Effects Of Multiple Stressors Research Articles

Population origin and heritable effects mediate road salt toxicity and thermal stress in an amphibian

Human impacts on wild populations are numerous and extensive, degrading habitats and causing population declines across taxa. Though these impacts are often studied individually, wild populations typically face suites of stressors acting concomitantly, compromising the fitness of individuals and populations in ways poorly understood and not easily predicted by the effects of any single stressor. Developing understanding of the effects of multiple stressors and their potential interactions remains a critical challenge in environmental biology. Here, we focus on assessing the impacts of two prominent stressors associated with anthropogenic activities that affect many organisms across the planet – elevated salinity (e.g., from road de-icing salt) and temperature (e.g. from climate change). We examined a suite of physiological traits and components of fitness across populations of wood frogs originating from ponds that differ in their proximity to roads and thus their legacy of exposure to pollution from road salt. When experimentally exposed to road salt, wood frogs showed reduced survival (especially those from ponds adjacent to roads), divergent developmental rates, and reduced longevity. Family level effects mediated these outcomes, but high salinity generally eroded family level variance. When combined, exposure to both temperature and salt resulted in very low survival, and this effect was strongest in roadside populations. Taken together, these results suggest that temperature is an important stressor capable of exacerbating impacts from a prominent contaminant confronting many freshwater organisms in salinized habitats. More broadly, it appears likely that toxicity might often be underestimated in the absence of multi-stressor approaches.

Effects of multiple stressors on freshwater food webs: Evidence from a mesocosm experiment

Natural and anthropogenic pressures exert influence on ecosystem structure and function by affecting the physiology and behavior of organisms, as well as the trophic interactions within assemblages. Therefore, understanding how multiple stressors affect aquatic ecosystems can improve our ability to manage and protect these ecosystems and contribute to understanding fundamental ecological principles. Here, we conducted a mesocosm experiment to ascertain the individual and combined effects of multiple stressors on trophic interactions within species in freshwater ecosystems. Furthermore, we investigated how species respond to such changes by adapting their food resources. To mimic a realistic food web, we selected fish and shrimp as top predators, gastropods, zooplankton and zoobenthos as intermediate consumers, with producers (macrophytes, periphyton and phytoplankton) and detritus as basal resources. Twelve different treatments included a control, nutrient loading only, herbicide exposure only, and a combination of nutrient loading and herbicide exposure, each replicated under ambient temperature, constant warming and multiple heat waves to simulate environmental stressors. Our results demonstrated that antagonistic interactions between environmental stressors were widespread in trophic interactions, with a more pronounced and less intense impact observed for the high trophic level species. The responses of freshwater communities to environmental stressors are complex, involving direct effects on individual species as well as indirect effects through species interactions. Moreover, our results confirmed that the combinations of stressors, but not individual stressors, led to a shift to herbivory in top predators, indicating that multiple stressors can be more detrimental to organisms than individual stressors alone. These findings elucidate how changes in the resource utilization of species induced by environmental stressors can potentially influence species interactions and the structural dynamics of food webs in freshwater ecosystems.

Disentangling effects of multiple agricultural stressors on benthic and hyporheic nitrate uptake

Agricultural land use alters nitrate (NO3–) uptake dynamics in streams, but the specific mechanisms linking individual agricultural stressors to benthic and hyporheic uptake remain unclear. Using stream-side mesocosms and 15N-nitrate additions, we examined the individual and combined effects of fine sediment (FS) and augmented light and phosphorus levels (L&P) on benthic and hyporheic NO3– uptake rates. In absence of FS, L&P stimulated uptake of autotrophic and heterotrophic biofilms, leading to a 12- and 7-fold increase in the benthic and hyporheic compartments, respectively. Under ambient light and nutrient conditions, FS reduced by 3-fold benthic uptake, but effects were not significant. Conversely, in the hyporheic compartment, FS induced anoxic conditions, likely stimulating denitrification and causing a 14-fold increase in hyporheic uptake. When these stressors were combined, they did not interact in the benthic compartment. Conversely, in the hyporheic compartment they interacted antagonistically, with L&P diminishing the increase in uptake induced by FS. Our results indicate that the previously observed increase of whole-stream NO3– uptake in agricultural streams is attributable to nutrients and light stimulating benthic uptake, while fine sediment effects and the role of the hyporheic compartment to total uptake are modest. Moreover, the finding that stressor interactions vary with ecosystem compartments calls for a consideration of all compartments and their contribution to whole-system functioning in multiple stressor studies. We are beginning to understand how multiple interacting stressors affect stream functioning, but more mechanistic evidence is needed to disentangle whether additive or non-additive effects prevail in human-altered ecosystems.

