Field-Scale Pattern of Denitrifying Microorganisms and N₂O Emission Rates Indicate a High Potential for Complete Denitrification in an Agriculturally Used Organic Soil

More than 50% of all anthropogenic N₂O emissions come from the soil. Drained Histosols that are used for agricultural purposes are particularly potent sources of denitrification due to higher stocks of organic matter and fertiliser application. However, conditions that favour denitrification can vary considerably across a field and change significantly throughout the year. Spatial and temporal denitrifier dynamics were assessed in a drained, intensely managed Histosol by focusing on the genetic nitrite and N₂O reduction potential derived from the abundance of nirK, nirS and nosZ genes. These data were correlated with soil properties at two different points in time in 2013. N₂O emissions were measured every 2 weeks over three vegetation periods (2012–2014). Very low N₂O emission rates were measured throughout the entire period of investigation in accordance with the geostatistical data that revealed an abundance of microbes carrying the N₂O reductase gene nosZ. This, along with neutral soil pH values, is indicative of high microbial denitrification potential. While the distribution of the microbial communities was strongly influenced by total organic carbon and nitrogen pools in March, the spatial distribution pattern was not related to the distribution of soil properties in October, when higher nutrient availability was observed. Different nitrite reducer groups prevailed in spring and autumn. While nirS, followed by nosZ and nirK, was most abundant in March, the latter was the dominant nitrite reductase in October.