Biological Nitrogen Fixation in Sediments of a Cyanobacterial Bloom-Occurring Bay in One Eutrophic Shallow Lake: Occurrence and Related Environmental Factors

Biological nitrogen fixation (BNF) is an important source of bioavailable nitrogen in the aquatic environment that supports primary production. However, little is known about its occurrence and potential in eutrophic freshwater habitats. This study investigated the diazotrophic diversity and seasonal variation of nitrogenase activity (NA) in the sediments of a cyanobacterial bloom-occurring bay of a freshwater lake. Sequencing analysis of the nifH gene revealed that diazotrophs in Clusters I and III constituted the dominant components of the diazotrophic community in Meiliang Bay. Both nifH and 16S rRNA gene sequencing indicated that the microbes in sediments have different community structures during the winter than during other seasons. The concentrations of dissolved sulfide, sulfate, and nitrate in pore water were significantly correlated with NA in sediments; however, the Mantel test indicated that dissolved sulfide had a more significant effect on the structure of the diazotrophic community than did other environmental factors. Laboratory culture experiments under different redox conditions further confirmed the inhibitory effect of dissolved sulfide on BNF in sediments. This study revealed that the BNF in sediments of Meiliang Bay was closely linked to variations in dissolved sulfide concentration, which has broadened our understanding of BNF in freshwater lakes.

Automated summary

This study revealed that biological nitrogen fixation (BNF) in sediments of Meiliang Bay is closely linked to variations in dissolved sulfide concentration, which has broadened our understanding of BNF in freshwater lakes. The composition of diazotrophic community in sediments varied between seasons, with dissolved sulfide having a more significant effect on the structure of the community.