Water‐level fluctuations and nutrient enrichment interact to alter ecosystem structure in distinct ways at different water depths

Abstract 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.

Are fish immunocompetent enough to face climate change?

Ongoing climate change has already been associated with increased disease outbreaks in wild and farmed fish. Here, we evaluate the current knowledge of climate change-related ecoimmunology in teleosts with a focus on temperature, hypoxia, salinity and acidification before exploring interactive effects of multiple stressors. Our literature review reveals that acute and chronic changes in temperature and dissolved oxygen can compromise fish immunity which can lead to increased disease susceptibility. Moreover, temperature and hypoxia have already been shown to enhance the infectivity of certain pathogens/parasites and to accelerate disease progression. Too few studies exist that have focussed on acidification, but direct immune effects seem to be limited while salinity studies have led to contrasting results. Likewise, multi-stressor experiments essential for unravelling the interactions of simultaneously changing environmental factors are still scarce. This ultimately impedes our ability to estimate to what extent climate change will hamper fish immunity. Our review about epigenetic regulation mechanisms highlights the acclimation potential of the fish immune response to changing environments. However, due to the limited number of epigenetic studies, overarching conclusions cannot be drawn. Finally, we provide an outlook on how to better estimate the effects of realistic climate change scenarios in future immune studies in fish.

Fine sediment and the insecticide chlorantraniliprole inhibit organic‐matter decomposition in streams through different pathways

Abstract Intensive agriculture drives an ongoing deterioration of stream biodiversity and ecosystem functioning across the planet. Key agricultural stressors include increased deposited fine sediment and insecticides flushed from adjacent land into streams. The individual and combined effects on aquatic biota are increasingly studied, but the functional consequences of biodiversity loss associated with agricultural stressors remain poorly understood. We addressed this knowledge gap by examining the effects of fine sediment and different concentrations of the insecticide chlorantraniliprole on organic‐matter decomposition. We conducted an outdoor stream mesocosm experiment. Mesocosms contained a standardised organic‐matter assay (the cotton‐strip assay), which was used to assess organic‐matter decomposition rates (as tensile‐strength loss of the fabric) and microbial respiration of the cotton strips. The decomposition rate of strips buried under fine sediment was inhibited, a result we attribute to the limited accessibility for invertebrate feeding and microbial activities, as well as the limited nutrient and dissolved oxygen exchange. The insecticide also inhibited decay rates, a finding we relate to reduced invertebrate grazing and associated excessive algal growth. In contrast to decomposition rates, we did not observe stressor effects on microbial respiration. An interaction between fine sediment and chlorantraniliprole was not identified. Our results suggest that stressors induced by agriculture affect functions of stream ecosystems through a variety of pathways and operate by modifying habitats and biotic interactions. By examining a combination of stressors and responses that have not been addressed before, this study gives important insights into the effects of agricultural practices on streams. Understanding the effects of chlorantraniliprole is especially important since it is likely to become more widely used in future agricultural practice due to the increasing ban on neonicotinoid insecticides. Furthermore, most experimental studies address multiple stressor effects on biota. For a comprehensive understanding of complex stressor effects on ecosystems, ecosystem functions also need to be studied, such as the organic‐matter decomposition within streams.

