Intra-annual variation of phytoplankton community responses to factorial N,P, and CO2 enrichment in a temperate mesotrophic lake |
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Authors: | Egor Katkov Étienne Low-Décarie Gregor F Fussmann |
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Institution: | 1. Department of Biology, McGill University, Montreal, QC, Canada;2. School of Biological Sciences, University of Essex, Colchester, UK |
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Abstract: | - Across primary producer communities in different lakes, nitrogen (N) and phosphorus (P) can exhibit many different patterns of limitation. Here, we look at the intra-annual variability of these patterns in a single lake. Furthermore, we investigate whether a third resource, carbon dioxide (CO2) can have significant effects on phytoplankton biomass and community composition.
- We performed five in situ lacustrine mesocosm experiments at different times of the year. In each experiment, we had a factorial design with two levels of N, P and CO2 enrichment (no enrichment or double lake concentrations for N and P and atmospheric (400 ppm) and c. 1,000 ppm for CO2) resulting in a total of eight treatments. Mesocosms of c. 1,600 L were suspended in a temperate, mesotrophic lake (Lac Hertel, Canada). Each experiment lasted 2 weeks and chlorophyll a biomass, coarse chemotaxonomic community composition (measured using fluorometry), and several environmental variables were recorded at a minimum of four time points.
- We found that the limiting, synergistic, and community composition effects of N and P varied between experiments. TN:TP ratios explained, in part, some of this variability, along with insolation and water temperature.
- Despite relatively high levels of CO2 in the control mesocosms, we found a constant synergistic effect of CO2 with N. In combination with the synergistic effect of P with N found in some experiments, this provides support for CO2 as one of the multiple limiting resources in nutrient-enriched systems. This finding could have implications for eutrophic lakes exposed to increasing concentrations of CO2.
- We also found that the effects of CO2 on community composition varied intra-annually. Thus, we conclude that generalised predictions about the effect of CO2 on community composition at a coarse chemotaxonomic scale are unlikely to hold, but predictions specific to season and system are likely to be reliable.
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Keywords: | algae co-limitation freshwater mesocosm seasonality |
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