Influences of over winter conditions on denitrification and nitrous oxide-producing microorganism abundance and structure in an agricultural soil amended with different nitrogen sources

Changes in nitrifier and denitrifier abundance, composition and nitrous oxide (N2O) emissions during the winter period in soils with spring application of nitrogen (N) as mineral fertilizer, cattle manure or poultry manure were evaluated. Soil samples were collected from an agricultural field in Eastern Canada during winters of 2009–2010 and 2010–2011. Surprisingly, N2O emission rates were up to 150 fold greater in the coldest dates compared to other dates for the two winters, however rates were similar among N sources. Abundance of nitrifiers (Nitrobacter-like nxrA, archaeal amoA) and denitrifiers (nirK, nirS) increased in March and April compared with other sampling dates. Nitrifier abundance (nxrA) was the greatest in soils amended with cattle manure, while denitrifiers (nirK, nirS) were more abundant in soils amended with poultry manure. Nitrifiers and denitrifiers showed different composition depending on sampling date and N sources in the two winters, suggesting that changes in environmental conditions and N sources both influenced these communities. Our findings demonstrate that N2O emissions occur at significant rates in snow covered agricultural soils. Moreover, the abundance and diversity of denitrifier and nitrifier communities evolved throughout winter and appeared to be influenced by soil conditions and N sources applied in the previous spring.