Ameliorating the effects of multiple stresses on agronomic traits in crops: modern biotechnological and omics approaches

Ameliorating the effects of multiple stresses on agronomic traits in crops: modern biotechnological and omics approaches

Effects of Multiple Environmental Stressors on Zoobenthos Communities in Shallow Lakes: Evidence from a Mesocosm Experiment

Multiple stressors, including climate change, eutrophication, and pesticide contamination, are significant drivers of the decline in lake zoobenthos. Zoobenthos play a crucial role in aquatic ecosystems, impacting energy dynamics, nutrient cycling, and sediment degradation. However, these stressors have led to a decrease in the abundance and diversity of zoobenthos, resulting in notable changes in species composition and structure. Eutrophication typically increases zoobenthos abundance while reducing taxonomic diversity. Climate change, such as warming and heatwaves, also affects the zoobenthos community structure, with different species exhibiting varying levels of adaptability to temperature changes. Additionally, pesticides like imidacloprid have negative effects on the survival and growth of zoobenthos. However, the interactions between imidacloprid and other stressors remain understudied. Here, we used 48 mesocosms (2500 L) to simulate shallow lakes. We combined nutrient loading, sustained warming, and the imidacloprid pesticide to test how these stressors interactively influence the survival and community of zoobenthos. The experimental results demonstrate that elevated temperatures have a significant impact on aquatic benthic organisms under different treatment conditions. The increase in temperature led to a notable rise in species richness and α-diversity, primarily attributed to the stimulation of metabolic activities in zoobenthos, promoting their growth and reproduction. This finding underscores the potential influence of climate change on aquatic benthic ecosystems, particularly in terms of its promoting effect on α-diversity. However, it is essential to note that elevated temperatures also reduced β-diversity among different sites, implying a potential trend toward homogenization in zoobenthos communities under warmer conditions. Moreover, this study revealed the interactive effects of multiple stressors on the diversity of aquatic benthic communities. Specifically, the pesticide imidacloprid’s impact on zoobenthos is not isolated but demonstrates complex effects within various treatment interactions. In the presence of both temperature elevation and the addition of imidacloprid, the presence of imidacloprid appears to counteract the adverse effects of temperature elevation, resulting in increased species diversity. However, when imidacloprid coincides with nutrient input, it significantly affects α-diversity negatively. These findings highlight the complexity of zoobenthos responses to multiple stressors and how these factors influence both α-diversity and β-diversity. They provide valuable insights for further research on the conservation and management of ecosystems.

Dust storms increase the tolerance of phytoplankton to thermal and pH changes.

Aquatic communities are increasingly subjected to multiple stressors through global change, including warming, pH shifts, and elevated nutrient concentrations. These stressors often surpass species tolerance range, leading to unpredictable consequences for aquatic communities and ecosystem functioning. Phytoplankton, as the foundation of the aquatic food web, play a crucial role in controlling water quality and the transfer of nutrients and energy to higher trophic levels. Despite the significance in understanding the effect of multiple stressors, further research is required to explore the combined impact of multiple stressors on phytoplankton. In this study, we used a combination of crossed experiment and mechanistic model to analyze the ecological and biogeochemical effects of global change on aquatic ecosystems and to forecast phytoplankton dynamics. We examined the effect of dust (0-75 mg L-1 ), temperature (19-27°C), and pH (6.3-7.3) on the growth rate of the algal species Scenedesmus obliquus. Furthermore, we carried out a geospatial analysis to identify regions of the planet where aquatic systems could be most affected by atmospheric dust deposition. Our mechanistic model and our empirical data show that dust exerts a positive effect on phytoplankton growth rate, broadening its thermal and pH tolerance range. Finally, our geospatial analysis identifies several high-risk areas including the highlands of the Tibetan Plateau, western United States, South America, central and southern Africa, central Australia as well as the Mediterranean region where dust-induced changes are expected to have the greatest impacts. Overall, our study shows that increasing dust storms associated with a more arid climate and land degradation can reverse the negative effects of high temperatures and low pH on phytoplankton growth, affecting the biogeochemistry of aquatic ecosystems and their role in the cycles of the elements and tolerance to global change.

