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Horizontal gene transfer (HGT) is a major process by which genes are transferred between microbes in the rhizosphere. However, examining HGT remains challenging due to the complexity of mimicking conditions within the rhizosphere. Fabricated ecosystems (EcoFABs) have been used to investigate several complex processes in plant-associated environments. Here we show that EcoFABs are efficient tools to examine and measure HGT frequency in the rhizosphere. We provide the first demonstration of gene transfer via a triparental conjugation system in the Brachypodium distachyon rhizosphere in an EcoFAB using Pseudomonas putida KT2440 as both donor and recipient bacterial strain with the donor containing a mobilizable and non-self-transmissible plasmid. We observed that the frequency of plasmid transfer in the rhizosphere is potentially dependent on the plant developmental stage and the composition and amount of root exudates. The frequency of plasmid transfer also increased with higher numbers of donor cells. We demonstrate the transfer of plasmid from P. putida to another B. distachyon root colonizer, Burkholderia sp. OAS925, showing HGT within a rhizosphere microbial community. Environmental stresses also influenced the rate and efficiency of HGT in the rhizosphere between different species and genera. This study provides a robust workflow to evaluate transfer of engineered plasmids in the rhizosphere when such plasmids are potentially introduced in a field or other plant-associated environments.IMPORTANCEWe report the use of EcoFABs to investigate the HGT process in a rhizosphere environment. It highlights the potential of EcoFABs in recapitulating the dynamic rhizosphere conditions as well as their versatility in studying plant-microbe interactions. This study also emphasizes the importance of studying the parameters impacting the HGT frequency. Several factors such as plant developmental stages, nutrient conditions, number of donor cells, and environmental stresses influence gene transfer within the rhizosphere microbial community. This study paves the way for future investigations into understanding the fate and movement of engineered plasmids in a field environment.

The processing of organic matter is a central ecosystem function in freshwater ecosystems that allows the integration of terrestrial plant material into aquatic heterotrophic food webs. From an energetic perspective, many temperate aquatic systems fundamentally depend on such allochthonous inputs. Current research established that this central ecosystem function may be linked to population density of few yet dominant invertebrate detritivores, showing a negative density‐dependent relationship. Here, we extended the current knowledge and experimentally assessed the processing of leaf litter by freshwater amphipods, using broad density gradients, interspecific competition, and laboratory and field experiments. We used two species of dominant amphipods, namely the native Gammarus fossarum and the non‐native Gammarus roeselii, varying their density by two orders of magnitude, both in single‐species and two‐species treatments. Results from 252 mesocosms in the lab and 97 mesocosms in a natural stream show that per capita leaf litter processing rates are strongly negatively dependant on population density in monocultures. Interspecific competition in two‐species treatments corroborated the negative density‐dependent ecosystem function and highlighted the functional redundancy of the two detritivore species. We identified a flattening in the processing rates at previously unreported but well‐defined breakpoints. These breakpoints may reflect minimal metabolic requirements at which survival takes precedence over any other process, such as interference competition. The breakpoints were consistent across both species, indicating that they must process leaf litter equalling one fifth to one fourth of their dry body weight per day as a minimal nutritional threshold. Our results suggest the need for integrating nonlinear density‐dependencies and breakpoint population densities in key ecosystem functions in aquatic ecosystem modelling alongside classical biodiversity–ecosystem functioning relationships. Depending on the population density the corresponding ecosystem functioning could differ significantly. This corroborates the need to better understand biodiversity–abundance relationships when protecting aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Industrial microbes and bio-derived products have emerged as an integral component of the bioeconomy, with an array of agricultural, bioenergy, and biomedical applications. However, the rapid development of microbial biotechnology raises concerns related to environmental escape of laboratory microbes, detection and tracking thereof, and resultant impact upon native ecosystems. Indeed, though wild-type and genetically modified microbes are actively deployed in industrial bioprocesses, an understanding of microbial interactivity and impact upon the environment is severely lacking. In particular, the persistence and sustained ecosystem impact of industrial microbes following laboratory release or unintentional laboratory escape remains largely unexplored. Herein, we investigate the applicability of soil-sorghum mesocosms for the ecological risk assessment of the industrial microbe, Saccharomyces cerevisiae. We developed and applied a suite of diagnostic and bioinformatic analyses, including digital droplet PCR, microscopy, and phylogenomic analyses to assess the impacts of a terrestrial ecosystem perturbation event over a 30-day time course. The platform enables reproducible, high-sensitivity tracking of S. cerevisiae in a complex soil microbiome and analysis of the impact upon abiotic soil characteristics and soil microbiome population dynamics and diversity. The resultant data indicate that even though S. cerevisiae is relatively short-lived in the soil, a single perturbation event can have sustained impact upon mesocosm soil composition and underlying microbial populations in our system, underscoring the necessity for more comprehensive risk assessment and development of mitigation and biocontainment strategies in industrial bioprocesses. [ABSTRACT FROM AUTHOR]

Ecosystems worldwide are experiencing a range of natural and anthropogenic disturbances, many of which are intensifying as global change accelerates. Ecological responses to those disturbances are determined by both the vulnerabilities of species and their interspecific interactions. Understanding how individual species contribute to the (in‐)stability of an aggregated community property, or function, is fundamental to ecological management and conservation. Here, we present a framework to identify species contributions to stability based on their absolute and relative responses to disturbances. Using simulations, we show that these two dimensions enable identification of (de‐)stabilizing species and reveal that competitive dominance determines the magnitude of both absolute and relative contributions to stability. Applying our framework to empirical data from a multi‐site mesocosm experiment showed that species contributions varied among treatments, sites, and seasons. Despite this dependency on both biotic and abiotic contexts, species contributions were generally constrained by their relative dominance in undisturbed conditions. Rare species contributed positively to stability, while dominant species contributed negatively, indicating compensatory dynamics. Our framework offers an important step toward a more mechanistic understanding of ecological stability based on species performance. [ABSTRACT FROM AUTHOR]

Domestic and industrial effluents contain substantial amounts of micropollutants, such as pharmaceuticals, which may influence the balance of the phytoplankton community. A mesocosm approach was used to determine the effects of different fluoxetine concentrations (20 ng L−1, 20 µg L−1, and 20 mg L−1) on phytoplankton community structure, biochemical composition, antioxidant response, and primary productivity. The total cell density of the phytoplankton community was in the order of control > 20 µg > 20 ng > 20 mg by the 21st day of the experiment. On day 21, the phytoplankton community had chlorophyll a content in the order of 20 mg > 20 µg > 20 ng > control, but these changes were not significant (p > 0.05). Beta diversity results revealed that fluoxetine significantly affected the community structure and dynamics of exposed phytoplankton. Reactive oxygen species, malondialdehyde and peroxidase levels were significantly altered by changes in fluoxetine concentrations. Protein content increased at 20 µg L−1 and decreased at 20 ng L−1 and 20 mg L−1 by day 21 of the experiment. These results suggest that, even in the ng L−1 range, fluoxetine could contribute to the reshaping of phytoplankton community structure and dynamics in aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Pollination is a key tenet of ecosystem sustainability and food security, but it is threatened by climate change. While many studies investigated the response of plant‐pollination traits to temperature, few attempted multifactorial and integrative approaches with multiple floral traits. We determined which plant‐pollination traits were disrupted by environmental changes and the consequence for plant fitness. We focused on the thermogenic plant, Arum italicum, which relies on floral scent and heat production to attract its pollinators with a deceptive strategy. In a field mesocosm, we measured the response of floral phenology, thermogenesis traits, scent and plant fitness to experimental changes in shade level, water supply and soil temperature. In the laboratory, we exposed plants to extreme heat to determine the thermoregulation ability at high temperatures. Plant fitness decreased dramatically in response to soil warming and the level of shade. While both factors caused a lower number of inflorescences, soil warming was mostly responsible for the crash in number of fruits. The plant traits related to thermogenesis and scent were relatively resilient to the environmental changes in the mesocosm and were unlikely to produce the observed decrease in plant fitness. First, environmental changes only weakly modified the scent composition. Second, the appendix regulated its maximal temperature almost perfectly, while stamen regulated imperfectly. In the laboratory experiment, the appendix maintained a thermal gradient supposedly to improve scent emission while stamen became cooler than ambient air, possibly preventing the pollinators from overheating within the floral chamber. By contrast, the phenology of flowering was drastically modified. Flowers appeared earlier in the season in response to soil warming (by 39 days) or absence of shade (by 19 days). At the daily scale, flowering hour did not change across the season resulting in plants flowering before sunset late in the season and before the pollinator activity window (mostly nocturnal). The strong shift observed in the flowering period may induce a temporal mismatch with this pollinator both early and late in the season when the insects may not be active so early in the spring and during daytime, respectively, thereby altering plant fitness. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Assessing social effects on individual behaviour is challenging because knowledge of an individual's social environment is often difficult to gain, especially for animals that form dynamic social groups. We here report on an experiment where the social environment could be manipulated. To this end, we capitalized on the availability of populations of migrant and resident sticklebacks, Gasterosteus aculeatus , that exhibit strong differences in movement tendencies. This allowed us to create mixed shoals with different proportions of migrants and residents, to investigate the occurrence of social effects between migrant and resident fish. In a mesocosm consisting of linearly connected ponds, we found that the overall movement patterns, as quantified by the number of pond transitions, remained consistently higher in migrants than in residents, regardless of the social group composition. The fish's intrinsic movement tendency was the main predictor of the observed variation between populations. However, at the start of the experiment, when social effects were expected to be strongest, residents were more likely to leave the starting pond in the presence of migrants than in their absence. As this increase in movement tendency was not related to the frequency of migrants in the mixed groups it cannot solely be ascribed to social conformity. Additionally, we found an effect of being part of the majority on movement: the first fish to leave the starting pond was almost always a member of the majority group (be it migrants or residents). In conclusion, we found little evidence for social modulation of movement based on differences in the populations' movement tendencies, but rather an effect of being in a majority group. • We experimentally manipulated the social environment under seminatural conditions. • Movements between ponds remained consistently higher in migratory fish. • Residents were more likely to leave the starting pond in the presence of migrants. • Habituation to the experimental set-up likely played a role. • The first fish to leave the starting pond was almost always from the majority group. [ABSTRACT FROM AUTHOR]

