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Marine Ecology Progress Series

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MEPS 552:81-92 (2016)  -  DOI:

Nitrogen response of natural phytoplankton communities: a new indicator based on photosynthetic efficiency Fv/Fm

Emily Ann Saeck1,*, Katherine Rosemary O’Brien2, Michele Astrid Burford1

1Australian Rivers Institute, Griffith University, 170 Kessels Road, Nathan, Queensland 4111, Australia
2School of Chemical Engineering, The University of Queensland, Brisbane, Queensland 4072, Australia
*Corresponding author:

ABSTRACT: The availability of the primary limiting nutrient plays a major role in driving the productivity, biomass and community composition of coastal phytoplankton, but there is an ongoing challenge to define the relationship between nutrient enrichment and phytoplankton response. This study explored a new indicator (N95) for quantifying nutrient response in natural phytoplankton communities. In this study, N95 specifically represented the required nitrogen addition (normalised to chlorophyll a) for the sampled phytoplankton population to reach 95% of nitrogen-replete photosynthetic efficiency. To calculate N95, an asymptotic model was applied to measures of phytoplankton photosynthetic efficiency (Fv/Fm) taken after 24 h incubations under a range of nitrogen enrichment treatments. Applying the method in an Australian subtropical bay, Moreton Bay, nitrogen response was lowest nearshore and high, yet variable, offshore. This pattern reflected the ambient nutrient gradient of declining concentrations with distance offshore. A Moreton Bay-specific threshold in phytoplankton nutrient response was identified at the ambient dissolved inorganic nitrogen concentration of 2 µmol l-1, above which the response to nitrogen enrichment did not increase for 82% of samples. Advantages to measuring N95 were that incubations were simple to set up, incubation period was short, and Fv/Fm measures were simple to make. This approach advances options for using Fv/Fm measures to assess phytoplankton nutrient response and provides a new and sensitive biological indicator applicable to long-term water quality monitoring programs, relevant to parameterising ecological models and supporting decision making on nutrient management.

KEY WORDS: Microalgae · Microbial · Eutrophication · Bioassay · PHYTO-PAM · Fluorescence · Maximum quantum yield of PSII

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Cite this article as: Saeck EA, O’Brien KR, Burford MA (2016) Nitrogen response of natural phytoplankton communities: a new indicator based on photosynthetic efficiency Fv/Fm. Mar Ecol Prog Ser 552:81-92.

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