The salinization of the global freshwater system caused by various human activities and climate change has become a common problem threatening freshwater biodiversity and resources, which may affect a variety of species of cladocerans at individual and population levels. In order to comprehensively evaluate the impact of salinization on different-sized cladocerans at individual and population levels, we exposed two species of cladocerans with obvious body size difference, Daphnia magna and Moina macrocopa, to seven salinities (0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12 M), recorded individual life history traits and population growth dynamics, and used multiple mechanistic models to fit the data. At the individual level, the median effect concentration of survival time, total offspring per female, and number of broods of D. magna were significantly higher than those of M. macrocopa. At the population level, the decrease in carrying capacity of D. magna with increasing salinity was significantly less than that of M. macrocopa. At the same salinity treatment, the integrated biomarker response indexes value of M. macrocopa is higher than that of D. magna. Therefore, it was further inferred that the sensitivity of small-sized species M. macrocopa to salinity stress is significantly higher than that of big-sized species D. magna. Thus, freshwater salinization may result in the replacement of smaller salt-intolerant cladocerans with larger salt-tolerant cladocerans, which may have dramatic effects on freshwater communities and ecosystems. Additionally, the increase of salinity had a greater impact on the population level of D. magna and M. macrocopa than on the individual level, indicating that population level of cladocerans was more susceptible to salinity stress. Experiments only based on individuals may underestimate the ecologically related changes in populations and communities, thus understanding the impact of salinization on freshwater systems needs to consider multiple ecological levels.

The removal efficiency of antibiotic resistance genes (ARGs) is the biggest challenge for the treatment of erythromycin fermentation residue (EFR). In the current research, 0% (control), 10% (T1), and 30% (T2) spray-dried EFR were composted with bulking materials, consisting of cattle manure and maize straw, for 30 days. Environmental factors and bacterial community on the behaviors of ARGs were further investigated. Apart from the high levels of erythromycin, the electrical conductivities were also increased by 66.7% and 291.7% in the samples of T1 and T2, respectively. After 30 days of composting, total ARGs in the samples of control were decreased by 78.1%–91.2%, but those of T1 and T2 were increased 14.5–16.7- and 38.5–68.7-fold. ARGs related to ribosomal protection (erm) dominated the samples of T1 and T2 at D 13 and 30, especially that ermF accounted for more than 80% of the total ARGs. Furthermore, the results of bacterial community revealed that EFR promoted the growth of Proteobacteria and Bacteroidetes, but inhibited that of Actinobacteria, Verrucomicrobia and Chloroflexi. Network analysis revealed that the enriched ARGs had strong correlation with seven bacterial genera, including Halomonas, Oceanobacillus, and Alcaligenes, most of which are halotolerant. Above all, erythromycin combined with high salinity can have synergistic effect on the enrichment of ARGs and their hosts.

Soil salinity is a global threat to the environmental sustainability, in particular to the developing countries due to their limited resources for soil reclamation. In a greenhouse pot experiment, Pennisetum giganteum, was investigated for its tolerance to salt stress and simultaneous phytoremediation capability. 4 weeks post-germination, NaCl (10, 50, 150, 250, 350, 450 and 550 mM) and tap water (control) was applied after every 2 consecutive days for two weeks in a completely randomized design and their effects were established in the growth and physico-chemical aspects of these plants. Our results indicated that P. giganteum withstood high salt stress (with 550 mM NaCl tolerance threshold level). Interestingly, the plants grown under saline conditions had higher biomass yield when compared to the control. Furthermore, the antioxidant activity and proline content of plants under saline conditions were significantly (p < 0.05) higher than those of control plants, indicating their adaptability to high salt stress. Biochemical analysis such as chlorophyll contents, total soluble sugar, total phenol and protein contents revealed considerable differences between plants grown under higher NaCl stress compared to the control conditions. Additionally, significantly different ionic flux along with high K⁺/Na⁺ ratio was observed in plants grown under a range of saline conditions. The results obtained are therefore of value to indicate P. giganteum an eco-friendly alternate source for the phytoremediation of saline soils and may be used as base for future research on this plant. Effective strategies need to be adopted with this plant to reclaim saline-degraded as well as marginal soils.