Wetlands are important ecosystems for mitigating climate change impacts on the environment and society. Most studies focus on how single environmental factors affect those ecosystems, although several environmental factors may change simultaneously. This study focused on nutrient – water level interaction effects on two different but associated wet grassland species Carex acuta and Glyceria maxima. Biomass allocation and root exudates were measured in a full-factorial mesocosm experiment. Species identity and water level mostly determined total alive biomass and the biomass allocation pattern. Root weight ratio generally increased in C. acuta whereas increased rhizome biomass was associated with G. maxima. Furthermore, increased water levels increased relative aboveground biomass allocation with C. acuta having more leaf and G. maxima having more stem biomass. Surprisingly, fertilisation had little impact on total biomass, but decreased relative biomass allocation to the roots and also strongly suppressed root exudation. There is an apparent nutrient dependent shift in the realised hydrological niche of both plants towards drier conditions. C. acuta behaves similar under all water levels without fertilisation, but thrives best under dry conditions when fertilised. Without fertilisation, G. maxima thrives best under flooded conditions (water level ~ 15 cm above soil surface), but does equally well in saturated water conditions (water level ~ soil surface) when fertilised. [ABSTRACT FROM AUTHOR]

As climate change intensifies heatwaves, quantifying associated mortality within ectothermic populations is crucial for effective conservation. Thermal tolerance landscape (TTL) models are useful predictive tools that assume exponentially decreasing survival durations in individuals with increasing temperatures. This assumption has been validated through regression analyses on data from constant temperature experiments, primarily focusing on adult‐stage individuals. However, this approach does not allow for direct model validation with data from dynamic, real‐world heatwave events and overlooks early recruitment stage vulnerabilities.This study aimed to address these gaps using the blue mussel Mytilus, a foundation species forming extensive reefs along temperate coasts, as a model organism. We monitored survival rates of mussels (juveniles and adults) under constant heatwave (CHW) conditions in a laboratory experiment and under dynamic heatwave (DHW) scenarios simulated in an outdoor mesocosm experiment. Post‐heatwaves, we also assessed recruitment rates within the mesocosms. TTL models were parametrised by employing Approximate Bayesian Computation with Sequential Monte Carlo (ABC‐SMC) on each dataset separately.The parameter distributions were similar across both experiments, and the ABC‐SMC model predictions closely matched the observed survival declines, validating these models. In comparison, we found a lower predictive performance when using a Bayesian regression approach. Additionally, our best‐fit model predicted that warming across the non‐fatal DHW regimes would increase sublethal effects on mussels. The observed impact on the recruitment stage was more pronounced, with the recruitment rate following an exponential decay as sublethal effects increased. Our model projected minor (<4%) sublethal effects in adult mussels during the century's five warmest summer temperature regimes, corresponding to 0%–32% declines in recruitment rates.Our research extends the TTL model validation, demonstrates the resilience of subtidal Baltic Mytilus to future extreme heatwaves and offers an approach to predict heatwave‐induced population mortalities, applicable to other species and sensitive systems. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

We examined the interactions between stream water and subsurface sediment to quantify how these interactions influenced organic C respiration and dissolved inorganic C (DIC) production in the hyporheic zone of a high-gradient headwater mountain stream draining a forested catchment at the H. J. Andrews Experimental Forest, Oregon, USA. We compared measurements from a well network with those from six 2-m-long hyporheic mesocosms. The patterns in hyporheic metabolism were similar in wells and mesocosms: O2 declined and DIC increased with travel time. However, the dissolved organic C (DOC) showed little net change in concentration. The mesocosms showed that net losses of DOC could account for 7% of O2 consumed during summer and autumn and 24% of O2 consumed in the winter and spring. Previous research at our study site suggested that large volumes of hyporheic exchange are likely to result in continual processing of streamwater DOC through the hyporheic zone, which would limit the accumulation of bioavailable DOC. Consequently, hyporheic respiration in this forested headwater stream appears to rely primarily on organic C ultimately derived from sediment-bound or buried particulate organic matter (POC). We modeled the consumption of O2 (k O2) and the production of DIC (k DIC) as zero-order kinetic reactions. In the mesocosms, k O2 and k DIC were correlated to temperature and were 2× higher in the summer and autumn than in the winter and spring. In the well network, however, neither k O2 nor k DIC showed seasonal differences. The k DIC was also correlated to initial DOC concentrations in both the mesocosms and the wells. Further, the k DIC was correlated to the time since the mesocosms were packed, which suggests that sediment disturbance or incorporation of relatively fresh organic matter from packing the mesocosms increased the bioavailability of the POC. Further, changes in concentrations of O2, DOC, and DIC were approximately linear when plotted against travel time for both the mesocosms and the well field. These data suggest that the processes that release bioavailable DOC from POC are relatively constant along hyporheic flow paths and govern the rate of hyporheic metabolism in the hyporheic zone of this forested headwater stream. [ABSTRACT FROM AUTHOR]

When cyanobacterial phytoplankton form harmful cyanobacterial blooms (HCBs), the toxins they produce threaten freshwater ecosystems. Hydrogen peroxide is often used to control HCBs, but it is broadly toxic and dangerous to handle. Previously, we demonstrated that glucose addition to lake water could suppress the abundance of cyanobacteria. In this study, glucose was compared to hydrogen peroxide for the treatment of cyanobacterial phytoplankton communities. The six-week study was conducted in the large mesocosms facility at Grand Valley State University's Annis Water Resources Institute in Michigan. To 1000 L of Muskegon Lake water, glucose was added at either 150 mg or 30 mg glucose/L. Hydrogen peroxide was added at 3 mg/L to two 1000 L mesocosms. And two mesocosms were left untreated as controls. Triplicate 100 mL samples were collected weekly from each mesocosm, which were then filtered and frozen at −80 °C for 16S rRNA amplicon sequencing. The 16S rRNA amplicon sequencing results revealed that hydrogen peroxide treatment quickly reduced the relative abundance of the cyanobacteria compared to the control mesocosms, but the cyanobacteria population returned over the course of the 6-week study. On the other hand, both glucose concentrations caused a rapid proliferation of multiple low abundance proteobacterial and bacteroidotal taxa resulting in notable increases in taxonomic richness over the duration of the study and reducing the relative abundance of cyanobacteria. Although hydrogen peroxide quickly suppressed the cyanobacteria, the population later returned to near starting levels. The glucose suppressed the cyanobacterial phytoplankton apparently by promoting competitive heterotrophic bacteria. [ABSTRACT FROM AUTHOR]

Mosquitoes are known to choose oviposition habitats actively based on their suitability for survival of their offspring. They thus avoid laying eggs in dangerous habitats with aquatic predators through detection of their cues. Visual, tactile, and chemical cues emitted by certain predators have been shown to reduce oviposition in some mosquitoes, which in turn may affect their adult population sizes. However, those tests tend to be limited to species from temperate regions. Moreover, mosquito oviposition response to predator cues have been shown to be predator specific, but this has not been investigated for many potential predators worldwide. In the African subtropics, temporary ponds can be important mosquito breeding habitats and the same habitats are also used by a group of specialized killifish that can survive dry periods using drought resistant eggs. Although they are reported as mosquito predators, it is unknown whether mosquitoes actively avoid laying eggs in ponds with annual killifish. We investigated this using the mosquito Culex quinquefasciatus and the free and caged killifish Nothobranchius neumanni in the outdoor mesocosm experiments in Tanzania. We found that Cx. quinquefasciatus had 71% lower oviposition in mesocosms with free swimming killifish and 68% lower oviposition in mesocosms with caged killifish. We conclude that predator-released chemical cues alone are enough to explain the observed responses. If the cues can be isolated and chemically identified can be developed into a biological mosquito control strategy and used to safeguard public health in areas where mosquito borne diseases are endemic. [ABSTRACT FROM AUTHOR]

