Original Article

The ISME Journal (2016) 10, 2184–2197; doi:10.1038/ismej.2016.18; published online 26 February 2016

Nitrification and its influence on biogeochemical cycles from the equatorial Pacific to the Arctic Ocean
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Takuhei Shiozaki1, Minoru Ijichi1, Kazuo Isobe2, Fuminori Hashihama3, Ken-ichi Nakamura4, Makoto Ehama3, Ken-ichi Hayashizaki5, Kazutaka Takahashi4, Koji Hamasaki1 and Ken Furuya4

  1. 1Department of Marine Ecosystem Dynamics, Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba, Japan
  2. 2Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
  3. 3Department of Ocean Sciences, Tokyo University of Marine Science and Technology, Tokyo, Japan
  4. 4Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
  5. 5School of Marine Biosciences, Kitasato University, Kanagawa, Japan

Correspondence: Current address: T Shiozaki, Research and Development Center for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15, Natsushima, Yokosuka, Kanagawa 237-0061, Japan. E-mail: takuhei.shiozaki@jamstec.go.jp

Received 21 August 2015; Revised 3 January 2016; Accepted 5 January 2016
Advance online publication 26 February 2016

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Abstract

We examined nitrification in the euphotic zone, its impact on the nitrogen cycles, and the controlling factors along a 7500km transect from the equatorial Pacific Ocean to the Arctic Ocean. Ammonia oxidation occurred in the euphotic zone at most of the stations. The gene and transcript abundances for ammonia oxidation indicated that the shallow clade archaea were the major ammonia oxidizers throughout the study regions. Ammonia oxidation accounted for up to 87.4% (average 55.6%) of the rate of nitrate assimilation in the subtropical oligotrophic region. However, in the shallow Bering and Chukchi sea shelves (bottom less than or equal to67m), the percentage was small (0–4.74%) because ammonia oxidation and the abundance of ammonia oxidizers were low, the light environment being one possible explanation for the low activity. With the exception of the shallow bottom stations, depth-integrated ammonia oxidation was positively correlated with depth-integrated primary production. Ammonia oxidation was low in the high-nutrient low-chlorophyll subarctic region and high in the Bering Sea Green Belt, and primary production in both was influenced by micronutrient supply. An ammonium kinetics experiment demonstrated that ammonia oxidation did not increase significantly with the addition of 31–1560nm ammonium at most stations except in the Bering Sea Green Belt. Thus, the relationship between ammonia oxidation and primary production does not simply indicate that ammonia oxidation increased with ammonium supply through decomposition of organic matter produced by primary production but that ammonia oxidation might also be controlled by micronutrient availability as with primary production.