Rhizosphere-associated nosZ II microbial community of Phragmites australis and its influence on nitrous oxide emissions in two different regions

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. 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. 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. 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.