DNRA in intertidal sediments of the Yangtze Estuary

Abstract

Dissimilatory nitrate reduction to ammonium (DNRA) plays an important role in regulating the fate of reactive nitrogen in estuarine and coastal ecosystems. In this work, intertidal sediments of the Yangtze Estuary were collected in January and August 2015. Potential rates of DNRA and associated functional gene were investigated with nitrogen isotope‐tracing and molecular techniques. The measured DNRA rates ranged from 0.14 to 5.57 μmol 15N kg−1 h−1 in the intertidal sediments. DNRA rates were tightly related to abundance of nrfA gene (p < 0.001), demonstrating that fermentation reaction may be the dominant pathway of DNRA in the study area. Redundancy analysis (RDA) showed a relationship between DNRA and organic matter and NO2−, suggesting that these substrates stimulated the metabolism of DNRA microorganisms. On the other hand, the correlation between abundances of nrfA gene and Fe2+ and sulfide in the RDA analysis implied that oxidation of both Fe2+ and sulfide can enhance fermentative DNRA by providing extra free energy. DNRA converted approximately 2.29 × 105 t of nitrate to ammonia annually in the sampling area of the Yangtze Estuary, and most of the converted ammonium was retained in the estuarine ecosystem. DNRA may further contribute to eutrophication in the Yangtze Estuary and also in the other hypereutrophic estuaries.

Reviews and syntheses: Processes and functional genes involved in nitrogen cycling in marine environments

“…For this reason, DNRA may be energetically favored over denitrification in C-rich 5 anoxic environments where NO 3 − is limiting and electron donors (organic C or S -2 ) are in excess (Kraft et al, 2014;Tiedje, 1988). It has been suggested that DNRA is regulated by O 2 and is not affected by NO 2 − (van den Berg et al, 2017), which contrasts with reports of DNRA rates being stimulated by NO 2 − in estuaries (Yin et al, 2017). It is also assumed that DNRA is not affected by NH 4 + (Papaspyrou et al, 2014;Tiedje, 1988), but it has been demonstrated that NH 4 + concentration is positively correlated with DNRA rates (Lisa et al, 2015;Song et al, 2014).…”

“…The abundance of nrfA genes is correlated with S -2 and Fe 2+ , which can enhance DNRA by providing extra free energy (Robertson et al, 2016;Yin et al, 2017). Elevated temperatures increase DNRA rates; therefore, DNRA may be an important pathway for NO 3 − conversion during summer (Yin et al, 2017).…”

“…In the Jiaojiang estuary, organic content seems to be the most important factor affecting the 5 distribution of n-damo communities, NC10 bacteria being more abundant in the intertidal than in the subtidal sediments (Lidong et al, 2014). In addition, the activity of NC10 bacteria varies seasonally and spatially in the coastal sediments of the East China Sea, being higher in the spring and lower in the intertidal zone (Wang et al, 2017). The structure of this community in coastal sediments seems to be highly influenced by NO 3 − concentrations (Wang et al, 2017), as well as by NH 4 + and NO 2 − (Chen et al, 2015).…”

“…Elevated temperatures increase DNRA rates; therefore, DNRA may be an important pathway for NO 3 − conversion during summer (Yin et al, 2017). In coastal zones, this process can also be affected 15…”

Influence of nitrate and nitrite concentration on N2O production via dissimilatory nitrate/nitrite reduction to ammonium in Bacillus paralicheniformis LMG 6934

“…ammonification, dissimilatory nitrate/nitrite reduction to ammonium, nitrate respiration, nitrogen assimilation surveys (Bu et al, 2017;Silver, Herman, & Firestone, 2001;Silver, Thompson, Reich, Ewel, & Firestone, 2005;Song, Lisa, & Tobias, 2014;Yin et al, 2017) and research with pure cultures (Bleakley & Tiedje, 1982;Mania, Heylen, Spanning, & Frostegård, 2014;Smith & Zimmerman, 1981;Stremińska, Felgate, Rowley, Richardson, & Baggs, 2012;Sun, De Vos, & Heylen, 2016) have suggested that NO 3 − -ammonifying bacteria could be a significant source of N 2 O.…”