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Nutrient availability and temperature are important drivers of phytoplankton growth and stoichiometry. However, the interactive effects of nutrients and temperature on phytoplankton have been analyzed mostly by addressing changes in average temperature, whereas recent evidence suggests an important role of temperature fluctuations. In a laboratory experiment, we grew a natural phytoplankton community under fluctuating and constant temperature regimes across 25 combinations of nitrogen (N) and phosphorus (P) supply. Temperature fluctuations decreased phytoplankton growth rate (rmax), as predicted by nonlinear averaging along the temperature–growth relationship. rmax increased with increasing P supply, and a significant temperature × P × N interaction reflected that the shape of the thermal reaction norm depended on nutrients. By contrast, phytoplankton carrying capacity increased with N supply and in fluctuating rather than constant temperature. Higher phytoplankton N:P ratios under constant temperature showed that temperature regimes affected cellular nutrient incorporation. Minor differences in species diversity and composition existed. Our results suggest that temperature variability interacts with nutrient supply to affect phytoplankton physiology and stoichiometry at the community level.

The effects of species diversity on ecosystem functioning have been broadly studied, mostly considering random artificial assemblages. However, natural communities are shaped by ecological interactions and environmental conditions often leading to nonrandom species extinctions. Here, we manipulated a natural phytoplankton community by generating a taxonomic diversity gradient based on rare species exclusions and conducted a mesocosm experiment to investigate the diversity effects on ecosystem functioning (resource use efficiency and biomass) under two nutrient levels. We quantified two functional traits (size and photosynthetic pigments) to evaluate the relation of functional diversity and ecosystem functioning. In a second experimental phase we simulated temperature fluctuations to assess the role of diversity on temporal stability of ecosystem functioning. We did not find a significant effect of diversity on ecosystem functioning and the temporal stability of ecosystem functioning, regardless of nutrient level. These results indicated that loss of biomass caused by rare species extinctions was compensated by the species retained in the diversity gradient. Phytoplankton size diversity was positively related to diversity, but this was not transferred into a positive diversity effect on ecosystem functioning. Additionally, the loss of species did not result in a loss of pigment diversity. The lack of a biodiversity-ecosystem functioning (BEF) relationship in our study may be due to the weak coupling of functional and species diversity and a low manifestation of functional diversity under the evaluated conditions. We emphasize that more realistic biodiversity loss scenarios in experiments can yield different results from those in classical BEF research paradigms.

The study of the structure and dynamics of cladoceran egg banks in South America began only 15 years ago and the amount of knowledge, in addition to being scarce, is widely spread over partially national journals, theses, and books, and thus partially unavailable. We conducted a review of the literature published for this region, focusing mainly on the methodological approaches that have been applied and describe the main findings already published. The different methodological approaches make data comparability difficult. However, a total of 77 egg morphotypes were identified in the published studies. Among the variety of methods used, we suggest to adopt as the standard procedure: 1) pre isolation of eggs from the sediments by the “Sugar Flotation Method;” 2) identification, enumeration, and sorting of egg morphotypes present in the sample; 3) individual hatching of each egg morphotype; 4) adult individual identification to the species level according to available keys; and 5) linking identified eggs to identified species’ adults. The absence of identification keys constitutes a challenge. Therefore, collaborative research with the aim of generating pictorial taxonomical support for Neotropical resting eggs are encouraged. We believe the adoption of the suggested protocol might facilitate this issue. An extremely low hatching success was reported for most studies and the factors triggering the break of dormancy in the resting eggs coming from permanent systems remain unknown. In conclusion, resting egg studies are a novel and promising field in South America, but with many challenges that need to be addressed.

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