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Interactions between changing pCO2, N2 fixation, and Fe limitation in the marine unicellular cyanobacterium Crocosphaera
Author(s) -
Fu Fei-Xue,
Mulholland Margaret R.,
Garcia Nathan S.,
Beck Aaron,
Bernhardt Peter W.,
Warner Mark E.,
Sañudo-Wilhelmy Sergio A.,
Hutchins David A.
Publication year - 2008
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.2008.53.6.2472
Subject(s) - carbon fixation , biogeochemical cycle , photosynthesis , environmental chemistry , nitrogen fixation , glacial period , cyanobacteria , carbon dioxide , nitrogen , chemistry , botany , biology , ecology , organic chemistry , bacteria , paleontology , genetics
We examined the physiological responses of steady‐state iron (Fe)‐replete and Fe‐limited cultures of the biogeochemically critical marine unicellular diazotrophic cyanobacterium Crocosphaera at glacial (19 Pa; 190 ppm), current (39 Pa; 380 ppm), and projected year 2100 (76 Pa; 750 ppm) CO 2 levels. Rates of N 2 and CO 2 fixation and growth increased in step with increasing partial pressure of CO 2 (pCO 2 ), but only under Fe‐replete conditions. N 2 and carbon fixation rates at 75 Pa CO 2 were 1.4‐1.8‐fold and 1.2‐2.0‐fold higher, respectively, relative to those at present day and glacial pCO 2 levels. In Fe‐replete cultures, cellular Fe and molybdenum quotas varied threefold and were linearly related to N 2 fixation rates and to external pCO 2 . However, N 2 fixation and trace metal quotas were decoupled from pCO 2 in Fe‐limited Crocosphaera . Higher CO 2 and Fe concentrations both resulted in increased cellular pigment contents and affected photosynthesis vs. irradiance parameters. If these results also apply to natural Crocosphaera populations, anthropogenic CO 2 enrichment could substantially increase global oceanic N 2 and CO 2 fixation, but this effect may be tempered by Fe availability. Possible biogeochemical consequences may include elevated inputs of new nitrogen to the ocean and increased potential for Fe and/or phosphorus limitation in the future high‐CO 2 ocean, and feedbacks to atmospheric pCO 2 in both the near future and over glacial to interglacial timescales.