Effective remediation of agricultural drainage at three influent strengths by bioaugmented constructed wetlands filled with mixture of iron­carbon and organic solid substrates: Performance and mechanisms.

Agricultural drainage containing a large quantity of nutrients can cause quality deterioration and algal blooming of receiving water bodies, thus needs to be effectively remediated. In this study, iron­carbon (FeC) composite-filled constructed wetlands (Fe-C-CWs) were employed to treat farmland drainage at three pollution levels, and organic solid substrates (walnut shells) and phosphate-accumulating denitrifying bacteria (Pseudomonas sp. DWP1) were supplemented to enhance the treatment performance. The results showed that the Fe-C-CWs exhibited notably superior removal efficiency for total nitrogen (TN, 52.0-58.2 %), total phosphorus (TP, 67.8-70.2 %) and chemical oxygen demand (COD, 56.7-70.4 %) than the control systems filled solely with gravel (28.5-32.5 % for TN, 33.2-40.5 % for TP and 30.2-55.0 % for COD) at all influent strengths, through driving autotrophic denitrification, Fe-based dephosphorization, and organic degradation processes. The addition of organic substrates and functional bacteria markedly enhanced pollutant removal in the Fe-C-CWs. Furthermore, use of FeC and organic substrates and denitrifier inoculation decreased CO2 and CH4 emissions from the CWs, and reduced global warming potential of the CWs at low influent strength. Pollutant removal efficiencies in the CWs were only marginally impacted by the increasing influent loads except for NO3--N, and pollutant removal mass was largely increased with the increase of influent strengths. The microbial community in the FeC composite-filled CWs exhibited distinct distribution patterns compared to the gravel-filled CWs regardless of the influent strengths, with obviously higher proportions of dominant genera Trichococcus, Geobacter and Ferritrophicum. Keystone taxa associated with pollutant removal in the Fe-C-filled CWs were identified to be Pseudomonas, Geobacter, Ferritrophicum, Denitratisoma and Sediminibacterium. The developed augmented Fe-C-filled CWs show great promises for remediating agricultural drainage with varied pollutant loads.

Integrated Transcriptomic and Metabolomic Analysis Reveals the Molecular Regulatory Mechanism of Flavonoid Biosynthesis in Maize Roots under Lead Stress.

Flavonoids are secondary metabolites that play important roles in the resistance of plants to abiotic stress. Despite the widely reported adverse effects of lead (Pb) contamination on maize, the effects of Pb on the biosynthetic processes of flavonoids in maize roots are still unknown. In the present work, we employed a combination of multi-omics and conventional assay methods to investigate the effects of two concentrations of Pb (40 and 250 mg/kg) on flavonoid biosynthesis in maize roots and the associated molecular regulatory mechanisms. Analysis using conventional assays revealed that 40 and 250 mg/kg Pb exposure increased the lead content of maize root to 0.67 ± 0.18 mg/kg and 3.09 ± 0.02 mg/kg, respectively, but they did not result in significant changes in maize root length. The multi-omics results suggested that exposure to 40 mg/kg of Pb caused differential expression of 33 genes and 34 metabolites related to flavonoids in the maize root system, while 250 mg/kg of Pb caused differential expression of 34 genes and 31 metabolites. Not only did these differentially expressed genes and metabolites participate in transferase activity, anthocyanin-containing compound biosynthetic processes, metal ion binding, hydroxyl group binding, cinnamoyl transferase activity, hydroxycinnamoyl transferase activity, and flavanone 4-reductase activity but they were also significantly enriched in the flavonoid, isoflavonoid, flavone, and flavonol biosynthesis pathways. These results show that Pb is involved in the regulation of maize root growth by interfering with the biosynthesis of flavonoids in the maize root system. The results of this study will enable the elucidation of the mechanisms of the effects of lead on maize root systems.

Trifolium repens L. recruits root-associated Microbacterium species to adapt to heavy metal stress in an abandoned Pb-Zn mining area.

