Spatial and Temporal Variability of Microbial Nitrogen Cycling Genes in Arctic Streams

The Arctic is undergoing rapid climate change, with thawing permafrost and shifts in vegetation altering nitrogen (N) delivery into streams. These changes can significantly affect microbial biofilm diversity and functional roles, yet knowledge of streambed microbial biofilms remains scarce across the Arctic. This study examines the biogeographic and temporal patterns of prokaryotic sediment diversity and N functional genes across a biogeographical gradient in Arctic regions. We sampled sediment from 27 streams across four Arctic regions, including 14 streams in Greenland that were sampled at three timepoints throughout the open-water; all other streams were sampled once in midsummer. We analyzed 16S rRNA gene sequencing and quantified six genes involved in the N-fixation (nifH), nitrification (amoA, nxrB), and denitrification (nirS, norB and nosZ). Our results showed that prokaryotic and N functional gene abundances varied among regions, with higher abundance in areas with more catchment vegetation and higher organic matter availability. However, the composition of prokaryote communities and N functional genes showed no regional differences. Prokaryotic abundance and diversity tended to increase toward late summer. This study highlights how catchment properties, particularly organic matter and vegetation, influence stream prokaryotic communities and their role in N cycling, providing key insights into ecosystem responses to climate change in the Arctic.