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Inorganic nitrogen assimilation by picoplankton and whole plankton in a coastal ecosystem
Author(s) -
Rodrigues Rubina M. N. V.,
Williams Peter J. le B.
Publication year - 2002
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2002.47.6.1608
Subject(s) - picoplankton , autotroph , phytoplankton , plankton , heterotroph , nitrate , assimilation (phonology) , environmental chemistry , nutrient , primary production , nitrogen assimilation , nitrogen , biology , chlorophyll a , botany , zoology , environmental science , chemistry , ecosystem , ecology , bacteria , linguistics , philosophy , genetics , organic chemistry
NH 4 + and NO 3 − seasonal uptake by the phytoplankton and <2−µm communities were investigated in the Menai Strait using 15N tracer techniques. Based on O 2 ‐determined primary production and DIN metabolism measurements, five phases were defined: (1) prebloom (before April), (2) primary net autotrophic (April and May), (3) net heterotrophic (June), (4) secondary net autotrophic (July and August), and (5) regenerative (remainder of calendar year). The inorganic N nutrition of phytoplankton and <2–µm organisms was NO 3 − −based in spring and NH 4 + ‐based in summer and autumn, reflecting varying ambient concentrations of these nutrients superimposed on a general preference for NH 4 + by both communities. The percent contribution of picoplankton to the total NH 4 + uptake was higher than to nitrate (seasonal averages of 50 ± 14% and 32 ± 24%, respectively). The contribution of the <2–µm size fraction was lowest during both net autotrophic phases (4–13%) and highest during the net heterotrophic, prebloom and regenerative phase (70–84%). A strong correlation between percent NH 4 + and NO 3 − assimilation by the <2–µm size fraction and bacteria abundance between May and July suggests significant bacterial uptake at this time. Bacterial DIN utilization was estimated by correcting uptake rates by the <2−µm fraction, for picophytoplankton presence. During the primary net autotrophic phase, inferred bacterial uptake constituted 13 and 34% of total NO 3 − and NH 4 + uptake, respectively. In the net heterotrophic phase, it amounted to ca. 70% of the total DIN uptake, with no differences between nutrients. Competition between bacteria and phytoplankton for depleted DIN could have contributed to the phytoplankton bloom termination.