Root-associated microbiota provide great fitness to hosts under environmental stress. However, the underlying microecological mechanisms controlling the interaction between heavy metal-stressed plants and the microbiota are poorly understood. In this study, we screened and isolated representative amplicon sequence variants (strain M4) from rhizosphere soil samples of Trifolium repens L. growing in areas with high concentrations of heavy metals. To investigate the microecological mechanisms by which T. repens adapts to heavy metal stress in abandoned mining areas, we conducted potting experiments, bacterial growth promotion experiments, biofilm formation experiments, and chemotaxis experiments. The results showed that high concentrations of heavy metals significantly altered the rhizosphere bacterial community structure of T. repens and significantly enriched Microbacterium sp. Strain M4 was demonstrated to significantly increased the biomass and root length of T. repens under heavy metal stress. Additionally, L-proline and stigmasterol could promote bacterial growth and biofilm formation and induce chemotaxis for strain M4, suggesting that they are key rhizosphere secretions of T. repens for Microbacterium sp. recruitment. Our results suggested that T. repens adapted the heavy metal stress by reshaping rhizosphere secretions to modify the rhizosphere microbiota.

Reshaping the root endophytic microbiota in plants to combat mercury-induced stress.

Emerging evidence suggests that plants experiencing abiotic stress actively seek help from soil microbes. However, the empirical evidence supporting this strategy is limited, especially in response to heavy metal stress. We used integrated microbial community profiling and culture-based methods to investigate the interaction between mercury (Hg) stress, the entophytic root microbiome, and maize seedlings. The results of the pot experiment showed that soil Hg (20 mg/kg) strongly inhibited maize growth, indicating its strong phytotoxicity. Furthermore, Hg stress significantly altered the structure of the bacterial and fungal communities and enriched the potentially pathogenic Fusarium sp., suggesting that soil Hg stress may enhance the bio-stress induced by Fusarium species in maize. Additionally, soil Hg also led to the enrichment of beneficial bacterial members of Streptomyces, Lysobacter, and Sphingomonas (defined as differential species), which were also identified as keystone species in the Hg treatment by the analysis of co-occurrence networks. Therefore, it can be postulated that the members of Streptomyces, Lysobacter, and Sphingomonas function as stress-alleviating microbes. We successfully isolated the representatives of these stress-alleviating microbes. As expected, these strains mitigated the detrimental effects of Hg stess for the maize seedlings, suggesting that plants recruit the stress-alleviated microbiota to combat Hg stress. This study provides insights into the potential of manipulating the root microbiome to enhance plant growth in polluted environments.

Phosphorus stoichiometric homeostasis of submerged macrophytes and associations with interspecific interactions and community stability in Erhai Lake, China.

According to stoichiometric homeostasis theory, eutrophication is expected to increase the dominance of submerged macrophytes with low homeostatic regulation coefficients (H) relative to those with high H values, ultimately reducing macrophyte community stability. However, empirical evidence supporting this hypothesis is limited. In this study, we conducted a three-year tracking survey (seven sampling events) at 81 locations across three regions of Erhai Lake. We assessed the H values of submerged macrophyte species, revealing significant H values for phosphorus (P) and strong associations of HP values (range: 1.58-2.94) with species and community stability. Moreover, in plots simultaneously containing the dominant high-HP species, Potamogeton maackianus, and its low-HP counterpart, Ceratophyllum demersum, we explored the relationships among eutrophication, interspecific interaction shifts, and community dynamics. As the environmental P concentration increased, the dominance of P. maackianus decreased, while that of C. demersum increased. This shift coincided with reductions in community HP and stability. Our study underpins the effectiveness of H values for forecasting interspecific interactions among submerged macrophytes, thereby clarifying how eutrophication contributes to the decline in stability of the submerged macrophyte community.

Soil microbial communities' contributions to soil ecosystem multifunctionality in the natural restoration of abandoned metal mines.

