DNRA dominates over denitrification during algal blooms in a mesotrophic lake: Implications for nitrogen retention
Chen Wang1, Jian Shen2, Huaji Liu2
1School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China; National Observation and Research Station of Erhai Lake Ecosystem in Yunnan, Dali, 671000, China; Yunnan Dali Research Institute of Shanghai Jiao Tong University, Dali, 671000, China; School of Engineering, Dali University, Dali, 671003, China.
Abstract:
Nitrogen (N) overloading threatens global lake ecosystems. However, how algal blooms affect the N balance in mesotrophic lakes by shaping N-cycling biogeographic patterns remains a critical knowledge gap. This study systematically elucidated N cycling patterns and microbial mechanisms driving N retention during algal blooms in Erhai Lake by integrating field monitoring,15N isotope pairing technique (15N-IPT), and absolute quantitative metagenomics. Results revealed that algal blooms shaped a N-cycling functional pattern in Erhai Lake characterized by organic degradation and synthesis (ODAS) dominance and dissimilatory nitrate reduction (DNR) as a key process. Notably, algal blooms disrupted traditional nitrification-denitrification coupling, shifting N cycling towards a retention mode dominated by dissimilatory nitrate reduction to ammonium (DNRA). Sedimentary DNRA contributed 69% (14.69 ± 5.57 μmol N L-1 h-1) of total dissimilatory nitrate reduction (DNR) process, supported by significantly elevated NrfA (602.49 ± 121.04 μmol d-1 g-1) and NirBD (361.29 ± 138.39 μmol d-1 g-1) enzyme activities. Partial Least Squares Path Modeling (PLS-PM) identified the nitrogen retention index (NRI) as co-regulated by water depth and algal-mediated microbial activity/rates. High-NRI sediments were dominated by Bacteroidota (mainly orders Marinilabiliales and families Prolixibacteraceae) and Myxococcota (primarily families Anaeromyxobacteraceae), while low-NRI sediments were characterized by enrichment of Pseudomonadota (Thioalkalivibrio nitratireducens and Gallionellaceae) and Campylobacterota (Campylobacter sp. BCW_8712). DNRA outcompeted denitrification, diverting nitrate to ammonium rather than N2 gas and resulting in an internal N loading that was an order of magnitude higher than external inputs. This work challenges the denitrification-centric paradigm, revealing the microbial mechanisms of endogenous N accumulation under algal bloom conditions and providing a theoretical basis for the management of plateau lakes.
Related Concept Videos
Inorganic Nitrogen Assimilation
Metabolism of Chemolithotrophs
Overview of Nitrogen Metabolism
The largest pool of nitrogen available in the terrestrial ecosystem is gaseous nitrogen (N2) from the air, but this...
Freshwater Microbial Ecology
1° Amines to Diazonium or Aryldiazonium Salts: Diazotization with NaNO2 Overview
The nitrous acid is unstable. Hence, it is formed in situ from a solution of sodium nitrite and cold aqueous acids such as hydrochloric or sulfuric acid. In an acidic solution, the –OH group of nitrous acid undergoes protonation to give oxonium ion, followed by...
1° Amines to Diazonium or Aryldiazonium Salts: Diazotization with NaNO2 Mechanism


