Abundance and diversity of diazotrophs in the surface sediments of Kongsfjorden, an Arctic fjord

Diazotrophy in the Arctic environment is poorly understood compared to tropical and subtropical regions. Hence in this study, we report the abundance and diversity of diazotrophs in Arctic fjord sediments and elucidate the role of environmental factors on the distribution of diazotrophs. The study was conducted during the boreal summer in the Kongsfjorden, an Arctic fjord situated in the western coast of Spitsbergen. The abundance of nifH gene was measured through quantitative real-time PCR and the diversity of diazotrophs was assessed by nifH targeted clone library and next generation sequence analysis. Results revealed that the abundance of nifH gene in the surface sediments ranged from 2.3x10(6) to 3.7x10(7) copies g(-1). The delta -proteobacterial diazotrophs (71% of total sequence) were the dominant class observed in this study. Major genera retrieved from the sequence analysis were Desulfovibrionaceae (25% of total sequence), Desulfuromonadaceae (18% of total sequence) and Desulfobacteriaceae (10% of total sequence); these are important diazotrophic iron and sulfur-reducing bacterial clade in the Kongsfjorden sediments. The abundance of nifH gene showed a significant positive correlation TOC/TN ratio (r(2)=0.96, p <= 0.05) and total organic carbon (p <= 0.05) content in the fjord sediments. The higher TOC/TN ratio (4.24-14.5) indicated low nitrogen content organic matter in the fjord sediments through glacier runoff, which enhances the abundance and diversity of nitrogen fixing microorganisms.

Automated summary

This study investigated the abundance and diversity of diazotrophs in Arctic fjord sediments, revealing dominance of δ-proteobacterial diazotrophs and significant correlations with TOC/TN ratio and total organic carbon content. Glacier runoff introducing low nitrogen content organic matter enhances the abundance and diversity of nitrogen-fixing microorganisms in the fjord sediments.