Effects of flow reduction and artificial light at night (ALAN) on litter decomposition and invertebrate communities in streams: A flume experiment

River ecosystems are heavily impacted by multiple stressors, where effects can cascade downstream of point sources. However, a spatial approach to assess the effects of multiple stressors is missing. We assessed the local and downstream effects on litter decomposition, and associated invertebrate communities of two stressors: flow reduction and artificial light at night (ALAN). We used an 18-flow-through mesocosm system consisting of two tributaries, where we applied the stressors, merging in a downstream section. We assessed the changes in decomposition rate and invertebrate community structure in leaf bags. We found no effect of ALAN or its interaction with flow reduction on the litter decomposition or the invertebrate community in the tributaries. Flow reduction alone led to a 14.8 % reduction in decomposition rate in the tributaries. We recorded no effect of flow reduction on the macroinvertebrates community composition in the litter bags. We also observed no effects of the spatial arrangement of the stressors on the litter decomposition and macroinvertebrate community structure downstream. Overall, our results suggest the impact of stressors on litter decomposition and macroinvertebrate communities remained local in our experiment. Our work thus calls for further studies to identify the mechanisms and the conditions under which spatial effects dominate over local processes.

Emergent properties of free-living nematode assemblages exposed to multiple stresses

Biological communities are currently facing multi-stressor scenarios whose ecological impacts are challenging to estimate. In that respect, considering the complex nature of ecosystems and types and interaction among stressors is mandatory. Microcosm approaches using free-living nematode assemblages can effectively be used to assess complexity since they preserve the interactions inherent to complex systems when testing for multiple stress effects. In this study, we investigated the interaction effects of three stress factors, namely i-metallic mixture of Cu, Pb, Zn, and Hg (control [L0], low, [L1] and high [L2]), ii- CO2-driven acidification (pH 7.6 and 8.0), and iii- temperature rise (26 and 28 °C), on estuarine free-living nematode assemblages. Metal contamination had the greatest influence on free-living nematode assemblages, irrespective of pH and temperature scenarios. Interestingly, whilst the most abundant free-living nematode genera showed significant decreases in their densities when exposed to contamination, other, less abundant, genera were apparently favored and showed significantly higher densities in contaminated treatments. The augmented densities of tolerant genera may be attributed to indirect effects resulting from the impacts of toxicity on other components of the system, indicating the potential for emergent effects in response to stress. Temperature and pH interacted significantly with contamination. Whilst temperature rise had potentialized contamination effects, acidification showed the opposite trend, acting as a buffer to the effects of contamination. Such results show that temperature rise and CO2-driven acidification interact with contamination on coastal waters, highlighting the importance of considering the intricate interplay of these co-occurring stressors when assessing the ecological impacts on coastal ecosystems.

Cortisol and epinephrine alter the adipose functions and the mobilization of PCBs in adipose tissue slices from elephant seal

Marine mammals are exposed to increasing intensities of anthropogenic stressors such as acoustic disturbance and contaminants. Correlative studies have suggested concerning shifts in behavioral and physiological status of stress-exposed individuals, which could alter the health and survival of marine mammal populations. However, functional studies of the effects of multiple stressors on marine mammals are lacking. To fill in this gap, we recently developed an ex vivo approach of precision-cut adipose tissue slices (PCATS) to study the impact of stressors on the function of an essential endocrine organ: the adipose tissue. In the present study, we investigated the impact of hormones associated with the stress response on adipose tissue from northern elephant seals (Mirounga angustirostris). Blubber biopsies were collected from 17 weaned northern elephant seal pups, separated into inner and outer layers, dissected into PCATS, and cultured for 48 hours. To mimic prolonged and short-term exposure to physiological stress, PCATS were treated with 2 µM cortisol (CORT) for the entire 48 hours or 100 nM epinephrine (EPI) for the last 12 hours of culture, respectively. Hormones were applied individually or in combination. CORT and EPI exhibited an interacting, blubber layer-dependent, effect on adipose tissue biology, as quantified by gene expression in PCATS, and release of glycerol, free fatty acids, leptin and polychlorinated biphenyls into culture media. EPI stimulated a higher rate of lipolysis than CORT in PCATS from both blubber layers. The combination of CORT and EPI upregulated the expression of adipose triglyceride lipase in inner blubber PCATS and downregulated hormone-sensitive lipase in outer blubber-derived PCATS. Expression of the leptin gene and secretion of the leptin adipokine were both decreased by EPI, while addition of CORT attenuated this effect in inner blubber PCATS only. CORT also increased the expression of the antioxidant enzyme glutathione peroxidase 3 in PCATS from both blubber layers. Polychlorinated biphenyls exhibited selective and limited mobilization from PCATS treated with stress hormones, highlighting the lipophilic properties of these toxic compounds. This study showed that physiological stress can impact several essential functions of marine mammal blubber, such as lipolysis and adipokine production.

