TY - JOUR
T1 - Revisiting nitrification in the Eastern Tropical South Pacific
T2 - A focus on controls
AU - Peng, Xuefeng
AU - Fuchsman, Clara A.
AU - Jayakumar, Amal
AU - Warner, Mark J.
AU - Devol, Allan H.
AU - Ward, Bettie
N1 - Funding Information:
This work was supported by National Science Foundation Oceanography (OCE) awards 10-29951 to B.B.W. and A.J. and NSF (OCE) award to A.H.D. 10-29316. We are indebted to CalvinMordy for measuring nutrients, Niels Peter Revsbech for the STOX sensor data, the crew of the R/V Thomas Thompson for general assistance, to Karen Casciotti for providing the NO22 stable isotope standard, to Daniel Sigman for consultation, and Sergey Oleynik for superb technical assistance in the laboratory. The data used in this paper will be deposited on http://www. princeton.edu/nitrogen.
Publisher Copyright:
© 2016. American Geophysical Union. All Rights Reserved.
PY - 2016/3/1
Y1 - 2016/3/1
N2 - Nitrification, the oxidation of ammonium (NH4+) to nitrite (NO2-) and to nitrate (NO3-), is a component of the nitrogen (N) cycle internal to the fixed N pool. In oxygen minimum zones (OMZs), which are hotspots for oceanic fixed N loss, nitrification plays a key role because it directly supplies substrates for denitrification and anaerobic ammonia oxidation (anammox), and may compete for substrates with these same processes. However, the control of oxygen and substrate concentrations on nitrification are not well understood. We performed onboard incubations with 15N-labeled substrates to measure rates of NH4+ and NO2- oxidation in the eastern tropical South Pacific (ETSP). The spatial and depth distributions of NH4+ and NO2- oxidation rates were primarily controlled by NH4+ and NO2- availability, oxygen concentration, and light. In the euphotic zone, nitrification was partially photoinhibited. In the anoxic layer, NH4+ oxidation was negligible or below detection, but high rates of NO2- oxidation were observed. NH4+ oxidation displayed extremely high affinity for both NH4+ and oxygen. The positive linear correlations between NH4+ oxidation rates and in situ NH4+ concentrations and ammonia monooxygenase subunit A (amoA) gene abundances in the upper oxycline indicate that the natural assemblage of ammonia oxidizers responds to in situ NH4+ concentrations or supply by adjusting their population size, which determines the NH4+ oxidation potential. The depth distribution of archaeal and bacterial amoA gene abundances and N2O concentration, along with independently reported simultaneous direct N2O production rate measurements, suggests that AOA were predominantly responsible for NH4+ oxidation, which was a major source of N2O production at oxygen concentrations > 5 μM.
AB - Nitrification, the oxidation of ammonium (NH4+) to nitrite (NO2-) and to nitrate (NO3-), is a component of the nitrogen (N) cycle internal to the fixed N pool. In oxygen minimum zones (OMZs), which are hotspots for oceanic fixed N loss, nitrification plays a key role because it directly supplies substrates for denitrification and anaerobic ammonia oxidation (anammox), and may compete for substrates with these same processes. However, the control of oxygen and substrate concentrations on nitrification are not well understood. We performed onboard incubations with 15N-labeled substrates to measure rates of NH4+ and NO2- oxidation in the eastern tropical South Pacific (ETSP). The spatial and depth distributions of NH4+ and NO2- oxidation rates were primarily controlled by NH4+ and NO2- availability, oxygen concentration, and light. In the euphotic zone, nitrification was partially photoinhibited. In the anoxic layer, NH4+ oxidation was negligible or below detection, but high rates of NO2- oxidation were observed. NH4+ oxidation displayed extremely high affinity for both NH4+ and oxygen. The positive linear correlations between NH4+ oxidation rates and in situ NH4+ concentrations and ammonia monooxygenase subunit A (amoA) gene abundances in the upper oxycline indicate that the natural assemblage of ammonia oxidizers responds to in situ NH4+ concentrations or supply by adjusting their population size, which determines the NH4+ oxidation potential. The depth distribution of archaeal and bacterial amoA gene abundances and N2O concentration, along with independently reported simultaneous direct N2O production rate measurements, suggests that AOA were predominantly responsible for NH4+ oxidation, which was a major source of N2O production at oxygen concentrations > 5 μM.
KW - ammonia oxidation
KW - eastern tropical South Pacific
KW - nitrification
KW - nitrite oxidation
KW - oxycline
KW - oxygen minimum zone
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U2 - 10.1002/2015JC011455
DO - 10.1002/2015JC011455
M3 - Article
AN - SCOPUS:84960392003
SN - 2169-9291
VL - 121
SP - 1667
EP - 1684
JO - Journal of Geophysical Research: Oceans
JF - Journal of Geophysical Research: Oceans
IS - 3
ER -