The gradual accumulation of phosphorus from historical fertilization can contribute to the eutrophication of surface waters by increasing the potential for subsurface leaching losses. Grazing lands areas are a priority for concern, and phytoremediation efforts in grazing lands have prioritized grasses that may be used as forage for cattle. This study investigated the influence of three different forage species—Paspalum notatum, Hemarthria altissima, and Cynodon nlemfuensis—on the loss of phosphorus in leachate from surface soils. The experiment used a nested pot mesocosm design that allowed us to monitor leachate volume and concentration biweekly over the course of 3 months. Pots containing P. notatum plants leached significantly more phosphorus than pots containing C. nlemfuensis or empty pots with no plants growing in them, despite losing an equivalent amount of water. H. altissima lost equivalent amounts of phosphorus in leachate water, but each H. altissima plant removed approximately 33.6 mg of phosphorus, approximately 2.5× that removed by P. notatum (13.4 mg). C. nlemfuensis had lower average leachate phosphorus concentrations at each biweekly sampling than either plant species (C. nlemfuensis‐P. notatum, padj = 0.001; C. nlemfuensis‐H. altissima, padj = 0.02), averaging only 0.110 ppm in leachate relative to 0.175 ppm and 0.200 ppm in pots beneath H. altissima and P. notatum, respectively. This, combined with C. nlemfuensis' slightly higher‐than‐average aboveground P content and overall aboveground biomass expression suggest it is the best possible phytoremediation candidate. As even minor leachate P loads can be critically threatening to neighboring oligotrophic water bodies, if the conservation of downstream environments is the priority, the short‐term threat of increased leachate must be considered. Further research is needed to explore the underlying mechanisms and field‐scale implications of these findings. [ABSTRACT FROM AUTHOR]

Temperature is commonly acknowledged as one of the primary forces driving ectotherm vector populations, most notably by influencing metabolic rates and survival. Although numerous experiments have shown this for a wide variety of organisms, the vast majority has been conducted at constant temperatures and changes therein, while temperature is far from constant in nature, and includes seasonal and diurnal cycles. As fluctuating temperatures have been described to affect metabolic processes at (sub)cellular level, this calls for studies evaluating the relative importance of temperature fluctuations and the changes therein. To gain insight in the effects of temperature fluctuations on ectotherm development, survival, and sex ratio, we developed an inexpensive, easily reproducible, and open‐source, Arduino‐based temperature control system, which emulates natural sinusoidal fluctuations around the average temperature. We used this novel setup to compare the effects of constant (mean) temperatures, most commonly used in experiments, block schemes, and natural sinusoidal fluctuations as well as an extreme variant with twice its amplitude using the cosmopolitan mosquito species Culex pipiens s.l. as a study organism. Our system accurately replicated the preprogrammed temperature treatments under outdoor conditions, even more accurately than traditional methods. While no effects were detected on survival and sex ratio within the ranges of variation evaluated, development was sped up considerably by including temperature fluctuations, especially during pupation, where development under constant temperatures took almost a week (30%) longer than under natural fluctuations. Doubling the amplitude further decreased development time by 1.5 days. These results highlight the importance of including (natural) oscillations in experiments on ectotherm organisms – both aquatic and terrestrial – that use temperature as a variable. Ultimately, these results have major repercussions for downstream effects at larger scales that may be studied with applications such as ecological niche models, disease risk models, and assessing ecosystem services that rely on ectotherm organisms. [ABSTRACT FROM AUTHOR]

The phosphorus (P) concentration is increasing in parts of the Baltic Sea following the spring bloom. The fate of this excess P-pool is an open question, and here we investigate the role of microbial degradation processes in the excess P assimilation phase. During a 17-day-long mesocosm experiment in the southwest Finnish archipelago, we examined nitrogen, phosphorus, and carbon acquiring extracellular enzyme activities in three size fractions (<0.2, 0.2–3, and >3 µm), bacterial abundance, production, community composition, and its predicted metabolic functions. The mesocosms received carbon (C) and nitrogen (N) amendments individually and in combination (NC) to distinguish between heterotrophic and autotrophic processes. Alkaline phosphatase activity occurred mainly in the dissolved form and likely contributed to the excess phosphate conditions together with grazing. At the beginning of the experiment, peptidolytic and glycolytic enzymes were mostly produced by free-living bacteria. However, by the end of the experiment, the NC-treatment induced a shift in peptidolytic and glycolytic activities and degradation of phosphomonoesters toward the particle-associated fraction, likely as a consequence of higher substrate availability. This would potentially promote retention of nutrients in the surface as opposed to sedimentation, but direct sedimentation measurements are needed to verify this hypothesis. [ABSTRACT FROM AUTHOR]

Dispersal success is crucial for the survival of species in metacommunities. Zooplankton species engage in dispersal through time (i.e., egg bank) and space (i.e., vectors) by means of resting eggs. However, dispersal to patches does not equate to successful colonization, as there is a clear distinction between dispersal rates and successful colonization. We performed a field mesocosm experiment assessing dispersal and colonization success of zooplankton from resting eggs or transport via directional wind/airborne and biotic vectors in the vicinity of three ponds. By using active vs. sterile pond sediments and mesh-covered vs. open mesocosms, we disentangled the two mechanisms of dispersal, i.e., from the egg bank vs. space. We found that for both rotifers and cladocerans, sediment type, mesh cover and duration of the experiment influenced species richness and species composition. The relative contribution of resting stages to dispersal and colonization success was substantial for both rotifers and cladocerans. However, wind/airborne dispersal was relatively weak for cladocerans when compared to rotifers, whereas biotic vectors contributed to dispersal success especially for cladocerans. Our study demonstrates that dispersal and colonization success of zooplankton species strongly depends on the dispersal mode and that different dispersal vectors can generate distinct community composition. [ABSTRACT FROM AUTHOR]

This paper presents the results of a mesocosm experiment for the evaluation of remote sensing chlorophyll-a (chl-a) concentration estimations in an anthropogenic water reservoir. The chl-a presence in the water causes changes in the water surface reflectance spectrum, especially in the green and red part, but many factors could affect the remote measurements of chl-a content. The in situ mesocosm method of the experiment was used for investigating the spectral reflectance of the inland water surface in a wide range of chl-a concentrations. Eight specially designed measurement boxes were placed into the water. In half of the boxes, the devices to support the development of the submerged water plant were installed. During the experiment, simultaneously, spectral data from the water surface were gathered and physical–chemical analyses of water were carried out. The obtained results confirm the usefulness of the mesocosm experiment for the remote sensing chl-a concentration algorithms being developed. The concentration of dissolved organic carbon was identified as a key factor that interfered with remote chl-a estimations in the analyzed reservoir. [ABSTRACT FROM AUTHOR]

Aedes albopictus mosquitoes face numerous anthropic stressors in urban areas. These xenobiotics not only impact mosquito physiology but also shape the composition of their microbiota, which play important roles in host physiological traits. Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants known to alter mosquito metabolism, but no studies have yet investigated their impact on microbiota. Using a bespoke indoor mesocosm tailored for Ae. albopictus mosquitoes, we investigated the dynamics of bacterial communities in both mosquitoes and their larval breeding sites following chronic exposure to a cocktail of PAHs consisting of benzo[a]pyrene, benz[a]anthracene, chrysene and benzo[b]fluoranthene. Our findings showed that PAHs have a stage-specific effect on mosquito microbiota, with a higher impact in larvae than in adults, contributing to 12.5 % and 4.5 % of the PAHs-induced variations, respectively. The presence of PAHs in the treated mesocosm led to the enrichment of bacterial families and genera known for their ability to catabolize PAHs, such as Comamonadaceae and Raoultella (increasing from 19 % to 30 % and from 1.2 % to 5.6 %, respectively). Conversely, prevalent taxa found in mosquito microbiota like Wolbachia and Cedecea exhibited a reduction (decreasing from 4 % to 0.8 % and from 12.8 % to 6.4 %, respectively). This reduction could be attributed to the competitive advantage gained by PAH-degrading taxa, or it could reflect a direct sensitivity to PAH exposure. Overall, this indicates a shift in microbiota composition favoring bacteria that can thrive in a PAH-contaminated environment. PAHs persisted in the water of breeding sites only the first 45 days of the experiment. Benzo[a]pyrene and benzo[b]fluoranthene were more susceptible to bioaccumulation in larval tissues over time. Overall, this study enhances our understanding of the impact of pollution on mosquitoes and could facilitate future research on the importance of symbiosis in urban-dwelling insect disease vectors. Given the recent advancements in the generation of axenic (microbe-free) and gnotobiotic (mosquitoes with a defined or specific microbiota) mosquitoes, further studies are needed to explore how changes in microbiota composition could influence mosquito responses to pollution, particularly in relation to host fitness, immunity, and vector competence.