On a global scale, the restoration of metal mine ecosystem functions is urgently required, and soil microorganisms play an important role in this process. Conventional studies frequently focused on the relationship between individual functions and their drivers; however, ecosystem functions are multidimensional, and considering any given function in isolation ignores the trade-offs and interconnectedness between functions, which complicates obtaining a comprehensive understanding of ecosystem functions. To elucidate the relationships between soil microorganisms and the ecosystem multifunctionality (EMF) of metal mines, this study investigated natural restoration of metal mines, evaluated the EMF, and used high-throughput sequencing to explore the bacterial and fungal communities as well as their influence on EMF. Bacterial community diversity and composition were more sensitive to mine restoration than fungal community. Bacterial diversity exhibited redundancy in improving N-P-K-S multifunctionality; however, rare bacterial taxa including Dependentiae, Spirochaetes, and WPS-2 were important for metal multifunctionality. Although no clear relationship between fungal diversity and EMF was observed, the abundance of Glomeromycota had a significant effect on the three EMF categories (N-P-K-S, carbon, and metal multifunctionality). Previous studies confirmed a pronounced positive association between microbial diversity and multifunctionality; however, the relationship between microbial diversity and multifunctionality differs among functions' categories. In contrast, the presence of critical microbial taxa exerted stronger effects on mine multifunctionality.

Changes in soil microbe-mediated carbon, nitrogen and phosphorus cycling during spontaneous succession in abandoned PbZn mining areas.

The mechanism through which soil microorganisms mediate carbon and nutrient cycling during mine wasteland restoration remained unknown. Using soil metagenome sequencing, we investigated the dynamic changes in soil microbial potential metabolic functions during the transition from biological soil crusts (BSC) to mixed broad-conifer forest (MBF) in a typical PbZn mine. The results showed soil microorganisms favored carbon sequestration through anaerobic and microaerobic pathways, predominantly using efficient, low-energy pathways during succession. Genes governing carbon degradation and aerobic respiration increased by 19.56 % and 24.79 %, respectively, reflecting change toward more efficient and intensive soil carbon utilization in late succession. Nitrogen-cycling genes mediated by soil microorganisms met their maximum influence during early succession (sparse grassland, SGL), leading to a respective increase of 75.29 % and 76.81 % in the net potential nitrification rate and total nitrogen content. Mantel and correlation analyses indicated that TOC, TN, Zn and Cd contents were the main factors affecting the soil carbon and phosphorus cycles. Soil AP content emerged as the primary influencer of genes associated with the nitrogen cycle. These results shed light on the dynamic shifts in microbial metabolic activities during succession, providing a genetic insight into biogeochemical cycling mechanisms and underscoring crucial factors influencing soil biogeochemical processes in mining regions.

Opposite response of constructed wetland performance in nitrogen and phosphorus removal to short and long terms of operation.

Constructed wetlands (CWs) have been widely used for treating polluted water since the 1950s, with applications in over 50 countries worldwide. Most studies investigating the pollutant removal efficiency of these wetlands have focused on differences among wetland designs, operation strategies, and environmental conditions. However, there still remains a gap in understanding the variation in wetland pollutant removal efficiency over different time scales. Therefore, the main aim of the study is to address this gap by conducting a global meta-analysis to estimate the variation in nitrogen (N) and phosphorus (P) removal by wetland in short- and long-term pollutant treatment. The findings of this study indicated that the total efficiencies of N and P removal increased during short-term wetland operation but decreased during long-term operation. However, for surface flow CWs specifically, the efficiencies of N and P removal increased during short-term operation and remained stable during long-term operation. Moreover, the study discovered that wetland N removal efficiency was influenced by seasons, with an increase in spring and summer and a decrease in autumn and winter. Conversely, there was no significant seasonal effect on P removal efficiency. Additionally, high hydraulic load impaired wetland N and P removal efficiency during long-term operation. This study offers a critical review of the role of wetlands in wastewater treatment and provides valuable reference data for the design and selection of CWs types during wastewater treatment in the aspect of sustainability.

Mechanisms involved in the sequestration and resistance of cadmium for a plant-associated Pseudomonas strain.

