Reduced nitrite accumulation at the primary nitrite maximum in the cyclonic eddies in the western North Pacific subtropical gyre

Liu, Li; Chen, Mingming; Wan, Xiaoliang; Du, Chuanjun; Liu, Zhiyu; Hu, Zhendong; Jiang, Zhiping; Zhou, Kuanbo; Lin, Hongyang; Shen, Hui; Zhao, Duo; Yuan, Limei; Hou, Lei; Yang, Jinqiu; Li, Xiaolin; Kao, Shuh‐Ji; Zakem, Emily; Qin, Wei; Dai, Minhan; Zhang, Yao

doi:10.1126/sciadv.ade2078

Cited by 11 publications

(5 citation statements)

References 64 publications

(101 reference statements)

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“…To minimize the potential enhancement of the in-situ rates due to enrichment by tracer concentrations, the final concentrations of 15 N-NH4 + , 15 N-urea and 15 N-NO2were limited to 20 nmol L -1 . The final concentrations of NH4 + , urea and NO2in our incubations were close to or lower than the Ks measured in our study and the reported values for ammonia oxidation, urea oxidation and nitrite oxidation rates measured in the wNPSG and the NWP (Liu et al, 2023;Xu et al, 2019), suggesting an overall substrate limiting condition in our incubations. Therefore, we applied a linear regression approach using equations (1-2), with the following assumptions, to obtain the estimates of the in-situ reaction rates (Wan et al, 2018).…”

Section: Rate Calculationsupporting

confidence: 87%

“…For depths that exhibited typical M-M type kinetic response, the Ks of ammonia oxidation and nitrite oxidation varied between 24-390 nmol L -1 , and 61-225 nmol L -1 , falling in the range of reported Ks in the open ocean systems (e.g., Liu et al, 2023;Mdutyana et al, 2022;Wan et al, 2018). For urea oxidation, the Ks varied in the range 97-263 nmol N L -1 , which was higher than the Ks for NH4 + at the corresponding depths, suggesting a higher affinity towards NH4 + in marine AOA.…”

Section: Kinetic Traits Determine Marine Nh4 + Urea and No2distributionmentioning

confidence: 77%

“…respectively. The data sources are from the Sothern Ocean (SO) (Mdutyana et al, 2022a, b), the Eastern Tropical North Pacific (ETNP) (Frey et al, 2022;Sun et al, 2017), Eastern Tropical South Pacific (ETSP) (Peng et al, 2016), the Hood Canal (Horak et al, 2013), BATs (Newell et al, 2013), the South China Sea (SCS) (Wan et al, 2018;Zhang et al, 2020), the Northwestern Pacific (NWP) (Xu et al, 2019), the North Pacific Subtropical Gyre (NPSG) (Liu et al, 2023), and the results from this study.…”

Section: Discussionmentioning

confidence: 99%

“…We further added our results to a recently compiled dataset (Liu et al, 2023) to investigate the spatial distribution of the Ks in the ocean. The results exhibited a power law profile of Ks for ammonia oxidation and nitrite oxidation as a function of water depth, although some data points measured in the mesopelagic zone of the SCS and the NWP stations were higher than the fitted values (Fig.…”

Section: Kinetic Traits Determine Marine Nh4 + Urea and No2distributionmentioning

confidence: 99%

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Significance of urea oxidation to nitrite production in the oligotrophic ocean

Wan,

Sheng

et al. 2024

Preprint

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Nitrification, the stepwise oxidization of ammonia to nitrate via nitrite, is a key process in the marine nitrogen cycle. Reported nitrite oxidation rates frequently exceed ammonia oxidation rates below the euphotic zone, raising the fundamental question of whether the two steps are balanced and if alternative sources contribute to nitrite production in the dark ocean. Here we present vertically resolved profiles of ammonia, urea, and nitrite oxidation rates and their kinetic traits extending from the South China Sea to the western North Pacific Subtropical Gyre. Our resultsshow active urea oxidation in the presence of experimental ammonium amendment, indicating direct urea oxidation. Urea oxidation rate covaries with ammonia oxidation rate, and the depthintegrated rates of urea oxidation and ammonia oxidation are comparable, demonstrating urea oxidation is a significant source of nitrite that helps to balance the two steps of nitrification in the oligotrophic ocean. Nitrifiers exhibit high affinity for their substrates, and the apparent halfsaturation constants for ammonia and nitrite oxidation decreased with depth. The apparent halfsaturation constant for urea oxidation is 1.2 to 11-fold (median 2.2) higher than that for ammonia oxidation at the corresponding depths, but with no clear vertical trend. Such kinetic traits may account for the relatively higher urea concentration compared to ammonium and nitrite concentrations in the ocean's interior. Moreover, combining our results with a review of the previous literature shows a trend of increased urea oxidation relative to ammonia oxidation, from the more eutrophic coastal zone to the oligotrophic open ocean, revealing a substrate-dependent biogeographic distribution of urea oxidation across marine environments.

