Effects of temperature elevation and glucose addition on prokaryotic production and respiration in the mesopelagic layer of the western North Pacific
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Incubation experiments were conducted to determine whether, and to what extent, heterotrophic prokaryotic production (HPP), prokaryotic respiration (PR), and prokaryotic growth efficiency (PGE) vary in response to the addition of dissolved organic carbon (DOC; glucose at a final concentration of 0.5 µmol C L−1) and elevation of water temperature (+5 °C) in the upper mesopelagic layer of the subarctic and subtropical western North Pacific. The addition of DOC or temperature elevation generally enhanced HPP and PR. Synergistic effects of water temperature and DOC were also found, suggesting that prokaryotic consumption of DOC in the mesopelagic layer is partly regulated by water temperature. Despite the large variability in HPP and PR, PGE varied only moderately, yielding an average value of 0.066 (standard deviation = 0.027, n = 8).
KeywordsDissolved organic carbon Mesopelagic layer Prokaryotic growth efficiency Prokaryotic production Prokaryotic respiration Seawater temperature
We are grateful to the captain and crew of the R/V ‘Mirai’, and the staff of Global Ocean Development Inc. and Marine Works Japan Inc. for their support during the cruises. We also thank M. Honda for his coordination of the cruises and H. Fukuda for his assistance with the laboratory analyses on land. This study was financially supported by a Japan Society for the Promotion of Science Grant (JSPS KAKENHI 24241003) awarded to TN. Financial support was also provided by the JSPS Research Fellowship for Young Scientists awarded to MU. We appreciate the constructive comments provided by the Editor and two anonymous reviewers.
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