Latent pesticide effects and their mechanisms

Short pulses of toxicants can cause latent effects that occur long after the contamination event and are currently unpredictable. Here, we introduce an analytical framework for mechanistically predicting latent effects considering interactive effects of multiple stressors and hormetic effect compensation. We conducted an extensive investigation using high temporal resolution microcosm data of the mayfly Cloeon dipterum exposed to the pyrethroid pesticide esfenvalerate for 1 h. For 6 pesticide concentrations and 3 food levels we identified daily general stress information and predicted their synergistic interactions using the Stress Addition Model (SAM). Our analysis revealed that, especially at low concentrations, latent effects contributed most to the overall effect. At low concentrations ranging from 1/100 to 1/10,000 of the acute LC50, resulting in a 30–15 % mortality, latent effects prevailed, accounting for 92 % to 100 % of the observed effects. Notably, the concentration causing 15 % mortality 29 days post-exposure was 1000 times lower than the concentration causing the same mortality 4 days post-exposure, emphasizing the time-dependent nature of this Latent-Effect-Amplification (LEA). We identified both acute mortality and latent effects of pesticides on emergence. Furthermore, we observed pesticide-induced compensation mechanisms at both individual and population levels, transforming the initial monotonic concentration-response relationship into a hormetic, tri-phasic response pattern. Combining these processes enabled a quantification of the underlying causes of latent effects. Our findings highlight that short-term pesticide exposures can lead to latent effects of particular significance, especially at low effect concentrations.

Can warming accelerate the decline of Odonata species in experimental paddies due to insecticide fipronil exposure?

Systemic insecticides are one of the causes of Odonata declines in paddy fields. Since rising temperatures associated with global warming can contribute to strengthen pesticide toxicity, insecticide exposures under increasing temperatures may accelerate the decline of Odonata species in the future. However, the combined effects of multiple stressors on Odonata diversity and abundance within ecosystems under various environmental conditions and species interactions are little known. Here, we evaluate the combined effects of the insecticide fipronil and warming on the abundance of Odonata nymphs in experimental paddies. We show that the stand-alone effect of the insecticide exposure caused a significant decrease in abundance of the Odonata community, while nymphs decreased synergistically in the combined treatments with temperature rise in paddy water. However, impacts of each stressor alone were different among species. This study provides experimental evidence that warming could accelerate a reduction in abundance of the Odonata community exposed to insecticides (synergistic effect), although the strength of that effect might vary with the community composition in targeted habitats, due mainly to different susceptibilities among species to each stressor. Community-based monitoring in actual fields is deemed necessary for a realistic evaluation of the combined effects of multiple stressors on biodiversity.

Interactive effects of multiple stressors with significant wave height exposure on farmed Atlantic salmon (Salmo salar) welfare along an inshore-offshore gradient

Fish farming is the fastest growing food production sector worldwide and now accounts for most human fish consumption. Expansion of finfish aquaculture to exposed offshore marine environments is appealing where additional sheltered areas are unavailable. While more energetic environments may reduce waste accumulation and parasite exposure, effects on fish health and wellbeing are largely speculative. The multiple stressors faced by fish on offshore farms may interact synergistically and increase their cumulative impact. We used 20 months of health and welfare data from eight Atlantic salmon (Salmo salar) sea pen farms in Scotland along a wave exposure gradient to assess the effects of, and interactions between, environmental variables and management treatments on fish mortality and parasite loads. While farms showed high variability in mortality rate and sea lice infections, multi-level Bayesian modelling indicated that wave exposure primarily modulated effects of other variables. Higher exposure farms showed steeper increases in mortality with time and with extreme temperatures. Similarly, sea lice infections tended to increase with time, with higher exposure farms seeing steeper increases at higher Amoebic Gill Disease (AGD) scores and at high temperatures. The effect of AGD was greater at slow water speeds. Treatments against parasites were more frequent at low exposure farms, leading to uncertainty in their impact on welfare across farms. The support for interactive effects of wave exposure with other variables rather than strong direct effects suggests an accumulation of chronic and acute stressors. Expansion of aquaculture to more energetic offshore environments may have negative impacts on fish health in some circumstances, requiring adaptation of practices. In particular, the stronger increase in mortality over time may have implications for cycle length in different environments, and the more dramatic impacts of the warmest temperatures at high exposure farms call for consideration of the change in water temperature both inshore and offshore.

