Effect of a glyphosate formulation on freshwater plankton: A community combined metric approach

Aim: The aim of this study was to experimentally assess the effects of glyphosate formulation on plankton composition by using different community parameters through a mesocosm experiment. Methodology: A 600 l mesocosm experiment was performed for 7 days, including a control (without glyphosate) and two concentrations of glyphosate. Results: Glyphosate caused a significant decrease in cladoceran density and a significant increase in rotifer, Chlorophyceae, and Euglenophyceae densities. In addition, zooplankton size diversity as well as microalgal evenness diminished. Interpretation: The decrease in cladoceran density may have benefited rotifers since they are less competitive for food resources. Moreover, the decrease in cladoceran foraging pressure over Chlorophyceae and Euglenophyceae may have benefited them. The different tolerances and competitiveness within the plankton components make the structure of this community a good indicator of environmental disturbance.

Plant Traits of Phalaris Arundinacea and Phragmites Australis – Examining Effects of Water Level, Salinity, and Soil Types in a Mesocosm Experiment

Knowledge about the distribution of species along rivers and estuaries is the basis for decisions in nature conservation, but also for nature-based coastal and shore protection. Along rivers and estuaries, abiotic conditions affect plant traits, especially close to the marsh edge, and thus determine the distribution of plant species. Phragmites australis and Phalaris arundinacea occur along the German Elbe in the inland river and in the estuary, but the distribution of both species is locally and regionally inhomogeneous. We therefore simulated abiotic conditions of respective Elbe sections in a mesocosm experiment and investigated the influence of soil type, salinity, water level, and plant provenance on plant traits of P. australis and P. arundinacea. We compared growth-related and mechanical plant traits of both species. Productivity of P. arundinacea was less affected by sandy soil than that of P. australis. P. australis was insensitive to salinity and water level fluctuations, while traits of P. arundinacea responded to these factors. Furthermore, mechanical properties within a species were mainly dependent on plant growth. P. arundinacea was more flexible than P. australis, which can be attributed to morphological differences and differences in plant tissue. Plant provenance did not affect the response of plant traits to abiotic conditions. Our study provides clues for understanding the distribution patterns of P. australis and P. arundinacea.

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

Extreme precipitation is occurring with greater frequency and intensity as a result of climate change. Such events boost the transport of allochthonous organic matter (allo-OM) to freshwater ecosystems, yet little is known about the impacts on dissolved organic matter (DOM) quality and seston elemental stoichiometry, especially for lakes in warm climates. A mesocosm experiment located in a Turkish freshwater lake was designed to simulate a pulse event leading to increased inputs of allo-OM by examining the individual effects of increasing water colour (HuminFeed®, HF), the direct effects of the extra energetic inputs (alder tree leaf leachate, L), and the interactions of the single treatment effects (combination of both sources, HFL), along with a comparison with unmanipulated controls. Changes in the DOM quality and nutrient stoichiometry of the allo-OM treatment additions was examined over the course of the experiments. Results indicated that there was an increase of high recalcitrant DOM components in the HF treatment, in contrast to an increase in less aromatic microbially derived molecules for the L treatment. Unexpectedly, seston C:P ratios remained below a severe P-limiting threshold for plankton growth and showed the same temporal pattern in all mesocosms. In contrast, seston N:P ratios differed significantly between treatments, with the L treatment reducing P-limiting conditions, whilst the HF treatment increased them. The effects of the combined HFL treatment indicated an additive type of interaction and chlorophyll-a was highest in the HFL treatment. Our results demonstrate that accounting for the optical and stoichiometric properties of experimental allo-OM treatments is crucial to improve the capacity to explain extrapolated conclusions regarding the effects of climate driven flooding on freshwater ecosystems in response to global climate change. Graphical abstract

A microbial mutualist within host individuals increases parasite transmission between host individuals: Evidence from a field mesocosm experiment

The interactions among host-associated microbes and parasites can have clear consequences for disease susceptibility and progression within host individuals. Yet, empirical evidence for how these interactions impact parasite transmission between host individuals remains scarce. We address this scarcity by using a field mesocosm experiment to investigate the interaction between a systemic fungal endophyte, Epichloe coenophiala, and a fungal parasite, Rhizoctonia solani, in leaves of a grass host, tall fescue. Specifically, we investigated how this interaction impacted parasite transmission under field conditions in replicated experimental host populations. Epichloe-inoculated populations tended to have greater disease prevalence over time, though this difference had weak statistical support. More clearly, Epichloe-inoculated populations experienced higher peak parasite prevalences than Epichloe-free populations. Epichloe conferred a benefit in growth; Epichloe-inoculated populations had greater aboveground biomass than Epichloe-free populations. Using biomass as a proxy, host density was correlated with peak parasite prevalence, but Epichloe still increased peak parasite prevalence after controlling for the effect of biomass. Together, these results suggest that within-host microbial interactions can impact disease at the population level. Further, while Epichloe is clearly a mutualist of tall fescue, it may not be a defensive mutualist in relation to R. solani.

A paradox of parasite resistance: Disease-driven trophic cascades increase the cost of resistance, selecting for lower resistance with parasites than without them

Most evolutionary theory predicts that, during epidemics, hosts will evolve higher resistance to parasites that kill them. Here, we provide an alternative to that typical expectation, with an explanation centered on resource feedbacks. When resistance is costly, hosts evolve decreasing resistance without parasites, as expected. But with parasites, hosts can evolve lower resistance than they would in the absence of parasites. This outcome arises in an eco-evolutionary model when four conditions are met: first, resistance has a fecundity cost (here, via decreased foraging/exposure rate); second, resources increase during epidemics via trophic cascades; third, increased resources magnify the benefit of maintaining a fast foraging rate, thereby magnifying the cost of evolving a slower foraging/exposure rate (i.e., resistance); fourth, that amplification of the cost outweighs the benefit of resistance. When these conditions are met, hosts evolve lower resistance than without parasites. This phenomenon was previously observed in a mesocosm experiment with fungal parasites, zooplankton hosts, and algal resources. Re-analyzing this experiment produced evidence for our model's mechanism. Thus, both model and experiment indicate that, via resource feedbacks, parasites can counterintuitively select against resistance.