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Section: Rate Calculationsupporting

confidence: 87%

Section: Kinetic Traits Determine Marine Nh4 + Urea and No2distributionmentioning

confidence: 77%

Section: Discussionmentioning

confidence: 99%

Section: Kinetic Traits Determine Marine Nh4 + Urea and No2distributionmentioning

confidence: 99%

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Significance of urea oxidation to nitrite production in the oligotrophic ocean

Wan,

Sheng

et al. 2024

Preprint

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“…Our results indicated that the growth rates of AO could approach those of pure cultures growing under NH 4 + ‐replete conditions and in the absence of grazing control. However, a recent study has shown that the half‐saturation constants of NH 4 + oxidation in the deep euphotic zone of the North Pacific can be no more than 10 nmol L −1 (Liu et al., 2023). The implication is that even ambient NH 4 + concentrations may be near saturated concentrations.…”

Section: Discussionmentioning

confidence: 99%

Top‐Down Control of Ammonia Oxidizers by Grazing in the North Pacific

Ni,

Xu,

et al. 2024

Geophysical Research Letters

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The impact of grazing pressure on ammonia oxidizers (AO) has never been quantified in the field. Here we develop a new method to quantify the grazing rates on AO in aquatic systems. We introduce 15NH4+ tracer into the traditional dilution experiments to measure AO's apparent growth rates by using the end‐product of 15NH4+ oxidation, that is, 15NOx−. Field studies in the North Pacific revealed that 15NOx− in the end‐product was sensitive enough to detect AO's grazing rates. Experiments from the lower euphotic zone showed NH4+ replete growth rates of 0.40 d−1 and 0.77 d−1 of AO and in situ grazing rates on AO of 0.41 d−1 and 0.45 d−1, respectively, indicating a strong top‐down control by grazing on AO. Compiled data show a vertical decoupling between ammonia oxidation rates and AO abundance within the euphotic zone, indicating that strong grazing may have affected the distribution of AO in the global ocean.

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Determination of site‐specific nitrogen cycle reaction kinetics allows accurate simulation of in situ nitrogen transformation rates in a large North American estuary

Tang,

Fortin,

Intrator

et al. 2024

Limnology & Oceanography

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Nitrogen (N) bioavailability affects phytoplankton growth and primary production in the aquatic environment. N bioavailability is partly determined by biological N cycling processes that either transform N species or remove fixed N. Reliable estimates of their kinetic parameters can help understand the distribution of N cycling processes. However, available estimates of kinetic parameters are often derived from microbial isolates and may not be representative of the natural environment. Observations are particularly lacking in estuarine and coastal waters. We conducted isotope tracer addition incubations to evaluate substrate affinities of nitrification, denitrification and anammox in the Chesapeake Bay water column. The half‐saturation constant for ammonia oxidation ranged from 0.38 to 0.75 μM ammonium, substantially higher than observed in the open oceans. Half‐saturation constants for denitrification—0.92–1.86 μM nitrite or 1.15 μM nitrate—were within the lower end or less than those reported for other aquatic environments and for denitrifier isolates. Interestingly, water column denitrification potential was comparable to that of sedimentary denitrification, highlighting the contribution of the water column to N removal during anoxia. Mostly undetectable anammox rates prevented us from deriving the half‐saturation constants, suggesting a low affinity of anammox. Using these substrate kinetics, we were able to predict in situ N cycling rates and explain the vertical distribution of N nutrient concentrations. Our newly derived substrate kinetics parameters can be useful for improving model representation of N nutrient dynamics in estuarine and coastal waters, which is critical for assessing the ecosystem productivity and function.

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Reduced nitrite accumulation at the primary nitrite maximum in the cyclonic eddies in the western North Pacific subtropical gyre

Cited by 11 publications

References 64 publications

Significance of urea oxidation to nitrite production in the oligotrophic ocean

Significance of urea oxidation to nitrite production in the oligotrophic ocean

Top‐Down Control of Ammonia Oxidizers by Grazing in the North Pacific

Determination of site‐specific nitrogen cycle reaction kinetics allows accurate simulation of in situ nitrogen transformation rates in a large North American estuary

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