Warming effect in a multiple stressor context: role of thermal variability and resource supply shaping phytoplankton communities’ responses to environmental change
Final Report Abstract
Freshwater ecosystems provide critical ecosystem services but are threatened by human activities causing modifications in temperature and nutrients. Current studies focus mostly on simplified evaluations by either considering changes in temperature mean and variability separately, considering one nutrient concentration but not the balance between multiple nutrients, or are mostly based on single species omitting community interactions. The overall aim of this project was to assess the responses of freshwater natural communities to changes in temperature mean and variance, taking into account interactions with local factors, i.e. the nutrient context and thermal history. We tested how predictions developed using simplified approaches could be scaled up to the community context. First, we evaluated the thermal responses curves for maximum growth rates and maximum biomass in natural phytoplankton communities. We found that community performance and maximum biomass were non-linear functions of temperature shaped by the nutrient supply level as expected by theory, despite community composition adjustments to different conditions. Second, we investigated the effects of increasing temperature mean and variance across a wide range of nutrient scenarios. We showed that increased temperature mean and variance increased community performance (i.e., growth rates), but did not affect maximum biomass. The results only partially support expectations from the variability framework. Additionally, no interactive effects of the N:P supply ratio and temperature were found, contrary to our hypothesis. Finally, we investigated how thermal variance and nutrient effects on phytoplankton communities differ between climatic regions. We showed that high nutrient concentrations and balanced N:P ratios allowed for an increase in performance in communities that experienced an increase in temperature mean, variance or both. However, when nutrient conditions are unbalanced or concentrations are low, responses to temperature treatments were highly dependent on the climatic region, suggesting that changes from replete and balanced resource supply lead to deviations from expectations in response to temperature regimes. Overall, this project contributes to the understanding of how variability in environmental conditions interacts with changes in mean mediating community responses to ongoing global change, including how the thermal performance and variability framework can be scaled up to closer to natural (ecologically relevant) scenarios.
Link to the final report
https://github.com/GerhardMiriam/Report_DFG_MGerhard
Publications
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Interview: "How Are We Pressuring Water Systems?" Saberes a la mesa, Vol. 3, issues 15 and 17.
Miriam Gerhard
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Panelist in Seminar: "Water, the Lifeblood of a World in Motion." Talk: "Impact of Multiple Factors on Water Bodies: From the Field to the Laboratory." Organized by: Center for Agroecology – Emmanuel Center, Colonia, Uruguay
Miriam Gerhard
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The experimental implications of the rate of temperature change and timing of nutrient availability on growth and stoichiometry of a natural marine phytoplankton community. Limnology and Oceanography, 69(8), 1769-1781.
Happe, Anika; Ahme, Antonia; Cabrerizo, Marco J.; Gerhard, Miriam; John, Uwe & Striebel, Maren
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Nutrient‐dependent thermal response in growth and stoichiometry of Antarctic phytoplankton. Limnology and Oceanography, 70(6), 1709-1724.
Smykala, Mike; Gerhard, Miriam & Plum, Christoph
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Panelist in Webinar, "21st Century Water and the Challenges Facing Uruguay." Talk: "Climate Change: Effects on Aquatic Ecosystems and Challenges for the Country."
Miriam Gerhard
