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Title: Carbon-nitrogen stress, and the growth of marine phytoplankton
Author: Clark, D. R.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1999
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A number of phytoplankton species from a range of taxa (including diatoms, dinoflagellates and prymnesiophytes) were grown in batch cultures in closed systems at four dissolved inorganic carbon concentrations. Cultures were supplied with NO3- or NH4+ and growth was limited by C and/or N. Response of the phytoplantkon to C and/or N stress was investigated with measurements including C:N ratios, cell C, N and chl.a quotas, chl.a:C ratios and the internal amino acid pool. Responses to C-limitation included an increase in cell N and chl.a quota, chl.a:C ration and the gln:glu ratio. Responses to increased N-limitation included an increase in the cell C-quota and C:N ratio, together with decreases in cell-N and chl.a quota, chl.a:C ratio, and the gln:glu ratio. Generally indications of N-stress were greater when the N-source was NO3- rather than NH4+ as demonstrated at the level of the cell C, N and chl.a quotas, and at the level of internal amino acid pool, although none of these indicators were found to be consistent for every species. A study of the kinetics of DIC utilisation revealed that to a greater or lesser extent, the utilisation of NO3- relative to NH4+ consistently resulted in a significant decrease in the carbon specific growth rate of all species investigated. The expression of extracellular carbonic anhydrase may endow marine phytoplankton with a competitive advantage, regardless of cell size or motility, while large and chain forming species appeared to be at a relative disadvantage with respect to the kinetics of DIC utilisation. Typically, the species investigated attained a KG for dissolved inorganic carbon of <300 μM. The results of the study suggest that DIC rate limitation of phytoplankton growth may be of minor consequence in the marine environment.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available