Association of adversities and mental health among first- and second-generation Arab American young adults.

The prevalence of mental health problems among young adults is widely recognized. However, limited research has examined the mental health of Arab American young adults specifically. To address this gap in the literature, this study aimed to investigate the effects of multiple stressors including adverse childhood experiences (ACEs), discrimination, and bullying victimization on the mental health of first- and second-generation Arab American young adults. The participants (N = 162) were recruited from a Midwest university using online and in-person methods. They were screened and completed a demographic questionnaire and self-report measures of ACEs, discrimination, bullying victimization, and mental health. Hierarchical multiple regression analysis was conducted to examine the effect of psychosocial stressors on mental health and the moderating effect of generation (first vs. second) on that relationship. Female gender, increased perceived discrimination, and more ACEs were associated with lower mental health scores (β = -0.316, p < 0.001, β = -0.308, p < 0.001, and β = -0.230, p = 0.002, respectively). There was a significant negative relationship between victimization and mental health for first-generation Arab Americans (β = -0.356, p = 0.010). However, that association all but disappeared for second-generation participants (β = 0.006, p = 0.953). The results highlight the impact of multiple adversities on Arab American young adults'mental health and indicate important nuances related to their generation in the association between bullying victimization and mental health. Implications for practice and future research are discussed.

Winter is coming: Interactions of multiple stressors in winter and implications for the natural world.

Winter is a key driver of ecological processes in freshwater, marine and terrestrial ecosystems, particularly in higher latitudes. Species have evolved various adaptive strategies to cope with food limitations and the cold and dark wintertime. However, human-induced climate change and other anthropogenic stressors are impacting organisms in winter in unpredictable ways. In this paper, we show that global change experiments investigating multiple stressors have predominantly been conducted during summer months. However, effects of anthropogenic stressors sometimes differ between winter and other seasons, necessitating comprehensive investigations. Here, we outline a framework for understanding the different effects of anthropogenic stressors in winter compared to other seasons and discuss the primary mechanisms that will alter ecological responses of organisms (microbes, animals and plants). For instance, while the magnitude of some anthropogenic stressors can be greater in winter than in other seasons (e.g. some pollutants), others may alleviate natural winter stress (e.g. warmer temperatures). These changes can have immediate, delayed or carry-over effects on organisms during winter or later seasons. Interactions between stressors may also vary with season. We call for a renewed research direction focusing on multiple stressor effects on winter ecology and evolution to fully understand, and predict, how ecosystems will fare under changing winters. We also argue the importance of incorporating the interactions of anthropogenic stressors with winter into ecological risk assessments, management and conservation efforts.

Decoupling the heterogeneity of sediment microbial communities along the urbanization gradients: A Bayesian-based approach

Comprehending the response of microbial communities in rivers along urbanization gradients to hydrologic characteristics and pollution sources is critical for effective watershed management. However, the effects of complex factors on riverine microbial communities remain poorly understood. Thus, we established a bacteria-based index of biotic integrity (Ba-IBI) to evaluate the microbial community heterogeneity of rivers along an urbanization gradient. To examine the response of Ba-IBI to multiple stressors, we employed a Bayesian network based on structural equation modeling (SEM-BN) and revealed the key control factors influencing Ba-IBI at different levels of urbanization. Our findings highlight that waterborne nutrients have the most significant direct impact on Ba-IBI (r = −0.563), with a particular emphasis on ammonia nitrogen, which emerged as the primary driver of microbial community heterogeneity in the Liuyang River basin. In addition, our study confirmed the substantial adverse effects of urbanization on river ecology, as urban land use had the greatest indirect effect on Ba-IBI (r = −0.460). Specifically, the discharge load from wastewater treatment plants (WWTP) was found to significantly negatively affect the Ba-IBI of the entire watershed. In the low urbanized watersheds, rice cultivation (RC) and concentrated animal feeding operations (CAFO) are key control factors, and an increase in their emissions can lead to a sharp decrease in Ba-IBI. In moderately urbanized watersheds, the Ba-IBI tended to decrease as the level of RC emissions increased, while in those with moderate RC emissions, an increase in point source emissions mitigated the negative impact of RC on Ba-IBI. In highly urbanized watersheds, Ba-IBI was not sensitive to changes in stressors. Overall, our study presents a novel approach by integrating Ba-IBI with multi-scenario analysis tools to assess the effects of multiple stressors on microbial communities in river sediments, providing valuable insights for more refined environmental decision-making.

