In eastern Canada, climate change-related warming and increased precipitation may alter winter snow cover, with potential consequences for soil conditions, nitrogen (N) cycling, and microbes. We conducted a 2-year field study aimed at determining the influence of snow removal, snow accumulation, and ambient snow in a potato-barley crop system on the abundance and expression of denitrifier (nirS, nirK, nosZ) and nitrifier (ammonium oxidizing archaeal (AOA) and bacterial (AOB) amoA) genes. Denitrifier and nitrifier abundance and expression results were compared to N2O production, soil atmosphere accumulation, and surface fluxes. In the first winter, nirK abundance was lowest while AOB abundance was greatest in snow accumulation treatments. In the second winter, greatest abundances were observed in the ambient snow treatment, which had greatest N2O accumulation and spring thaw fluxes, suggesting a link between microbial populations and biogeochemical functioning. Treatment effects on gene expression were limited, but greatest AOA, AOB, and nosZ expression was measured near 0 degrees C and above 15 degrees C, indicating that activity was promoted by freeze-thaw conditions and at summer temperatures. Overall, effects of changing snow depth on denitrifier and nitrifier abundance were not solely due to change in soil temperature, but also to soil moisture and/or interactions between these parameters.

Diurnal freeze-thaw cycles (FTCs) occur in the spring and autumn in boreal wetlands as soil temperatures rise above freezing during the day and fall belowfreezing at night. A surge inmethane emissions fromthese systems is frequently documented during spring FTCs, accounting for a large portion of annual emissions. In boreal wetlands, methane is produced as a result of syntrophicmicrobial processes, mediated by a consortiumof fermenting bacteria and methanogenic archaea. Further research is needed to determine whether FTCs enhance microbial metabolism related tomethane production through the cryogenic decomposition of soil organicmatter. Previous studies observed large methane emissions during the spring thawed period in the Sanjiang seasonal frozen marsh of Northeast China. To investigate how FTCs impact the soilmicrobial community and methanogen abundance and activity, we collected soil cores from the Sanjiang marsh during the FTCs of autumn 2014 and spring 2015. Methanogens were investigated based on expression level of themethyl coenzyme reductase (mcrA) gene, and soil bacterial and archaeal community structures were assessed by 16S rRNA gene sequencing. The results show that a decrease in bacteria and methanogens followed autumns FTCs, whereas an increase in bacteria and methanogens was observed following spring FTCs. The bacterial community structure, including Firmicutes and certain Deltaproteobacteria, was changed following autumn FTCs. Temperature and substrate were the primary factors regulating the abundance and composition of the microbial communities during autumn FTCs, whereas no factors significantly contributing to spring FTCs were identified. Acetoclastic methanogens from order Methanosarcinales were the dominant group at the beginning and end of both the autumn and spring FTCs. Active methanogens were significantly more abundant during the diurnal thawed period, indicating that the increasing number of FTCs predicted to occur with global climate change could potentially promote CH4 emissions in seasonal frozen marshes. (c) 2018 Elsevier B.V. All rights reserved.