Aquatic Sciences Meeting, Albuquerque 2001

PC13 Phytoplankton: Trace Metals and Biochemistry

Date: Thursday, February 15, 2001

Location: Southwest Hall

Marino, R, , Cornell University, Ithaca, USA, rmm3@cornell.edu

Howarth, R, W, Environmental Defense/Marine Biological Laboratory, Woods Hole, USA, bhowarth@environmentaldefense.org

Cole, J, J, Institute of Ecosystem Studies, Millbrook, USA, ColeJ@ecostudies.org

Chan, F, , Cornell University, Ithaca , USA, fc19@cornell.edu

THE EFFECT OF SULFATE ON MO-DEPENDENT NITROGEN FIXATION BY HETEROCYSTIC CYANOBACTERIA UNDER SEAWATER CONDITIONS

We examined the interacting effect of sulfate with molybdate at freshwater and seawater concentrations on planktonic nitrogen fixation in a microcosm experiment using a natural population of heterocystic cyanobacteria . A strong inhibition of N fixation by sulfate under seawater conditions was found, with only a small reversal at higher Mo. This was counter to our expectations based on previous formulations characterizing the sulfate effect on Mo assimilation as competitive inhibition of a single uptake system, but was consistent with a larger scale seawater experiment. A re-examination of published kinetic data suggests that Mo transport in planktonic algae and cyanobacteria is not best described by a single system, competitive inhibition model. We hypothesize that both sulfate and molybdate concentrations and relative proportions determine the availability of Mo in a way that likely involves multiple uptake systems and is finely tuned to environmental conditions. This interpretation affects the degree of constraint sulfate imposes on bloom development and N fixation in low salinity estuarine systems but does not negate the ecological significance of a sulfate-constrained growth rate in comparison with freshwaters.

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Aquatic Sciences Meeting, Albuquerque 2001

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