Soil biota associated with soil N cycling under multiple anthropogenic stressors in grasslands

Soil nitrogen (N) processes and statuses are two essential components for soil N cycling in terrestrial ecosystems. Although studies have estimated the effects of multiple anthropogenic stressors (e.g., nutrient enrichment and soil acidification) on soil N cycling, how multiple trophic levels of soil biota regulate the responses of soil N processes and statuses under multiple anthropogenic stressors has not yet been studied. We established an N and phosphorus (P) enrichment and acid addition experiment in a semi-arid grassland on the Mongolian Plateau. After five years, our results showed that soil acidification strongly inhibited soil N processes (via decreasing N mineralization rate, potential nitrification rate, and potential denitrification rate) and soil N statuses (via decreasing dissolved organic N, NO3−-N, and microbial biomass N). Acid addition-induced declines in soil N processes or N statuses were mainly associated with the inhibition of the abundance/richness of soil N-related bacteria and nematodes. Compared with soil acidification, N or P enrichment had relatively minor effects on soil N processes or N statuses, except for the N enrichment-induced decline in the potential nitrification rate and increase in soil NH4+-N and P enrichment-induced decline in soil NO3−-N. Furthermore, we found that the responses of soil N processes or statuses to nutrient enrichment were different between non-acidified soils and acidified soils. Overall, our results evidenced that soil biota strongly mediated the responses of soil N processes and statuses to nutrient enrichment and acid addition in semi-arid grasslands, and soil acidification weakened the associations between soil biota and soil N cycling. These findings indicate that we should concentrate more on the importance of soil biota in maintaining ecosystem N functions and services against a background of global change.

Multiple stressor effects of insecticide exposure and increased fine sediment deposition on the gene expression profiles of two freshwater invertebrate species

BackgroundFreshwater ecosystem degradation and biodiversity decline are strongly associated with intensive agricultural practices. Simultaneously occurring agricultural stressors can interact in complex ways, preventing an accurate prediction of their combined effects on aquatic biota. Here, we address the limited mechanistic understanding of multiple stressor effects of two globally important stressors, an insecticide (chlorantraniliprole), and increased fine sediment load and assessed their impact on the transcriptomic profile of two stream macroinvertebrates: the amphipod Gammarus pulex and the caddisfly Lepidostoma basale.ResultsWe identified mainly antagonistic stressor interactions at the transcriptional level, presumably because the insecticide adsorbed to fine sediment particles. L. basale, which is phylogenetically more closely related to the insecticide’s target taxon Lepidoptera, exhibited strong transcriptional changes when the insecticide stressor was applied, whereas no clear response patterns were observed in the amphipod G. pulex. These differences in species vulnerability can presumably be attributed to molecular mechanisms determining the cellular affinity toward a stressor as well as differential exposure patterns resulting from varying ecological requirements between L. basale and G. pulex. Interestingly, the transcriptional response induced by insecticide exposure in L. basale was not associated with a disruption of the calcium homeostasis, which is the described mode of action for chlorantraniliprole. Instead, immune responses and alterations of the developmental program appear to play a more significant role.ConclusionsOur study shows how transcriptomic data can be used to identify multiple stressor effects and to explore the molecular mechanisms underlying stressor-induced physiological responses. As such, stressor effects assessed at the molecular level can inform about modes of action of chemicals and their interplay with non-chemical stressors. We demonstrated that stressor effects vary between different organismic groups and that insecticide effects are not necessarily covered by their described mode of action, which has important implications for environmental risk assessment of insecticides in non-target organisms.