Denitrification contributes to N2O emission in paddy soils

Hua Xiang; Yiguo Hong; Jiapeng Wu; Yu Wang; Fei Ye; Jiaqi Ye; Jing Lu; Aimin Long

doi:10.3389/fmicb.2023.1218207

Denitrification contributes to N₂O emission in paddy soils

Front Microbiol. 2023 Jun 16:14:1218207. doi: 10.3389/fmicb.2023.1218207. eCollection 2023.

Authors

Hua Xiang^{1

2

3}, Yiguo Hong², Jiapeng Wu², Yu Wang², Fei Ye², Jiaqi Ye², Jing Lu², Aimin Long^{1

3}

Affiliations

¹ State Key Laboratory of Tropical Oceanography (LTO), South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China.
² Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Institute of Environmental Research at Greater Bay Area, Ministry of Education, Guangzhou University, Guangzhou, China.
³ University of Chinese Academy of Sciences, Beijing, China.

Abstract

Denitrification is vital to nitrogen removal and N₂O release in ecosystems; in this regard, paddy soils exhibit strong denitrifying ability. However, the underlying mechanism of N₂O emission from denitrification in paddy soils is yet to be elucidated. In this study, the potential N₂O emission rate, enzymatic activity for N₂O production and reduction, gene abundance, and community composition during denitrification were investigated using the ¹⁵N 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 N₂O emission rates were 0.51 ± 0.20 μmol⋅N⋅kg^-1⋅h^-1, which constituted 2.16 ± 0.85% of the denitrification end-products. The enzymatic activity for N₂O production was 2.77-8.94 times than that for N₂O reduction, indicating an imbalance between N₂O production and reduction. The gene abundance ratio of nir to nosZ 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 norB gene without nosZ genes, including Actinobacteria, Planctomycetes, Desulfobacterota, Cyanobacteria, Acidobacteria, Bacteroidetes, and Myxococcus, may contribute to N₂O 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 N₂O⋅m^-2⋅yr^-1 in surface paddy soils.

Keywords: N2O emission; denitrification; functional gene; microbial taxa; paddy soils.

Grants and funding

This study was funded by the National Natural Science Foundation of China (Nos. 42276130 and 42006122), the Innovation Team Project of Guangdong Provincial Department of Education (No. 2021KCXTD016), and the Basic and Applied Basic Research Foundation for Guangdong Province (Nos. 2019B1515120066, 2020A1515110597, and 2021A1515011548).