Interactive effects of nitrogen and phosphorus on growth and stoichiometry of lake phytoplankton

While universal responses to nutrient enrichment is often assumed, the effect size of phytoplankton responses to an increased supply of one nutrient can vary with the availability of the other. Here, we used two complementary two-way factorial experiments to determine how responses of lake phytoplankton to increased N and P supply vary with increasing concentrations of the other nutrient. We manipulated dissolved N and P concentrations in a four-day bioassay conducted with lake phytoplankton and measured chlorophyll-a and carbon (C) specific growth rates, phytoplankton size-classes, chlorophyll-specific N and P removal, and seston C:N:P ratios. These data were used to assess the presence and type of interactive effects between N and P on phytoplankton responses. For most response variables, the effects of increased N supply depended on the background concentration of P and vice versa. The specific nature of effects differed among response variables and depended on the N and P concentrations during the bioassay. Generally, increases of N or P alone elicited few and weaker effects than increased supplies of one element in combination with the other. Overall, our results show that phytoplankton responses to increases in N or P supply are context dependent and likely reflect multiple processes involved in phytoplankton nutrient uptake and use. These results also show that phytoplankton responses to N and P supply ratios can depend on the supply rates of the nutrients, which complicates understanding how single nutrient enrichment affects primary producers in pelagic ecosystems. 

Presentation Preference: Oral

Primary Presenter: Paul Frost, Trent University (paulfrost@trentu.ca)

Authors:

Paul Frost, Department of Biology, Trent University  (paulfrost@trentu.ca)

Nolan Pearce, Department of Biology, Trent University  (nolanpearce@trentu.ca)

Stella Berger, Department of Plankton and Microbial Ecology, Leibniz Institute of Freshwater Ecology and Inland Fisheries  (stella.berger@igb-berlin.de)

Mark Gessner, Department of Plankton and Microbial Ecology, Leibniz Institute of Freshwater Ecology and Inland Fisheries  (mark.gessner@igb-berlin.de)

A. Katharina Makower, Department of Plankton and Microbial Ecology, Leibniz Institute of Freshwater Ecology and Inland Fisherie  (katharina.makower@igb-berlin.de)

Vanessa Marzetz, Zoological Institute and Museum, University of Greifswald  (vanessa.marzetz@web.de)

Jens Nejstgaard, Department of Plankton and Microbial Ecology, Leibniz Institute of Freshwater Ecology and Inland Fisheries  (jens.nejstgaard@igb-berlin.de)

Aljona Pralle, Department of Plankton and Microbial Ecology, Leibniz Institute of Freshwater Ecology and Inland Fisheries  (aljona.pralle@outlook.com)

Svenja Schälicke, Institute for Biochemistry and Biology, University of Potsdam  (svenja.schaelicke@lageso.berlin.de)

Alexander Wacker, Zoological Institute and Museum, University of Greifswald  (alexander.wacker@uni-greifswald.de)

Nicole Wagner, Department of Biological Sciences, Oakland University  (nicolewagner@oakland.edu)

Marguerite Xenopoulos, Department of Biology, Trent University  (mxenopoulos@trentu.ca)