Abstract Background A recently published article, by Reiber et al., on the representativity of macroinvertebrate communities in outdoor micro- or mesocosm studies, used as a higher tier tool in the environmental risk assessment of plant protection products (PPPs) in the EU, concluded that ‘micro-/mesocosm studies do not represent natural macroinvertebrate communities’. Fundamentally, the article based its conclusion on the analysis of data from 26 streams used in a monitoring project in Germany (2018–2019), in comparison to taxa found in seven lentic micro- and mesocosm studies, conducted at four test sites (2013 – 2018), and submitted to the UBA, Germany. Results There are multiple reasons why this conclusion is incorrect, e.g. the number of taxa, for which the Minimum Detectable Differences (MDDs) were low enough to allow a detection of direct effects in the seven lentic mesocosm studies, cannot be compared to the number of taxa just present in at least five of 26 streams. We have further investigated the data from five of the seven studies which were analysed in detail by Reiber et al. and determined that the MDDs of 12 to 18 invertebrate taxa per study fulfilled the current recommendation to allow a detection of medium effects (MDD up to 70%). However, which taxa can be considered potentially sensitive depends on the specific test item. While lentic test systems may not be suitable to test effects on typical stream taxa, taxa occurring in lentic systems such as ponds and ditches are not by definition less sensitive, or vulnerable, to pesticides than taxa living in streams, and their relative sensitivity can be checked in laboratory tests, or artificial streams, if needed. Conclusions In our view, well conducted micro- and mesocosm studies do provide reliable and useful data for the environmental risk assessment of plant protection products covering long-term, as well as indirect, effects under semi-natural conditions.

Amphibians are declining worldwide, and research on their habitats and ecology is important for their conservation. The endangered dusky gopher frog (Rana sevosa) breeds exclusively in isolated, open canopy wetlands, usually with extensive herbaceous growth. Larvae of the dusky gopher frog have higher growth and survival under open canopy than under closed canopy conditions. The mechanisms whereby this occurs are poorly understood, however. In the summer of 2021 in Harrison County, Mississippi, USA, we conducted a complete factorial experiment in mesocosms to compare the relative influence of factors differing between open and closed canopy ponds on larvae. A heat and light treatment consisted of one third of tanks being exposed to full sunlight, one third of tanks being shaded with 70% shadecloth, and the final third being shaded with 70% shadecloth but heated to mimic the temperature of the full sun tanks. In addition, tanks received a closed canopy tree leaf litter mixture or an open canopy herbaceous vegetation mixture, and vertical vegetation‐like structure made of polypropylene rope or not. Cool shaded tanks and heated shaded tanks had identical survival to metamorphosis at 74.7% and produced frogs with an average mass of 2.21 g and 2.09 g, respectively, while tanks in full sunlight achieved significantly higher 93.4% survival to metamorphosis and an average mass of 2.64 g. The open canopy vegetation mixture yielded an average tank survival of 88.3% and mass of 2.94 g, compared to closed canopy vegetation tanks with a significantly lower survival of 73.5% and average mass of 1.61 g. Added structure had no effect on survival or mass. These results indicate that sunlight (not heat alone) and herbaceous plants are important in increasing dusky gopher frog survival and mass in open canopy conditions and suggest that management for these characteristics receive priority in captive‐rearing programs and habitat restoration. [ABSTRACT FROM AUTHOR]

All over the world, peatlands have been drained, often for agricultural purposes, resulting in CO2 emissions, soil subsidence and biodiversity loss. To combat these negative effects, drained peatlands are being rewetted, but knowledge of the effects of rewetting on peat biogeochemistry is still incomplete, especially since a variety of rewetting methods and rewetting degrees exists. We conducted a mesocosm experiment in which we exposed 100 intact agricultural fen peat cores (80 cm, 20 cm Ø) to five different water levels (0, 20, 40, 60 cm and variable—surface), two nutrient application levels to mimic continued agricultural use, and two water origins. Over an eight-month period, we harvested above-ground plant biomass five times and sampled pore water at two depths each month. Samples were analysed for nutrients. Our results show increased phosphate and ammonium availability upon fully rewetting (0 cm—surface) and less so under partially rewetted circumstances (20 cm—surface). Above-ground biomass was strongly affected by nutrient application, especially in the high water level treatments. Vegetation was primarily N-limited, and N in the vegetation decreased with increasing water levels, indicating stronger nitrogen limitation upon rewetting. We conclude that nature restoration under fully rewetted conditions will likely be challenging as a result of the large release of nutrients from the system which may also affect surrounding nature areas. Furthermore, we conclude that partial rewetting combined with low-intensity agricultural use can be a solution to slow down the adverse effects of drainage, although this will lead to decreased agricultural production. [ABSTRACT FROM AUTHOR]

Background: A recently published article, by Reiber et al., on the representativity of macroinvertebrate communities in outdoor micro- or mesocosm studies, used as a higher tier tool in the environmental risk assessment of plant protection products (PPPs) in the EU, concluded that 'micro-/mesocosm studies do not represent natural macroinvertebrate communities'. Fundamentally, the article based its conclusion on the analysis of data from 26 streams used in a monitoring project in Germany (2018–2019), in comparison to taxa found in seven lentic micro- and mesocosm studies, conducted at four test sites (2013 – 2018), and submitted to the UBA, Germany. Results: There are multiple reasons why this conclusion is incorrect, e.g. the number of taxa, for which the Minimum Detectable Differences (MDDs) were low enough to allow a detection of direct effects in the seven lentic mesocosm studies, cannot be compared to the number of taxa just present in at least five of 26 streams. We have further investigated the data from five of the seven studies which were analysed in detail by Reiber et al. and determined that the MDDs of 12 to 18 invertebrate taxa per study fulfilled the current recommendation to allow a detection of medium effects (MDD up to 70%). However, which taxa can be considered potentially sensitive depends on the specific test item. While lentic test systems may not be suitable to test effects on typical stream taxa, taxa occurring in lentic systems such as ponds and ditches are not by definition less sensitive, or vulnerable, to pesticides than taxa living in streams, and their relative sensitivity can be checked in laboratory tests, or artificial streams, if needed. Conclusions: In our view, well conducted micro- and mesocosm studies do provide reliable and useful data for the environmental risk assessment of plant protection products covering long-term, as well as indirect, effects under semi-natural conditions. [ABSTRACT FROM AUTHOR]

Abstract The gradual accumulation of phosphorus from historical fertilization can contribute to the eutrophication of surface waters by increasing the potential for subsurface leaching losses. Grazing lands areas are a priority for concern, and phytoremediation efforts in grazing lands have prioritized grasses that may be used as forage for cattle. This study investigated the influence of three different forage species—Paspalum notatum, Hemarthria altissima, and Cynodon nlemfuensis—on the loss of phosphorus in leachate from surface soils. The experiment used a nested pot mesocosm design that allowed us to monitor leachate volume and concentration biweekly over the course of 3 months. Pots containing P. notatum plants leached significantly more phosphorus than pots containing C. nlemfuensis or empty pots with no plants growing in them, despite losing an equivalent amount of water. H. altissima lost equivalent amounts of phosphorus in leachate water, but each H. altissima plant removed approximately 33.6 mg of phosphorus, approximately 2.5× that removed by P. notatum (13.4 mg). C. nlemfuensis had lower average leachate phosphorus concentrations at each biweekly sampling than either plant species (C. nlemfuensis‐P. notatum, padj = 0.001; C. nlemfuensis‐H. altissima, padj = 0.02), averaging only 0.110 ppm in leachate relative to 0.175 ppm and 0.200 ppm in pots beneath H. altissima and P. notatum, respectively. This, combined with C. nlemfuensis' slightly higher‐than‐average aboveground P content and overall aboveground biomass expression suggest it is the best possible phytoremediation candidate. As even minor leachate P loads can be critically threatening to neighboring oligotrophic water bodies, if the conservation of downstream environments is the priority, the short‐term threat of increased leachate must be considered. Further research is needed to explore the underlying mechanisms and field‐scale implications of these findings.

Abstract Temperature is commonly acknowledged as one of the primary forces driving ectotherm vector populations, most notably by influencing metabolic rates and survival. Although numerous experiments have shown this for a wide variety of organisms, the vast majority has been conducted at constant temperatures and changes therein, while temperature is far from constant in nature, and includes seasonal and diurnal cycles. As fluctuating temperatures have been described to affect metabolic processes at (sub)cellular level, this calls for studies evaluating the relative importance of temperature fluctuations and the changes therein. To gain insight in the effects of temperature fluctuations on ectotherm development, survival, and sex ratio, we developed an inexpensive, easily reproducible, and open‐source, Arduino‐based temperature control system, which emulates natural sinusoidal fluctuations around the average temperature. We used this novel setup to compare the effects of constant (mean) temperatures, most commonly used in experiments, block schemes, and natural sinusoidal fluctuations as well as an extreme variant with twice its amplitude using the cosmopolitan mosquito species Culex pipiens s.l. as a study organism. Our system accurately replicated the preprogrammed temperature treatments under outdoor conditions, even more accurately than traditional methods. While no effects were detected on survival and sex ratio within the ranges of variation evaluated, development was sped up considerably by including temperature fluctuations, especially during pupation, where development under constant temperatures took almost a week (30%) longer than under natural fluctuations. Doubling the amplitude further decreased development time by 1.5 days. These results highlight the importance of including (natural) oscillations in experiments on ectotherm organisms – both aquatic and terrestrial – that use temperature as a variable. Ultimately, these results have major repercussions for downstream effects at larger scales that may be studied with applications such as ecological niche models, disease risk models, and assessing ecosystem services that rely on ectotherm organisms.

