Warming and oligotrophication cause shifts in freshwater phytoplankton communities

Abstract

While there is a lot of data on interactive effects of eutrophication and warming, to date, we lack data to generate reliable predictions concerning possible effects of nutrient decrease and temperature increase on community composition and functional responses. In recent years, a wide-ranging trend of nutrient decrease (re-oligotrophication) was reported for freshwater systems. Small lakes and ponds, in particular, show rapid responses to anthropogenic pressures and became model systems to investigate single as well as synergistic effects of warming and fertilization in situ and in experiments. Therefore, we set up an experiment to investigate the single as well as the interactive effects of nutrient reduction and gradual temperature increase on a natural freshwater phytoplankton community, using an experimental indoor mesocosm setup. Biomass production initially increased with warming but decreased with nutrient depletion. If nutrient supply was constant, biomass increased further, especially under warming conditions. Under low nutrient supply, we found a sharp transition from initially positive effects of warming to negative effects when resources became scarce. Warming reduced phytoplankton richness and evenness, whereas nutrient reduction at ambient temperature had positive effects on diversity. Our results indicate that temperature effects on freshwater systems will be altered by nutrient availability. These interactive effects of energy increase and resource decrease have major impacts on biodiversity and ecosystem function and thus need to be considered in environmental management plans.

Phytoplankton community responses to temperature fluctuations under different nutrient concentrations and stoichiometry

“…, Verbeek et al. ). Fundamentally, this means that at a given temperature, nutrients can change the height and the curvature of the population growth TRN (Thomas et al.…”

“…, Verbeek et al. ) or the effect of temperature variability independently (Vasseur et al. , Bernhardt et al.…”

“…In lentic ecosystems, phytoplankton biomass and growth can respond very rapidly to changes in nutrient and temperature conditions (Moss et al 2011, Cross et al 2015. Previous studies have either analyzed the temperature-nutrient interactions with regard to constant temperatures (Thomas et al 2017, Verbeek et al 2018 or the effect of temperature variability independently (Vasseur et al 2014, Bernhardt et al 2018b. We provide an experimental test using a natural phytoplankton community subjected to 25 nutrient regimes, each under constant and fluctuating temperature showing that temperature fluctuations have nonneutral consequences for resource uptake, growth and standing stocks.…”

“…Currently, our knowledge on thermal variability effects on phytoplankton is solely based on a single species studies at high nutrient supply (Bernhardt et al 2018b). Nutrient supply has empirically been shown to interact strongly with temperature , Marañ on et al 2018, Verbeek et al 2018. Fundamentally, this means that at a given temperature, nutrients can change the height and the curvature of the population growth TRN (Thomas et al 2017).…”

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

“…reports showing stronger effects of temperature on stoichiometry at low rather than high nutrient loads(De Senerpont-Domis et al, 2014;Verbeek et al, 2018). It is conceivable that when nutrients are in ample supply, enhanced metabolic rates from warming can be invested in growth, leading to enhanced biomass buildup.…”