Spatially tripartite interactions of denitrifiers in arctic ecosystems: activities, functional groups and soil resources

Soil denitrification is one of the most significant contributors to global nitrous oxide (N2O) emissions, and spatial patterns of denitrifying communities and their functions may reveal the factors that drive denitrification potential and functional consortia. Although denitrifier spatial patterns have been studied extensively in most soil ecosystems, little is known about these processes in arctic soils. This study aimed to unravel the spatial relationships among denitrifier abundance, denitrification potential and soil resources in 279 soil samples collected from three Canadian arctic ecosystems encompassing 7 degrees in latitude and 27 degrees in longitude. The abundance of nirS (106108 copies g-1 dry soil), nirK (103-107 copies g-1 dry soil) and nosZ (106107 copies g-1 dry soil) genes in these soils is in the similar range as non-arctic soil ecosystems. Potential denitrification in Organic Cryosols (1034 ng N2O-N g-1 soil) was 511 times higher than Static/Turbic Cryosols and the overall denitrification potential in Cryosols was also comparable to other ecosystems. We found denitrifier functional groups and potential denitrification were highly spatially dependent within a scale of 5 m. Functional groups and soil resources were significantly (P < 0.01) correlated to potential denitrifier activities and the correlations were stronger in Organic Cryosols. Soil moisture, organic carbon and nitrogen content were the predominant controls with nirK abundance also linked to potential denitrification. This study suggests that the dominant control on arctic ecosystem-level denitrification potential is moisture and organic carbon. Further, microbial abundance controls on ecosystem level activity while undoubtedly present, are masked in the nutrient-poor arctic environment by soil resource control on denitrifier ecosystem level activity.