Wildfires in the western US are increasing in frequency, size, and severity. These disturbances alter soil microbiome structure and function, with greater fire severity leading to more pronounced impacts to bacterial, archaeal, and fungal communities. These changes have implications for the provisioning of microbially-mediated ecosystem services (e.g., carbon sequestration, clean water supplies) typically associated with forested watersheds. Challenges in sampling wildfire-impacted areas immediately post-burn have limited our assessment of short-term (i.e., days to weeks) changes in the soil microbiome and understanding of how microbial populations may influence post-fire biogeochemistry and ecosystem recovery. The identification of potential high severity wildfire proxies may help address some of these knowledge gaps. One potential proxy is pile burns scars, which are produced from a set of common techniques for fuel disposal and site preparation in conifer forests throughout the western US and beyond. We sampled depth-resolved layers from fire-impacted soil and combusted litter and woody materials in a series of recent pile burn scars near West Yellowstone, Montana and nearby unburned mineral soil controls to assess whether the pile burn scars exhibited microbial signatures characteristic of forest soils impacted by recent high severity wildfire. Changes in soil carbon and nitrogen chemistry and patterns of microbial alpha and beta diversity broadly aligned with those observed following wildfire, particularly the enrichment of so-called ‘pyrophilous’ taxa. Furthermore, many of the taxa enriched in burned soils likely encoded putative traits that benefit microorganisms colonizing these environments, such as the potential for fast growth or utilization of pyrogenic carbon substrates. We suggest that pile burn scars may represent a useful proxy along the experimental gradient from muffle furnace or pyrocosm studies to largescale prescribed burns in the field to advance understanding of the soil (and related layers, like ash) microbiome following high severity wildfires, particularly when coupled with experimental manipulation. Finally, we discuss existing research gaps that experimentally manipulated pile burns could be utilized to address.

Aquatic ecosystems are often impacted by several human‐derived pressures simultaneously. A key challenge for ecologists is to develop mechanistic understanding of the cumulative effects of multiple stressors on freshwater biodiversity.We established an outdoor mesocosm experiment to examine the individual and combined effects of two key stressors on lake ecosystems globally—nutrient enrichment and amplified water‐level fluctuations—on benthic algal and macroinvertebrate assemblages along a gradient in littoral water depth.We found that nutrient enrichment and water‐level fluctuations not only altered the structure of littoral communities when acting individually, but also interacted to dynamically alter biomass and community structure in different ways at different depths. As expected, enrichment increased benthic algal biomass significantly in very shallow waters. Yet, when enrichment co‐occurred with water‐level fluctuations, this pattern was reversed, with algal biomass increasing significantly in deeper waters, but not in the shallows that were exposed to fluctuating water levels. This pattern occurred across all algal groups that we examined except for green algae. Green algae biomass increased with nutrient enrichment, was greatest in the shallows, and remained unaffected by fluctuating water levels.Water‐level fluctuations modified the functional feeding group structure of benthic macroinvertebrate communities, reducing relative densities of collector‐gatherers and increasing those of predators. However, these changes occurred only in the shallow‐most regions exposed directly to fluctuating water levels.Our results reveal how two globally important stressors of standing water systems can interact in different ways in different ecological contexts and show how stressors can combine to have unanticipated impacts that vary in space. Our findings underscore the potentially highly multifaceted and complex nature of stressor combinations that present a major and growing challenge to ecosystem management, particularly in light of accelerating global environmental change. [ABSTRACT FROM AUTHOR]

Objective: Artificial light at night (ALAN) is one of the most pervasive and rapidly expanding sources of anthropogenic pollution. Aquatic ecosystems may be especially vulnerable to the effects of ALAN due to their disproportionate exposure to anthropogenic pressures. However, research on mechanisms of response to ALAN by aquatic species remains sparse. Our research investigated the extent to which ALAN influences the nocturnal feeding efficiency of Bluegill Lepomis macrochirus. Methods: Using an array of outdoor mesocosm tanks, we assigned juvenile Bluegill to five nighttime lighting treatments (control dark, 1 lx, 4 lx, 12 lx, and intermittent 12 lx). We conducted weekly nighttime feeding trials for 6 weeks to assess four prey capture variables, including capture efficiency (the effectiveness of prey strikes), capture rate (the number of prey items captured), strike rate (the frequency of prey strikes), and latency (time elapsed before the first prey strike). Result: The steady lighting treatments, which were selected based on nighttime urban light intensities we previously measured in the field, had no apparent effect on any of the prey capture variables. However, flashing high‐intensity lights (intended to mimic the effect of passing car headlights on a busy highway) had a significant negative effect on capture rate and strike rate, thereby inhibiting the ability of fish to strike at and capture prey. Conclusion: Our results demonstrate the potential for light pollution (especially flashing or intermittent lights) to interfere with the foraging behavior of this ecologically and economically important sportfish. Impact statementLight pollution, especially flashing lights, may interfere with the foraging behavior of an ecologically and economically important sport fish. [ABSTRACT FROM AUTHOR]

We integrated data from field observations during April and March with data from a 2-week mesocosm experiment to investigate changes in phytoplankton populations in southern Korean coastal waters (KCWs) following nutrient enrichment during early spring of 2021. The mesocosm experiments used 1000 L cylindrical plastic containers that had natural seawater (control), a low nutrient (LN) treatment, or a high nutrient (HN) treatment. The field observations showed that increased freshwater runoff following spring rainfall led to elevated levels of dissolved inorganic nitrogen and silicate and a significant increase in total phytoplankton abundance. In March, nutrient enrichment from water mixing and terrestrial runoff led to dominance of cryptophyte Cryptomonas spp. In April, higher nutrient levels than March (p< 0.05) resulting from increased terrestrial runoff after rainfall and dominant species were Skeletonema spp., and Cryptomonas spp. In the mesocosm experiment, a succession from E. zodiacus initially to Chaetoceros spp. in the middle stage, and then to Cylindrotheca closterium and Pseudo-nitzschia spp. finally was observed, depending on the species-specific nutrient availability after nutrient addition. In principal component analysis, the negative correlation between C. closterium and nutrient levels supports their nutrient availability, which is an adaptation to low-nutrient conditions. The combined data from the field observations and mesocosm experiments indicated that nutrient supplementation from terrestrial runoff and tidal mixing played a crucial role in determining the dynamics of phytoplankton populations during early spring in the KCWs. [ABSTRACT FROM AUTHOR]

Zooplankton are a conduit of energy from autotrophic phytoplankton to higher trophic levels, and they can be a primary point of entry of microplastics into the aquatic food chain. Investigating how zooplankton communities are affected by microplastic pollution is thus a key step toward understanding ecosystem‐level effects of these global and ubiquitous contaminants. Although the number of studies investigating the biological effects of microplastics has grown exponentially in the last decade, the majority have used controlled laboratory experiments to quantify the impacts of microplastics on individual species. Given that all organisms live in multispecies communities in nature, we used an outdoor 1130‐L mesocosm experiment to investigate the effects of microplastic exposure on natural assemblages of zooplankton. We endeavored to simulate an environmentally relevant exposure scenario by manually creating approximately 270 000 0.015 × 1– to 1.5–mm polyester fibers and inoculating mesocosms with zero, low (10 particles/L), and high (50 particles/L) concentrations. We recorded zooplankton abundance and community composition three times throughout the 12‐week study. We found no effect of microplastics on zooplankton abundance, Shannon diversity, or Pielou's evenness. Nonmetric multidimensional scaling plots also revealed no effects of microplastics on zooplankton community composition. Our study provides a necessary and realistic baseline on which future studies can build. Because numerous other stressors faced by zooplankton (e.g., food limitation, eutrophication, warming temperatures, pesticides) are likely to exacerbate the effects of microplastics, we caution against concluding that polyester microfibers will always have no effect on zooplankton communities. Instead, we encourage future studies to investigate the triple threats of habitat degradation, climate warming, and microplastic pollution on zooplankton community health. Environ Toxicol Chem 2024;43:418–428. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Diamide insecticides are widely used in rice paddies and pose a potential threat to aquatic organisms. However, the risk research related to their application in major rice‐producing areas is very limited, especially mesocosm research to simulate the impact on aquatic ecosystems of long‐term exposure, as well as exposure analysis based on local models and local scenarios. To assess potential risks from a novel diamide insecticide (tetrachlorantraniliprole) to aquatic nontarget organisms in the field over long‐term exposure, an outdoor mesocosm study was performed, and the environmental concentrations were predicted by the multimedia paddy‐pond model (TOPRICE). The mesocosm experiment showed that tetrachlorantraniliprole mainly stayed in the aqueous phase after entering the water body. Although the chemical dissipated quickly in the aqueous phase (half‐life of 0.79–1.5 days), it showed toxic effects on zooplankton communities. Cladocerans, represented by Simocephalus vetulus, were most sensitive to tetrachlorantraniliprole stress. Significant short‐term toxicity to cladocerans occurred in all treatment groups, but all recovered within 8 weeks except for the highest concentration group (30.0 µg /L). Based on the ecological recovery results, 7.74 µg tetrachlorantraniliprole/L (nominal concentration, 10.0 µg /L) is suggested to be the no‐observed‐ecological‐adverse‐effect concentration (NOEAEC) for the zooplankton community. When this NOEAEC was compared with predicted environmental concentrations (PECs; the PECs in natural ponds simulated by the TOPRICE model for 148 application scheme combinations in major rice‐producing areas), a relatively high risk of applying tetrachlorantraniliprole during the rice tillering stage was found. The present study makes a positive contribution to the hypothesis that the current Tier 1 approaches for global acute risk assessment have a sufficient protective effect for assessing the risk of tetrachlorantraniliprole to aquatic organisms. Also, the present results should help us to gain a fuller understanding of the ecological risk of diamide insecticides in aquatic ecosystems and their rational application schemes. Environ Toxicol Chem 2024;43:429–439. © 2023 SETAC [ABSTRACT FROM AUTHOR]