In spite of being a widespread activity causing the salinization of rivers worldwide, the impact of potash mining on river ecosystems is poorly understood. Here we used a mesocosm approach to test the effects of a salt effluent coming from a potash mine on algal and aquatic invertebrate communities at different concentrations and release modes (i.e. press versus pulse releases). Algal biomass was higher in salt treatments than in control (i.e. river water), with an increase in salt-tolerant diatom species. Salt addition had an effect on invertebrate community composition that was mainly related with changes in the abundance of certain taxa. Short (i.e. 48 h long) salt pulses had no significant effect on the algal and invertebrate communities. The biotic indices showed a weak response to treatment, with only the treatment with the highest salt concentration causing a consistent (i.e. according to all indices) reduction in the ecological quality of the streams and only by the end of the study. Overall, the treatment's effects were time-dependent, being more clear by the end of the study. Our results suggest that potash mining has the potential to significantly alter biological communities of surrounding rivers and streams, and that specific biotic indices to detect salt pollution should be developed.

The deposition of chemical pollutants into roadside wetlands from runoff is a current environmental concern. In northern latitudes, a major pollutant in runoff water is salt (NaCl), used as de-icing agents. In this study, 26 roadside ponds were surveyed for amphibian species richness and chloride concentration. Acute toxicity tests (LC50) were performed on five locally common amphibian species using a range of environmentally significant NaCl concentrations. Field surveys indicated that spotted salamanders (Ambystoma maculatum) and wood frogs (Rana sylvatica) did not occupy high chloride ponds. American toads (Bufo americanus) showed no pond preference based on chloride concentration. Acute toxicity tests showed spotted salamanders and wood frogs were most sensitive to chloride, and American toads were the least. Spring peepers (Pseudacris crucifer) and green frogs (Rana clamitans) showed intermediate sensitivities. We concluded that chloride concentrations in ponds due to application of de-icing salts, influenced community structure by excluding salt intolerant species. Salt toxicity is presented as a mechanism affecting the distribution of amphibians and structure of amphibian communities in roadside wetlands.

Salinity stress seriously threatens agricultural productivity and food security worldwide. This work reports on the mechanisms of alleviating salinity stress by cerium oxide nanomaterials (CeO2 NMs) in maize (Zea may L.). Soil-grown maize plants were irrigated with deionized water or 100 mM NaCl solution as the control or the salinity stress treatment. CeO2 NMs (1, 5, 10, 20, and 50 mg/L) with antioxidative enzyme mimicking activities were foliarly applied on maize leaves for 7 days. The morphological, physiological, biochemical, and transcriptomic responses of maize were evaluated. Specifically, salinity stress significantly reduced 59.0% and 63.8% in maize fresh and dry biomass, respectively. CeO₂ NMs at 10, 20, and 50 mg/L improved the salt tolerance of maize by 69.5%, 69.1%, and 86.8%, respectively. Also, 10 mg/L CeO₂ NMs maintained Na⁺/K⁺ homeostasis, enhanced photosynthetic efficiency by 30.8%, and decreased reactive oxygen species (ROS) level by 58.5% in salt-stressed maize leaves. Transcriptomic analysis revealed that the antioxidative defense system-related genes recovered to the normal control level after CeO₂ NMs application, indicating that CeO₂ NMs eliminated ROS through their intrinsic antioxidative enzyme properties. The down-regulation of genes related to lignin synthesis in the phenylpropanoid biosynthesis pathway accelerated leaf cell elongation. In addition, CeO₂ NMs increased the rhizobacteria richness and diversity through the increment of carbon source in root exudates and improved the abundance of halotolerant plant growth-promoting rhizobacteria (HT-PGPR). Importantly, the yield of salt-stressed maize was enhanced by 293.3% after 10 mg/L CeO₂ NMs foliar application. These results will provide new insights for the application of CeO₂ NMs in management to reduce the salinity-caused crop loss.

Serious environmental pollution of heavy metals has attracted people's attention in recent years and halophiles seem to be potential bioremediation in the controlling of heavy metals contamination. In this study, the adaptive mechanism of halophilic Brachybacterium muris (B. muris) in response to salt stress and its mitigation of copper (Cu) toxicity in hydroponic plants were investigated. The cell morphology was observed using transmission electron microscopy. The cell membrane composition and fluidity were examined by the combination of gas chromatography, gas chromatography-mass spectrometry, ultra-high performance liquid chromatography-mass spectrometry, and fluorescence spectrophotometry. Moreover, the metabolic pathways of B. muris in response to salt stress were analyzed using the prokaryotic transcriptomics approach. A hydroponic co-culture model was further conducted to explore the effects of B. muris on wheat seedlings subjected to Cu toxicity. It was found that B. muris can respond to high osmotic pressure by improving the cell membrane fluidity, altering the cell morphology and cell membrane compositions. The proportion of unsaturated fatty acids, phosphatidylethanolamine, and phosphatidylinositol in B. muris cell membranes increased significantly, while zymosterol, fecosterol, and ergosterol contents decreased under a high salinity situation. Further transcriptomic analysis showed that genes encoding L-glutamate synthase, glutamate ABC transporter ATP-binding protein, and sodium cotransporter were up-regulated, indicating that both the synthesis and transport of glutamate were significantly enhanced under high osmotic pressure. Additionally, B. muris alleviated the inhibitory effect of Cu²⁺ on wheat seedlings' growth, causing a 30.14% decrease in H₂O₂ content and a significant increase of 83.86% and 45.96% in POD activity and GSH content in wheat roots, respectively. The findings of this study suggested that the salt-tolerant B. muris may serve as a promising strategy for improving the bioremediation of metal-contaminated saline water and soils.

