AUTHOR=Xiang Hua , Hong Yiguo , Wu Jiapeng , Wang Yu , Ye Fei , Ye Jiaqi , Lu Jing , Long Aimin 

TITLE=Denitrification contributes to N2O emission in paddy soils

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1218207

DOI=10.3389/fmicb.2023.1218207

ISSN=1664-302X

ABSTRACT=<p>Denitrification is vital to nitrogen removal and N<sub>2</sub>O release in ecosystems; in this regard, paddy soils exhibit strong denitrifying ability. However, the underlying mechanism of N<sub>2</sub>O emission from denitrification in paddy soils is yet to be elucidated. In this study, the potential N<sub>2</sub>O emission rate, enzymatic activity for N<sub>2</sub>O production and reduction, gene abundance, and community composition during denitrification were investigated using the <sup>15</sup>N isotope tracer technique combined with slurry incubation, enzymatic activity detection, quantitative polymerase chain reaction (qPCR), and metagenomic sequencing. Results of incubation experiments showed that the average potential N<sub>2</sub>O emission rates were 0.51 ± 0.20 μmol⋅N⋅kg<sup>–1</sup>⋅h<sup>–1</sup>, which constituted 2.16 ± 0.85% of the denitrification end-products. The enzymatic activity for N<sub>2</sub>O production was 2.77–8.94 times than that for N<sub>2</sub>O reduction, indicating an imbalance between N<sub>2</sub>O production and reduction. The gene abundance ratio of <italic>nir</italic> to <italic>nos</italic>Z from qPCR results further supported the imbalance. Results of metagenomic analysis showed that, although Proteobacteria was the common phylum for denitrification genes, other dominant community compositions varied for different denitrification genes. Gammaproteobacteria and other phyla containing the <italic>nor</italic>B gene without <italic>nos</italic>Z genes, including Actinobacteria, Planctomycetes, Desulfobacterota, Cyanobacteria, Acidobacteria, Bacteroidetes, and Myxococcus, may contribute to N<sub>2</sub>O emission from paddy soils. Our results suggest that denitrification is highly modular, with different microbial communities collaborating to complete the denitrification process, thus resulting in an emission estimation of 13.67 ± 5.44 g N<sub>2</sub>O⋅m<sup>–2</sup>⋅yr<sup>–1</sup> in surface paddy soils.</p>