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Nutrient recycling by Daphnia reduces N 2 fixation by cyanobacteria
Author(s) -
MacKay Neil A.,
Elser James J.
Publication year - 1998
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.1998.43.2.0347
Subject(s) - daphnia , nutrient , cyanobacteria , biology , cladocera , phytoplankton , branchiopoda , incubation , zoology , algae , water column , carbon fixation , zooplankton , environmental chemistry , daphnia magna , phosphorus , botany , ecology , carbon dioxide , chemistry , toxicity , biochemistry , bacteria , genetics , organic chemistry
A field experiment in an experimentally eutrophied lake (Lake 227) tested the hypothesis that differential recycling of nitrogen and phosphorus by Daphnia (a zooplankter with low body N:P ratio) affects the physiological status of cyanobacteria, including rates of N 2 fixation (stoichiometric recycling hypothesis). After a 5‐d incubation in 2.4‐liter bottles, Daphnia treatments had lower standing stocks of algae (based on particulate carbon or Chl a ) and higher concentrations of dissolved nutrients than did Epischura (a high N:P ratio consumer) or control treatments lacking macrozooplankton. The N:P ratio of dissolved nutrients was higher in the Daphnia treatments than in control or Epischura treatments, consistent with the stoichiometric recycling hypothesis, and was associated with greater algal P deficiency. Measurements of absolute and C‐specific N 2 fixation rates following the incubation showed that Daphnia treatments experienced a 50% reduction in N 2 fixation relative to Epischura and control treatments. This reduction is consistent with the higher N:P ratio of the dissolved pool in the Daphnia treatment, as N 4 ‐N inhibits N 2 fixation. Thus, by differentially recycling N 4 ‐N relative to P, Daphnia reduce the advantage (N 2 fixation) cyanobacteria have~over other phytoplankton. We suggest that this mechanism may be an important factor in the ability of Daphnia to reduce the incidence of cyanobactetial blooms in lakes with low N:P loading ratios.