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Nitrous oxide (N2O) is a potent greenhouse gas and a major cause of ozone depletion. One-third of atmospheric N2O originates in aquatic environments. Reduction of N2O to dinitrogen gas (N2) requires the nitrous oxide reductase enzyme, which is encoded by the genenosZ. Organisms that containnosZare the only known biological sinks of N2O and are found in diverse genera and a wide range of environments. The two clades ofnosZ(Clade I and II) contain great diversity, making it challenging to study the population structure and distribution ofnosZcontaining organisms in the environment. A database of over 11,000nosZsequences was compiled from NCBI (representing diverse aquatic environments) and unpublished sequences and metagenomes (primarily from oxygen minimum zones, OMZs, where N2O levels are often elevated). Sequences were clustered into archetypes based on DNA and amino acid sequence identity and their clade, phylogeny, and environmental source were determined. Further analysis of the source and environmental distribution of the sequences showed strong habitat separation between clades and phylogeny. Although there are more Clade InosZgenes in the compilation, Clade II is more diverse phylogenetically and has a wider distribution across environmental sources. On the other hand, Clade InosZgenes are predominately found within marine sediment and are primarily from the phylum Pseudonomonadota. The majority of the sequences analyzed from marine OMZs represented distinct phylotypes between different OMZs showing that thenosZgene displays regional and environmental separation. This study expands the known diversity ofnosZgenes and provides a clearer picture of how the clades and phylogeny ofnosZorganisms are distributed across diverse environments.
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This content will become publicly available on February 20, 2026
Ecological Differentiation Among Nitrous Oxide Reducers Enhances Temperature Effects on Riverine N 2 O Emissions
ABSTRACT Nitrous oxide (N2O) reductase, the sole natural microbial sink for N2O, exists in two microbial clades:nosZI andnosZII. Although previous studies have explored inter‐clade ecological differentiation, the intra‐clade variations and their implications for N2O dynamics remain understudied. This study investigated both inter‐ and intra‐clade ecological differentiation among N2O reducers, the drivers influencing these patterns, and their effects on N2O emissions across continental‐scale river systems. The results showed that bothnosZI andnosZII community turnovers were associated with similar key environmental factors, particularly total phosphorus (TP), but these variables explained a larger proportion of variation in thenosZI community. The influence of mean annual temperature (MAT) on community composition increased for more widespread N2O‐reducing taxa. We identified distinct ecological clusters within each clade of N2O reducers and observed identical ecological clustering patterns across both clades. These clusters were primarily characterized by distinct MAT regimes, coarse sediment texture as well as low TP levels, and high abundance of N2O producers, with MAT‐related clusters constituting predominant proportions. Intra‐clade ecological differentiation was a crucial predictor of N2O flux and reduction efficiency. Although different ecological clusters showed varying or even contrasting associations with N2O dynamics, the shared ecological clusters across clades exhibited similar trends. Low‐MAT clusters in both thenosZI andnosZII communities were negatively correlated with denitrification‐normalized N2O flux and the N2O:(N2O + N2) ratio, whereas high‐MAT clusters showed positive correlations. This contrasting pattern likely stems from low‐MAT clusters being better adapted to eutrophic conditions and their more frequent co‐occurrence with N2O‐producing genes. These findings advance our understanding of the distribution and ecological functions of N2O reducers in natural ecosystems, suggesting that warming rivers may have decreased N2O reduction efficiency and thereby amplify temperature‐driven emissions.
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- Award ID(s):
- 2215300
- PAR ID:
- 10573653
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Global Change Biology
- Volume:
- 31
- Issue:
- 2
- ISSN:
- 1354-1013
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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