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Stoichiometry of nitrogen and carbon utilization in cultured populations of Trichodesmium IMS101: Implications for growth
Author(s) -
Mulholland Margaret R.,
Capone Douglas G.
Publication year - 2001
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.2001.46.2.0436
Subject(s) - trichodesmium , nitrogen fixation , nitrogen , ammonium , carbon fixation , zoology , biology , fixation (population genetics) , exponential growth , growth rate , botany , chemistry , photosynthesis , biochemistry , diazotroph , mathematics , mathematical analysis , geometry , organic chemistry , gene
Rates of particulate organic carbon (POC) and particulate organic nitrogen (PON) accumulation, N 2 and CO 2 fixation, and NH 4 + uptake were measured in cultures of Trichodesmium IMS101 growing on an artificial culture medium without added N substrates. Cultures exhibited a doubling time of about 4 d based on the accumulation of PON, POC, chlorophyll a, and cell number. Cell‐specific rates of N 2 and CO 2 fixation were highest during midday and during the initial stages of the growth cycle. Up to midlog phase, integrated estimates of CO 2 fixation (based on short‐term 13 CO 2 uptake) closely tracked increases in POC. However, after day 8, estimates of C accumulation based on CO 2 fixation exceeded observed POC increases. Within the error of the measurements, N 2 fixation estimates (based on C 2 H 2 reduction) also closely tracked, and could largely account for, PON increases over most of the experiment. N demand based on CO 2 fixation also followed PON increases during early to midlog phase but diverged during late exponential phase and thereafter by greater than 100%. Estimates of short‐term C fixation rates during and after late exponential phase overestimate net growth of Trichodesmium IMS101, whereas estimates of N 2 fixation rates approximated net growth. These observations may partially explain the disparity of estimates of growth in field populations based on 14 CO 2 fixation compared to N 2 fixation. Ammonium accumulated in the culture medium during the experiment, and rates of NH 4 + uptake were high throughout the day and over the whole growth cycle. Rates of NH 4 + uptake generally exceeded N 2 fixation. The turnover of N was therefore much greater than the net accumulation of N in biomass and implies a concurrent high rate of NH 4 + release.