Constructed wetlands (CWs) inoculated with exogenous microbes have great potential for removing pollutants in adverse environments. The rapid loss of functional bacteria and the high cost of repeated additions of inoculum, however, limit the practical application of this technology. In this study, C–F2 immobilized bacteria (i.e., immobilized salt-tolerant bacterium Alishewanella sp. F2 incorporated with a carbon source) were developed and utilized in CWs for solving the above problems. A 60-day experiment demonstrated that bioaugmented CWs (Bio-CWs) with the addition of C–F2 immobilized bacteria into the bottom gravel layer of CW microcosms (B-CF2 treatment) exhibited high nitrogen removal efficiency under a saline condition (electrical conductivity of 15 mS/cm). We measured mean nitrate nitrogen (NO₃⁻-N) and total nitrogen (TN) removal percentages of 97.8% and 88.1%, respectively, which were significantly (p < 0.05) higher than those in Bio-CWs with microbial inoculum (MI-F2 treatment, 63.5% and 78.2%) and unbioaugmented CWs (CK, 48.7% and 67.2%). The TN content of the entire plant was significantly (p < 0.05) increased in B-CF2 (636.06 mg/microcosm) compared with CK (372.06 mg/microcosm). The relative abundances of the genera Alishewanella (i.e., the exogenous bacterium, 5.5%), Clostridium-XlVa (8.8%) and Bacteroides (21.1%) in B-CF2 were significantly (p < 0.05) higher than in MI-F2 and CK, which improved the denitrification capacity of CWs. Overall, a high denitrification efficiency and durability were achieved in the newly developed Bio-CWs (i.e., B-CF2 treatment) with immobilized bacteria under saline conditions, which provides an alternative technology for the rapid removal of nitrogen from saline wastewater.

Secondary salinisation of rivers and streams is a global and growing threat that might be amplified by climate change. It can have many different causes, like irrigation, mining activity or the use of salts as de-icing agents for roads. Freshwater organisms only tolerate certain ranges of water salinity. Therefore secondary salinisation has an impact at the individual, population, community and ecosystem levels, which ultimately leads to a reduction in aquatic biodiversity and compromises the goods and services that rivers and streams provide. Management of secondary salinization should be directed towards integrated catchment strategies (e.g. benefiting from the dilution capacity of the rivers) and identifying threshold salt concentrations to preserve the ecosystem integrity. Future research on the interaction of salinity with other stressors and the impact of salinization on trophic interactions and ecosystem properties is needed and the implications of this issue for human society need to be seriously considered.

Organisms that rely on aquatic habitats in roaded landscapes face a growing array of consequences from pollution, especially due to freshwater salinization. Critically, these consequences can vary from population to population depending on exposure histories and evolutionary responses. Prior studies using transplant and common garden experiments have found that aquatic-stage wood frogs (Rana sylvatica) from roadside populations are less fit in the wild and more sensitive to road salt than their counterparts from woodland populations away from roads. While this pattern is consistent with local maladaptation, unresolved insights into the timing and duration of these effects leave open the possibility that negative outcomes are countered during development. Here, we asked whether the survival disadvantage of roadside wood frogs is stage-specific, and whether this disadvantage reverses before metamorphosis. We used a common garden road salt exposure experiment and a field-based reciprocal transplant experiment to examine differences in survival across life-history stage and with respect to population type. In each experimental context, roadside embryos showed a survival disadvantage relative to woodland embryos, and this disadvantage was not reversed prior to metamorphosis. We also found that salt exposure delayed metamorphosis more strongly for roadside than woodland populations. Together, these results suggest that local maladaptation in aquatic-stage wood frogs is driven by embryonic sensitivity to salt and that roadside populations are further compromised by delayed developmental rates. Future studies should consider which embryonic traits fail to adapt to salt toxicity, and how those traits might correlate with terrestrial trait variation.