoresis (DGGE).