Sediment reworking by benthic infauna, namely bioturbation, is of pivotal importance in expansive soft-sediment environments such as the Wadden Sea. Bioturbating fauna facilitate ecosystem functions such as bentho-pelagic coupling and sediment nutrient remineralization capacities. Yet, these benthic fauna are expected to be profoundly affected by current observed rising sea temperatures. In order to predict future changes in ecosystem functioning in soft-sediment environments like the Wadden Sea, knowledge on the underlying processes such as sediment reworking, is crucial. Here, we tested how temperature affects bioturbation and its associated ecosystem processes, such as benthic nutrient fluxes and sediment oxygen consumption, using luminophore tracers and sediment incubation cores. We used a controlled mesocosm experiment set-up with key Wadden Sea benthos species: the burrowing polychaetes Arenicola marina and Hediste diversicolor, the bivalve Cerastoderma edule, and the tube-building polychaete Lanice conchilega. The highest bioturbation rates were observed from A. marina, reaching up to 375 cm²yr-1; followed by H. diversicolor, with 124 cm²yr-1 being the peak bioturbation rate for the ragworm. Additionally, the sediment reworking activity of A. marina facilitated nearly double the amount of silicate efflux compared to any other species. Arenicola marina and H. diversicolor accordingly facilitated stronger nutrient effluxes under a warmer temperature than L. conchilega and C. edule. The oxygen uptake of A. marina and H. diversicolor within the sediment incubation cores was correspondingly enhanced with a higher temperature. Thus, increases in sea temperatures may initially be beneficial to ecosystem functioning in the Wadden Sea as faunal bioturbation is definitely expedited, leading to a tighter coupling between the sediment and overlying water column. The enhanced bioturbation activity, oxygen consumption, and facilitated nutrient effluxes from these invertebrates themselves, will aid in the ongoing high levels of primary productivity and organic matter production. [ABSTRACT FROM AUTHOR]

Lakes worldwide are affected by multiple stressors, including climate change. This includes massive loading of both nutrients and humic substances to lakes during extreme weather events, which also may disrupt thermal stratification. Since multi‐stressor effects vary widely in space and time, their combined ecological impacts remain difficult to predict. Therefore, we combined two consecutive large enclosure experiments with a comprehensive time‐series and a broad‐scale field survey to unravel the combined effects of storm‐induced lake browning, nutrient enrichment and deep mixing on phytoplankton communities, focusing particularly on potentially toxic cyanobacterial blooms. The experimental results revealed that browning counteracted the stimulating effect of nutrients on phytoplankton and caused a shift from phototrophic cyanobacteria and chlorophytes to mixotrophic cryptophytes. Light limitation by browning was identified as the likely mechanism underlying this response. Deep‐mixing increased microcystin concentrations in clear nutrient‐enriched enclosures, caused by upwelling of a metalimnetic Planktothrix rubescens population. Monitoring data from a 25‐year time‐series of a eutrophic lake and from 588 northern European lakes corroborate the experimental results: Browning suppresses cyanobacteria in terms of both biovolume and proportion of the total phytoplankton biovolume. Both the experimental and observational results indicated a lower total phosphorus threshold for cyanobacterial bloom development in clearwater lakes (10–20 μg P L−1) than in humic lakes (20–30 μg P L−1). This finding provides management guidance for lakes receiving more nutrients and humic substances due to more frequent extreme weather events. [ABSTRACT FROM AUTHOR]

Decomposer fungi play a fundamental role in terrestrial ecosystem dynamics. In the southwestern United States, climate change is causing more frequent and severe droughts, which may alter fungal community composition and activity. Investigating relationships between fungal traits may improve the prediction of fungal responses to drought. In this dual field and laboratory experiment, we examine whether trade-offs occur between traits associated with drought. Specifically, we test the hypothesis that fungi sort into lifestyles specializing in growth yield, resource acquisition, and drought stress tolerance (“YAS” framework). For the field experiment, we constructed microbial “cages” containing sterilized litter and 1 of 10 fungal isolates. These cages were placed in long-term drought and control plots in a southern Californian grassland for 6 and 12 months. We measured fungal hyphal length per unit litter mass loss for growth yield, the potential activities of four extracellular enzymes for resource acquisition, and the ability to grow in the drought versus control plots for drought stress tolerance. We compared these results with a laboratory microcosm experiment constructed with the same fungal isolates and that measured the same fungal traits. The field experiment corroborated our laboratory results, in that no trade-offs were observed between growth yield and resource acquisition traits. However, in contrast to the laboratory experiment, drought tolerance was negatively related to extracellular enzyme activity and growth yield in the field, implying a trade-off. Despite this observed trade-off in the field, growth yield was not hindered by drought. We propose a modification to the YAS framework, by combining the growth yield and resource acquisition lifestyles, which may be more appropriate for this arid system. This joint laboratory and field approach contextualizes a theoretical framework in microbial ecology and improves understanding of fungal community response to climate change.

Marine stock enhancement is not only commonly reported to amplify the target species production but also induces some potential threats or effects at multiple ecological levels in the receiving ecosystem. Studies on the interaction between released and naturally occurring organisms are necessary to avoid or minimize the adverse impacts of invasive species from stock enhancement in the receiving system. Chinese shrimp Fenneropenaeus chinensis, are an important stock enhancement species, and in recent years approximately 10 billion have been released annually into the coastal waters of China. Owing to fishing pressure and the ecological complexity of the open sea, the interaction between the released shrimp and native species may be weak and undetectable. Studies on the ecological impacts of such intensive releasing activities are limited. Therefore, in this study, an in-situ mesocosm experiment was carried out to determine if the released shrimp altered the relative composition and niche characteristics of fish, the results of which could serve as a reference to the local risk management of the species stock enhancement. The mesocosm was located in the shrimp-releasing channel of Weihe, Laizhou Bay, from April to September 2019. A cross design of four treatments with three replicates was conducted in the mesocosm. The habitats were homogenized across the replicates by mixing substrates and filtering seawater with a 0.28 cm sieve. The number of individual shrimp larvae released into net enclosures in each of the four treatments were: A) 2 400, B) 1 800, C) 1 200, and O) 0. The treatments were designed to represent the release of 1 billion, 750 million, 500 million, and no shrimp larvae (none-releasing) in the coastal waters of Laizhou Bay, respectively. The released shrimp larvae had an average body length of (1.63±0.18) cm and an average body width of (0.38±0.12) cm. At the end of the experimental period in September, shrimp and fishes were recaptured and their Levin's niche breadth and overlap indices were examined in each enclosure. Results indicated that within the enclosures of the four treatments, the recapture rates of shrimp ranged from 8.16% to 12.69% and had an average value of 9.87%. The number of recaptured shrimp increased with the number released, and had the highest value in enclosure A. However, the total biomass, average individual mass, and recapture rate of shrimp did not show a similar pattern among enclosures. The recapture rate of shrimp was significantly different among the treatments and had the highest value in enclosure C. The fish species composition was similar across all four treatment enclosures and included six species with three different feeding habits: Omnivores (Konosirus punctatus and Liza haematocheila), zooplanktivores (Thryssa mystax and Sardinella zunasi), and fish/shrimp predators (carnivores) (Acanthogobius sp. and Sparus microcephalus czerskii). Of the fish species, Acanthogobius sp. dominated in all enclosures, while S. m. czerskii occurred in only a few. There was no significant difference in the number and biomass of total fishes and carnivorous fishes among enclosures. There were more omnivorous fishes in the released enclosures A–C, while the number of zooplanktivorous fishes decreased when shrimp were released and had the highest number and biomass in the non-released enclosure O. Moreover, fishes with different feeding habits had variable niche breadths among the four treatment enclosures. Most fish species had a wider niche breadth in enclosures with released shrimp (enclosure A–C) than in enclosure O. Both the fish´s niche overlap indices and the species pairs with high niche overlap (> 0.75) decreased in the order non-released enclosure O > released enclosure B > enclosure C > enclosure A. The carnivorous fish Acanthogobius sp. had more pairs with niche overlap indices (> 0.75) in the non-released enclosure O than in the other three treatments. A similarity analysis and multidimensional plot indicated that enclosures A and O could be differentiated by the relatively long similarity distance and little overlap area. The results of the experiment suggest that the shrimp recapture efficiency did not increase when shrimp were released. In the waters of the study area, released shrimp could have a positive effect on the total output of both shrimp and fish, especially for omnivorous and carnivorous fishes, as the shrimp could share predation pressure and provide food for them. In addition, the shrimp release may affect the relative composition and niche characteristics of fish by increasing their niche breadth and reducing the overlap between fishes with different feeding habits, and the impacts may be more detectable as the shrimp number increases.

