Purpose

The recently identified nosZII gene plays a key role in mitigating nitrous oxide (N₂O) emissions, and emergent macrophytes along lakeshores are areas of significant N₂O emissions. The rhizosphere microenvironments of emergent macrophytes provide habitats that can potentially influence the abundance and composition of nosZII-containing microorganisms and, therefore, N₂O emissions.

Methods

Here we compared the N₂O/(N₂O+N₂) ratio between the rhizospheres of Phragmites australis and bulk sediments from lakes situated in the middle and lower reaches of the Yangtze River plain (YR) and Yunnan-Kweichow plateau (YK) in China. The abundance and composition of nosZII-containing members were investigated using the real-time quantitative PCR and high-throughput sequencing techniques. We also investigated the effects of sediment properties and denitrifying microbial communities on the N₂O/(N₂O+N₂) ratio through path analysis.

Results

The rhizospheres of Phragmites australis maintained significantly higher potential denitrification rates, higher denitrifier abundance, and higher diversity of N₂O-reducing microbial community, but lower N₂O/(N₂O+N₂) ratio at the YR site (P < 0.05). The N₂O/(N₂O+N₂) ratio at the YR site was mainly influenced by N nutrients and the abundance of nirK, nirS, and nosZII genes, whereas the sediment organic matter, and the abundance of nirK, nirS, and nosZI genes were strong predictors of the N₂O/(N₂O+N₂) ratio at the YK site.

Conclusion

This study revealed variable effects of Phragmites australis on altering the nosZII community composition and mitigating N₂O emissions between different regions, which would provide useful information for reducing N₂O emissions from the aquatic ecosystem.