Beyond the mean: phytoplankton responses to fluctuating resource and energy supply
Final Report Abstract
While some fundamental studies explored how pulsed resource supply alters community composition and performance, these considerations have rarely been placed in a warming-resource context, and none explicitly addressed fluctuations in more than one dimension. This project aimed to evaluate the interactive effect of resources (nutrients and light) and (fluctuating) temperature on freshwater phytoplankton. First, we investigated how temperature, light and nutrients directly and indirectly affect the growth of two phytoplankton species. We identified temperature and light as the dominant factors for an increase in growth rate, temperature as the main factor for a reduction in cell size, and nutrient availability for changes in cell stoichiometry. Next, we investigated the combined impact of temperature, light, and nutrients on the growth of four species and found that temperature modulated the interactive effect of light and nutrients. Balanced resource ratios generally led to higher growth and as temperature increased, both the positive response to balanced ratios and the negative response to imbalanced ratios were intensified. These results underscore the necessity of considering multiple factors to understand phytoplankton responses and demonstrate that temperature has a significant impact on how resources are required and utilized. Further, we tested how resource availability (light and nutrients) shapes the growth response to constant and variable temperatures. We found a resource-dependent effect of temperature variability, with light being the dominant factor. Under light-reduced conditions, growth was higher under constant than under variable temperatures. Exposing a natural plankton community to pulsed nutrient addition combined with two treatments of fluctuating light conditions, we assumed that phytoplankton biomass decreases under fluctuating conditions as the fluctuations happen faster than the adaptation. The results showed that natural conditions even exhibited more variability as we were able to apply within our experimental setup and no treatment-dependent differences could be observed with daily biomass measurements. However, high resolution oxygen data allowed us to resolve treatment effects on phytoplankton responses. In sum, the results from this project provide important insights into how variability in different regions, characterized by different resource availabilities and temperatures, can affect phytoplankton and, consequently, the aquatic food web.
Publications
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2022. Temperature drives co-limitation of light and nutrients in phytoplankton. Oral presentation, DGL conference, Konstanz, Germany
Heinrichs et al.
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2022. Temperature drives co-limitation of light and nutrients in phytoplankton. Oral presentation, SIL conference, Berlin, Germany
Heinrichs et al.
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2023. Effects of fluctuating temperatures are modulated by the availability of light and nutrients. Oral presentation, ASLO conference (Aquatic science meeting), Palma de Mallorca, Spain
Heinrichs et al.
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Direct and indirect cumulative effects of temperature, nutrients, and light on phytoplankton growth. Ecology and Evolution, 14(8).
Heinrichs, Anna Lena; Hardorp, Onja Johannes; Hillebrand, Helmut; Schott, Toni & Striebel, Maren