When cyanobacterial phytoplankton form harmful cyanobacterial blooms (HCBs), the toxins they produce threaten freshwater ecosystems. Hydrogen peroxide is often used to control HCBs, but it is broadly toxic and dangerous to handle. Previously, we demonstrated that glucose addition to lake water could suppress the abundance of cyanobacteria. In this study, glucose was compared to hydrogen peroxide for the treatment of cyanobacterial phytoplankton communities. The six-week study was conducted in the large mesocosms facility at Grand Valley State University’s Annis Water Resources Institute in Michigan. To 1000 L of Muskegon Lake water, glucose was added at either 150 mg or 30 mg glucose/L. Hydrogen peroxide was added at 3 mg/L to two 1000 L mesocosms. And two mesocosms were left untreated as controls. Triplicate 100 mL samples were collected weekly from each mesocosm, which were then filtered and frozen at −80 °C for 16S rRNA amplicon sequencing. The 16S rRNA amplicon sequencing results revealed that hydrogen peroxide treatment quickly reduced the relative abundance of the cyanobacteria compared to the control mesocosms, but the cyanobacteria population returned over the course of the 6-week study. On the other hand, both glucose concentrations caused a rapid proliferation of multiple low abundance proteobacterial and bacteroidotal taxa resulting in notable increases in taxonomic richness over the duration of the study and reducing the relative abundance of cyanobacteria. Although hydrogen peroxide quickly suppressed the cyanobacteria, the population later returned to near starting levels. The glucose suppressed the cyanobacterial phytoplankton apparently by promoting competitive heterotrophic bacteria.

Abstract Environmental DNA (eDNA) holds notable potential for biomonitoring and ecological research. However, its utility for quantifying temporal changes in abundance, biomass, and diversity remains contentious. We investigated biotic and abiotic factors influencing temporal variation in eDNA concentration in large, 28,000 L experimental mesocosms. Time series data demonstrated a positive relationship between the population abundance and biomass of the Cladoceran zooplankton species Daphnia magna and eDNA concentration, with a time lag of ~3.5 days in 25°C conditions, and up to 28 days in 15°C. Water temperature variations within mesocosms did not consistently influence eDNA quantity, although water temperature negatively predicted DNA concentration across mesocosms. Algal density negatively correlated with D. magna eDNA quantity across and within mesocosms. We demonstrate that eDNA signal detection can be used as a proxy for relative abundance and suggest that future investigation into the dynamics of eDNA shedding and degradation processes is warranted.

Abstract Proteinase K (ProK) is regarded as an essential ingredient in most DNA extraction protocols for protein‐rich sample types such as tissue, blood, and mucus. However, ProK is expensive and may be unnecessary when samples are protein‐limited, such as environmental DNA (eDNA) from oligotrophic seawater. To investigate this, we filtered seawater through Sterivex cartridges from a mesocosm receiving input from the adjacent coral reef slope at the Hawai‘i Institute of Marine Biology. We tested whether the addition of varying levels of ProK (0 μL, 25 μL, 50 μL, 100 μL, or 150 μL—20 mg/mL stock concentrations) to 1.8 mL of lysis buffer affected DNA yield and the diversity, community composition, and detection of known organisms within the mesocosm community based on zero‐width operational taxonomic units (ZOTUs) obtained from DNA metabarcoding. We found no significant differences in diversity metrics among ProK quantities and dominant ZOTUs were consistent across concentrations. Over 50% of detected ZOTUs were shared among samples and only two ZOTUs were unique to samples of a particular ProK concentration. While the community composition among ProK quantities differed, pairwise community comparisons between quantities were not statistically significant and matched the known species composition of the mesocosm. These results suggest that rare ZOTUs and eDNA patchiness are driving overall community differences as opposed to extraction ingredients. Our data show that ProK is not essential when assessing communities from oligotrophic marine environments using eDNA and that the reduction or elimination of ProK can decrease sample preparation time and costs while maintaining data integrity.

Sediment reworking by benthic infauna, namely bioturbation, is of pivotal importance in expansive soft-sediment environments such as the Wadden Sea. Bioturbating fauna facilitate ecosystem functions such as bentho-pelagic coupling and sediment nutrient remineralization capacities. Yet, these benthic fauna are expected to be profoundly affected by current observed rising sea temperatures. In order to predict future changes in ecosystem functioning in soft-sediment environments like the Wadden Sea, knowledge on the underlying processes such as sediment reworking, is crucial. Here, we tested how temperature affects bioturbation and its associated ecosystem processes, such as benthic nutrient fluxes and sediment oxygen consumption, using luminophore tracers and sediment incubation cores. We used a controlled mesocosm experiment set-up with key Wadden Sea benthos species: the burrowing polychaetes Arenicola marina and Hediste diversicolor, the bivalve Cerastoderma edule, and the tube-building polychaete Lanice conchilega. The highest bioturbation rates were observed from A. marina, reaching up to 375 cm2yr−1; followed by H. diversicolor, with 124 cm2yr−1 being the peak bioturbation rate for the ragworm. Additionally, the sediment reworking activity of A. marina facilitated nearly double the amount of silicate efflux compared to any other species. Arenicola marina and H. diversicolor accordingly facilitated stronger nutrient effluxes under a warmer temperature than L. conchilega and C. edule. The oxygen uptake of A. marina and H. diversicolor within the sediment incubation cores was correspondingly enhanced with a higher temperature. Thus, increases in sea temperatures may initially be beneficial to ecosystem functioning in the Wadden Sea as faunal bioturbation is definitely expedited, leading to a tighter coupling between the sediment and overlying water column. The enhanced bioturbation activity, oxygen consumption, and facilitated nutrient effluxes from these invertebrates themselves, will aid in the ongoing high levels of primary productivity and organic matter production.

Introduction: Microbes are increasingly (re)considered for environmental assessments because they are powerful indicators for the health of ecosystems. The complexity of microbial communities necessitates powerful novel tools to derive conclusions for environmental decision-makers, and machine learning is a promising option in that context. While amplicon sequencing is typically applied to assess microbial communities, metagenomics and total RNA sequencing (herein summarized as omics-based methods) can provide a more holistic picture of microbial biodiversity at sufficient sequencing depths. Despite this advantage, amplicon sequencing and omics-based methods have not yet been compared for taxonomy-based environmental assessments with machine learning. Methods: In this study, we applied 16S and ITS-2 sequencing, metagenomics, and total RNA sequencing to samples from a stream mesocosm experiment that investigated the impacts of two aquatic stressors, insecticide and increased fine sediment deposition, on stream biodiversity. We processed the data using similarity clustering and denoising (only applicable to amplicon sequencing) as well as multiple taxonomic levels, data types, feature selection, and machine learning algorithms and evaluated the stressor prediction performance of each generated model for a total of 1,536 evaluated combinations of taxonomic datasets and data-processing methods. Results: Sequencing and data-processing methods had a substantial impact on stressor prediction. While omics-based methods detected a higher diversity of taxa than amplicon sequencing, 16S sequencing outperformed all other sequencing methods in terms of stressor prediction based on the Matthews Correlation Coefficient. However, even the highest observed performance for 16S sequencing was still only moderate. Omics-based methods performed poorly overall, but this was likely due to insufficient sequencing depth. Data types had no impact on performance while feature selection significantly improved performance for omicsbased methods but not for amplicon sequencing. Discussion: We conclude that amplicon sequencing might be a better candidate for machine-learning-based environmental stressor prediction than omics-based methods, but the latter require further research at higher sequencing depths to confirm this conclusion. More sampling could improve stressor prediction performance, and while this was not possible in the context of our study, thousands of sampling sites are monitored for routine environmental assessments, providing an ideal framework to further refine the approach for possible implementation in environmental diagnostics. [ABSTRACT FROM AUTHOR]

Background: During a study on the outdoor floating leaf blade production of Nymphoides peltata (S.G. Gmel.) O. Kuntze (Fringed Water Lily), initial leaf blade decomposition was studied by simultaneously measuring infected, damaged and lost area of floating leaf blades. Methods: Data on initial decomposition over time were collected for all leaves during one growth season in four plots: two in outdoor mesocosms and two in an oxbow lake. Each leaf was tagged uniquely upon appearance in a plot. The vegetation in the mesocosms differed with respect to plant species, one contained a monoculture of N. peltata and the other N. peltata associated with Glyceria fluitans (L.) R. Br. and G. maxima (Hartm.) Holmb. The lake plots were situated within a monospecific N. peltata stand, differing in depth and position within the stand. Leaf length, visually estimated percentages of damaged area for each damage type, and decay of the tagged leaves were recorded bi-weekly. When the leaf blades sunk under the water surface or disappeared completely, they were no longer followed. Under water the leaves decayed and were consumed by snails completely, so contributing to the detritus food chain. Results: The observed causes of damage on floating leaves were consumption and/or damage by waterbirds (Fulica atra), pond snails, caterpillars (Elophila nymphaeata, Cataclysta lemnata), chironomid larvae (Cricotopus trifasciatus), infection by a phytopathogenic fungus (Septoria villarsiae), senescence by autolysis, and microbial decay. Successional changes in causes of leaf decomposition and impacts of different causes are discussed. [ABSTRACT FROM AUTHOR]

