Potential contributions of nitrifiers and denitrifiers to nitrous oxide sources and sinks in China's estuarine and coastal areas

Abstract

Abstract. Nitrous oxide (N2O) is an important ozone-depleting greenhouse gas produced and consumed by microbially mediated nitrification and denitrification pathways. Estuaries are intensive N2O emission regions in marine ecosystems. However, the potential contributions of nitrifiers and denitrifiers to N2O sources and sinks in China's estuarine and coastal areas are poorly understood. The abundance and transcription of six key microbial functional genes involved in nitrification and denitrification, as well as the clade II-type nosZ gene-bearing community composition of N2O reducers, were investigated in four estuaries spanning the Chinese coastline. The results showed that the ammonia-oxidizing archaeal amoA genes and transcripts were more dominant in the northern Bohai Sea (BS) and Yangtze River estuaries, which had low nitrogen concentrations, while the denitrifier nirS genes and transcripts were more dominant in the southern Jiulong River (JRE) and Pearl River estuaries, which had high levels of terrestrial nitrogen input. Notably, the nosZ clade II gene was more abundant than the clade I-type throughout the estuaries except for in the JRE and a few sites of the BS, while the opposite transcript distribution pattern was observed in these two estuaries. The gene and transcript distributions were significantly constrained by nitrogen and oxygen concentrations as well as by salinity, temperature, and pH. The nosZ clade II gene-bearing community composition along China's coastline had a high level of diversity and was distinctly different from that in the soil and in marine oxygen-minimum-zone waters. By comparing the gene distribution patterns across the estuaries with the distribution patterns of the N2O concentration and flux, we found that denitrification may principally control the N2O emissions pattern.

Mixed Archaeal Production and Nitrifier Denitrification Dominate N2O Production in the East China Sea: Insights From Isotopocule and Hydroxylamine Analyses

“…Thus, archaeal nitrification and/or the hybrid pathway played an important role in shallow water, similar to previous findings in the upper water of the open ocean and coastal seas (Frame et al, 2016;Ji & Ward, 2017;Trimmer et al, 2016). This finding was also supported by previous studies regarding microbial communities, which showed that AOA is ubiquitous and that the archeal amoA gene outnumbers the bacterial amoA gene in the ECS shelf and Yangtze River estuarine water (Dai et al, 2022;Hu et al, 2013). Overall, neither archeal N 2 O production nor nitrifier denitrification alone could explain the observed isotopic composition in the shallow water; each process was estimated to account for ∼47% (range: 38%-55%) and ∼53% (range: 45%-62%), respectively, of the total produced N 2 O, based on the 95% confidence interval (CI) of the estimated SP value from the SP versus 1/N 2 O plot (Figure 8a).…”

P inputs determine denitrifier abundance explaining dissolved nitrous oxide in reservoirs

“…A previous survey in 17 shallow lakes also found a correlation between the abundance of denitrifiers (i.e., nirS / nirK ) in lake sediments and N 2 O fluxes (Zhou et al 2021). Dai et al (2022) found that archaeal amoA genes and transcripts were more dominant in the coastal and estuarine areas which had low nitrogen concentration, while nirS genes and transcripts dominated in the areas of high nitrogen inputs. Based on the distribution patterns, the authors suggested that denitrification may control N 2 O emissions.…”

Nitrous Oxide Consumption in Oxygenated and Anoxic Estuarine Waters

“…However, we cannot ignore the possibility that Chesapeake Bay indeed has higher nosZ gene abundance compared to marine samples. Using the same clade II primers used here, Dai et al (2022) reported up to 10 4 copies mL −1 of clade II nosZ genes in Chinese estuaries. There are no other data on clade-specific nosZ abundance in aquatic systems with which to compare these results for Chesapeake Bay.…”

“…Briefly, clade I nosZ gene abundance was quantified via qPCR with SYBR Green-based assays using the nosZ1mod-F (5′-WCS YTS TTC MTS GAY AGC CAG-3′) and nosZ1mod-R (5′-ATR TCG ATS ARC TGV KCR TTY TC-3′) primer set (Chee- Sanford et al, 2020). In addition, clade II nosZ gene abundance was quantified using the primer set-nosZ-1I-F forward (5′-CTI GGI CCI YTK CAY AC-3′) and nosZ-1I-RNew reverse (5'-KGC RTA GTG IGG YTC DCC-3'), which was optimized for clade II detection in estuarine samples (Dai et al, 2022). Due to the large diversity of nosZ sequences, these primer sets are still likely to miss some fraction of the nosZ sequences (Chee- Sanford et al, 2020;Ma et al, 2019).…”