Phytoplankton growth and stoichiometric responses to warming, nutrient addition and grazing depend on lake productivity and cell size

Abstract

Global change involves shifts in multiple environmental factors that act in concert to shape ecological systems in ways that depend on local biotic and abiotic conditions. Little is known about the effects of combined global change stressors on phytoplankton communities, and particularly how these are mediated by distinct community properties such as productivity, grazing pressure and size distribution. Here, we tested for the effects of warming and eutrophication on phytoplankton net growth rate and C:N:P stoichiometry in two phytoplankton cell size fractions (<30 µm and >30 µm) in the presence and absence of grazing in microcosm experiments. Because effects may also depend on lake productivity, we used phytoplankton communities from three Dutch lakes spanning a trophic gradient. We measured the response of each community to multifactorial combinations of temperature, nutrient, and grazing treatments and found that nutrients elevated net growth rates and reduced carbon:nutrient ratios of all three phytoplankton communities. Warming effects on growth and stoichiometry depended on nutrient supply and lake productivity, with enhanced growth in the most productive community dominated by cyanobacteria, and strongest stoichiometric responses in the most oligotrophic community at ambient nutrient levels. Grazing effects were also most evident in the most oligotrophic community, with reduced net growth rates and phytoplankton C:P stoichiometry that suggests consumer‐driven nutrient recycling. Our experiments indicate that stoichiometric responses to warming and interactions with nutrient addition and grazing are not universal but depend on lake productivity and cell size distribution.

The importance of allochthonous organic matter quality when investigating pulse disturbance events in freshwater lakes: a mesocosm experiment

“…Despite the large number of studies quantifying seston nutrient content and ratios in lakes (Prater et al, 2017;Bergstro ¨m et al, 2018), direct analyses of this fraction in mesocosm studies are not that common (Schulhof et al, 2019;Minguez et al, 2020). In our study the HF treatment added seston N, also found in a recently published study (Minguez et al, 2020), whereas the alder tree leaf leachate source increased concentrations of P, as reported elsewhere (Mutschlecner et al, 2018;Navarro et al, 2019).…”

Larval fish body growth responses to simultaneous browning and warming

“…Instead, in the brown treatment, we observed a positive effect of warming on chlorophyll. Previous studies suggest that warming effects on phytoplankton vary (but are often negative) with nutrient supply, associated shifts in cell size, grazing pressure, and other factors (Bernhardt et al, 2018; Schulhof et al, 2019; Uszko et al, 2017). The contrasting lack of a positive effect on chlorophyll concentrations in the clear water treatments, where the highest zooplankton biomass was observed, suggests that zooplankton may remove potential warming effects on phytoplankton, unless limited by dark environments.…”

Distinct interaction effects of warming and anthropogenic input on diatoms and dinoflagellates in an urbanized estuarine ecosystem

“…In the context of global climate change, warming and increased anthropogenic input are major global change stressors to coastal marine ecosystems (Glibert, 2020; Griffith & Gobler, 2020; Schulhof et al, 2019; Wells et al, 2020). Considering the high abundance and ecological importance of diatoms and dinoflagellates in coastal waters, understanding the interactive effect of both warming and anthropogenic input to these phytoplankton is essential for evaluating the fate of coastal marine ecosystems in the future scenarios.…”