Even though graphene-family materials (GFMs) hold great promise for various applications, there are still significant knowledge gaps in ecotoxicology and environmental risk assessment associated with their potential environmental impacts. Here, we provide a critical perspective on published ecotoxicity studies of GFMs based on meticulous bibliometric research. Based on the results of our review paper, in order to fill in the current critical knowledge gaps, the following issues are recommended for consideration: performing more studies on GFMs' effects at environmentally relevant concentrations and more field and laboratory studies with marine and terrestrial organisms. It is also recommended to assess the ecotoxicity of GFMs in more environmentally relevant conditions, such as in trophic chain transfer studies and by multispecies exposure in micro- or mesocosms, as well as gaining insights into the interactive effects between GFMs and environmental pollutants. It was also revealed that despite their widespread detection in different environmental compartments the potential impacts of GFMs in complex test systems where hierarchical trophic organisation or trophic transfer studies are significantly under-represented. One of the main causes was identified as the difficulties in the physicochemical characterisation of GFMs in complex terrestrial test systems or aquatic micro- and mesocosm studies containing a sediment phase. The lack of tools for adequate characterisation of GFMs in these complex test systems may discourage researchers from conducting experiments under environmentally relevant test conditions. In the coming years, fundamental research about these complex test systems will continue to better understand the mechanism behind GFM toxicity affecting organisms in different environmental compartments and to ensure their safe and sustainable use in the future. [ABSTRACT FROM AUTHOR]

Anthropogenic pollutants, such as excessive nutrients and marine plastic debris (MPDs), can significantly affect marine micro-ecosystems, including phytoplankton and periphyton. However, there have been few studies about the impacts of these pollutants on microalgal community. We aimed to assess these impacts by 1000-L mesocosm experiments that simulated the influx of nutrients and MPDs in autumn (natural seawater: control, low nutrient: LN group, high nutrient: HN group). The phytoplankton biomass in water increased rapidly in the LN group (maximum 21.7 μg L−1) and HN group (maximum 14.6 μg L−1), resulting in a succession from Cryptomonas spp. to Pseudo-nitzschia spp.. Interestingly, although the threefold difference in nutrient addition between the LN and HN groups, the phytoplankton biomass was similar (cumulative biomass during the entire experiment: 68.9 μg L−1 in LN group and 70.7 μg L−1 in HN group). On the other hand, on day 15 the periphyton biomass on the PP plates was 12.7-times higher in HN group than in LN group. Also, the estimated periphyton biomass of mesocosm wall was significantly different between LN group (4,696 µg cm−2) and HN group (59,835 µg cm−2), in relation to the lack of phytoplankton biomass relative to nutrient addition. In particular, the species-specific characteristics of Cylindrotheca closterium, which grow well even in low nutrients, and the relatively weak solar irradiance in autumn helped to increase the periphyton biomass. Therefore, these findings suggest that the influx of MPDs and nutrients can change the community structure of microalgae, leading to an increase in the periphyton ratio, and this change can have negative consequences on the marine ecosystem by potentially reducing primary productivity. Our mesocosm experiments provide important ecological insights regarding the time-series changes of phytoplankton in the water column and of microalgae attached to MPD when nutrients and plastic debris are introduced into coastal waters through river discharge after rainfall during autumn in temperate regions. [ABSTRACT FROM AUTHOR]

Decline in species richness as well as changes in community evenness or functional diversity have been hypothesised to jointly affect ecosystem functioning. However, disentangling the relative effects of these changes in community structure is hard as these different aspects often covary with species richness in real‐world ecosystems. In this study, we investigated the individual and interactive effects of functional diversity and community evenness of predators on the level of control of herbivorous prey.Using a highly replicated mesocosm experiment, we crossed three levels of functional diversity of arthropod predators with two levels of community evenness while controlling for the effect of species richness. Using this experimental setting, we hypothesised that the effect size of functional diversity of predators depends on community evenness. We expected a positive effect of functional diversity of predators on top‐down control at high level of community evenness while we thought that species identity and their associated traits should drive most of the effect on top‐down control at low level of community evenness.Our results did not provide any evidence for an interaction between functional diversity and community evenness nor any beneficial effect of increased functional diversity overall on predation rates of herbivorous prey. In addition, our results revealed that species and functional identity drives most of the effects of predator community composition on top‐down control of their prey in our study system. Assemblages composed of active hunters with low handling time and no starvation ability tended to have the highest impacts on prey biomass.By indicating that top‐down control of herbivorous prey by arthropod predators is mainly driven by species and functional identity and not by functional diversity, our study provides insights into the consequences of ongoing species loss on ecosystem functioning. Future research should now explore the predictability of trophic interactions based on functional traits of predator and herbivorous prey to anticipate the consequences of changes in species composition on ecosystem functioning. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Exposure to pesticides can profoundly alter community dynamics. It is expected that dominance patterns will be enhanced or reduced depending on whether the dominant species is less or more sensitive to the pesticide than the subdominant species. Community dynamics are, however, also determined by processes linked to population growth as well as competition at carrying capacity. Here, we used a mesocosm experiment to quantify the effect of chlorpyrifos exposure on the population dynamics of four cladoceran species (Daphnia magna, Daphnia pulicaria, Daphnia galeata and Scapholeberis mucronata) in mixed cultures, testing for direct effects of chlorpyrifos and indirect effects mediated by interactions with other species on the timing of population growth and dominance at carrying capacity. We also quantified whether the pesticide‐induced changes in community dynamics affected top‐down control of phytoplankton. By adding a treatment in which we used different genotype combinations of each species, we also tested to what extent genetic composition affects community responses to pesticide exposure. Immobilization tests showed that D. magna is the least sensitive to chlorpyrifos of the tested species. Chlorpyrifos exposure first leads to a reduction in the abundance of D. galeata to the benefit of D. pulicaria, and subsequently to a reduction in densities of D. pulicaria to the benefit of D. magna. This resulted in D. magna being more dominant in the pesticide than in the control treatment by the end of the experiment. There was no effect of genotypic differences on community patterns, and top‐down control of phytoplankton was high in all treatments. Our results suggest that in this community dominance patterns are enhanced in line with the observed among‐species differences in sensitivity to the pesticide. Our results also show that the development of the community in pesticide treatment is a complex interaction between direct and indirect effects of the pesticide. [ABSTRACT FROM AUTHOR]

Microbial communities are essential components of aquatic ecosystems and are widely employed for the detection, protection, and restoration of water ecosystems. The polyurethane foam unit (PFU) method, an effective and widely used environmental monitoring technique, has been improved with the eDNA-PFU method, offering efficiency, rapidity, and standardization advantages. This research aimed to explore the colonization process of microbial communities within PFUs using eDNA-PFU technology. To achieve this, we conducted ten-day monitoring and sequencing of microbial communities within PFUs in a stable and controlled artificial aquatic ecosystem, comparing them with water environmental samples (eDNA samples). Results showed 1065 genera in eDNA-PFU and 1059 in eDNA, with eDNA-PFU detecting 99.95% of eDNA-identified species. Additionally, the diversity indices of bacteria and eukaryotes in both methods showed similar trends over time in the colonization process; however, relative abundance differed. We further analyzed the colonization dynamics of microbes in eDNA-PFU and identified four clusters with varying colonization speeds. Notably, we found differences in colonization rates between bacteria and eukaryotes. Furthermore, the Molecular Ecological Networks (MEN) showed that the network in eDNA-PFU was more modular, forming a unique microbial community differentiated from the aquatic environment. In conclusion, this study, using eDNA-PFU, comprehensively explored microbial colonization and interrelationships in a controlled mesocosm system, providing foundational data and reference standards for its application in aquatic ecosystem monitoring and beyond. [ABSTRACT FROM AUTHOR]

The microbial composition of the rhizosphere and greenhouse gas (GHG) emissions under the most common input combinations in maize (Zea mays L.) cultivated in Brazil have not been characterized yet. In this study, we evaluated the influence of maize stover coverage (S), urea-topdressing fertilization (F), and the microbial inoculant Azospirillum brasilense (I) on soil GHG emissions and rhizosphere microbial communities during maize development. We conducted a greenhouse experiment and measured methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) fluxes from soil cultivated with maize plants under factorial combinations of the inputs and a control treatment (F, I, S, FI, FS, IS, FIS, and control). Plant biomass was evaluated, and rhizosphere soil samples were collected at V5 and V15 stages and DNA was extracted. The abundance of functional genes (mcrA, pmoA, nifH, and nosZ) was determined by quantitative PCR (qPCR) and the structure of the microbial community was assessed through 16S rRNA amplicon sequencing. Our results corroborate with previous studies which used fewer input combinations and revealed different responses for the following three inputs: F increased N2O emissions around 1 week after application; I tended to reduce CH4 and CO2 emissions, acting as a plant growth stimulator through phytohormones; S showed an increment for CO2 emissions by increasing carbon-use efficiency. IS and FIS treatments presented significant gains in biomass that could be related to Actinobacteria (19.0%) and Bacilli (10.0%) in IS, and Bacilli (9.7%) in FIS, which are the microbial taxa commonly associated with lignocellulose degradation. Comparing all factors, the IS (inoculant + maize stover) treatment was considered the best option for plant biomass production and GHG mitigation since FIS provides small gains toward the management effort of F application.