Understanding Cd-resistant bacterial cadmium (Cd) resistance systems is crucial for improving microremediation in Cd-contaminated environments. However, these mechanisms are not fully understood in plant-associated bacteria. In the present study, we investigated the mechanisms underlying Cd sequestration and resistance in the strain AN-B15. These results showed that extracellular Cd sequestration by complexation in strain AN-B15 was primarily responsible for the removal of Cd from the solution. Transcriptome analyses have shown that the mechanisms of Cd resistance at the transcriptional level involve collaborative processes involving multiple metabolic pathways. The AN-B15 strain upregulated the expression of genes related to exopolymeric substance synthesis, metal transport, Fe-S cluster biogenesis, iron recruitment, reactive oxygen species oxidative stress defense, and DNA and protein repair to resist Cd-induced stress. Furthermore, inoculation with AN-B15 alleviated Cd-induced toxicity and reduced Cd uptake in the shoots of wheat seedlings, indicating its potential for remediation. Overall, the results improve our understanding of the mechanisms involved in Cd resistance in bacteria and thus have important implications for improving microremediation.

Drivers and mechanisms of spontaneous plant community succession in abandoned PbZn mining areas in Yunnan, China.

The drivers and mechanisms underlying succession and the spontaneous formation of plant communities in mining wasteland remain largely unknown. This study investigated the use of nature-based restoration to facilitate the recovery of viable plant communities in mining wasteland. It was found that scientific analyses of spontaneously formed plant communities in abandoned mining areas can provide insights for nature-based restoration. A chronosequence ("space for time") approach was used to establish sites representing three successional periods with six successional stages, and 90 quadrats were constructed to investigate changes in plant species and functional diversity during succession in abandoned PbZn mining areas. A total of 140 soil samples were collected to identify changes in soil properties, including plant nutrient and heavy metal concentrations. Then, this paper used structural equation models to analyze the mechanisms that drive succession. It was found that the functional diversity of plant communities fluctuated substantially during succession. Species had similar functional traits in early and mid-succession, but traits tended to diverge during late succession. Soil bulk density and soil organic matter gradually increased during succession. Total nitrogen (N), pH, and soil Zn concentrations first increased and then decreased during succession. Concentrations of Mn and Cd gradually decreased during succession. During early succession, soil organic matter was the key factor driving plant colonization and succession. During mid-succession, soil Zn functioned as an environmental filter factor limiting the rates of succession in mining wasteland communities. During late succession, soil bulk density and competition for nutrient resources contributed to more balanced differentiation among plant species. This thesis proposed that a nature-based strategy for the stabilization of abandoned mining lands could facilitate effective plant community restoration that promotes ecosystem services and functioning.

The microbial mechanisms by which long-term heavy metal contamination affects soil organic carbon levels.

Globally, reducing carbon emissions and mitigating soil heavy metal pollution pose pressing challenges. We evaluated the effects of lead (Pb) and cadmium (Cd) contamination in the field over 20 years. The five treatment groups featured Pb concentrations of 40 and 250 mg/kg, Cd concentrations of 10 and 60 mg/kg, and a combination of Pb and Cd (60 and 20 mg/kg, respectively); we also included a pollution-free control group. After 20 years, soil pH decreased notably in all treatments, particularly by 1.02 in Cd10-treated soil. In addition to the increase of SOC in Cd10 and unchanged in Pb40 treatment, the SOC was reduced by 9.62%-12.98% under the other treatments. The α diversities of bacteria and fungi were significantly changed by Cd10 pollution (both p < 0.05) and the microbial community structure changed significantly. However, there were no significant changes in bacterial and fungal communities under other treatments. Cd10 pollution reduced the numbers of Ascomycota and Basidiomycota fungi, and enhanced SOC accumulation. Compared to the control, long-term heavy Cd, Pb, and Pb-Cd composite pollution caused SOC loss by increasing Basidiomycota which promoting carbon degradation, and decreasing Proteobacteria which promoting carbon fixation via the Krebs cycle. Our findings demonstrate that heavy metal pollution mediates Carbon-cycling microorganisms and genes, impacting SOC storage.

Effects of Heavy Metals on Stomata in Plants: A Review.

Stomata are one of the important structures for plants to alleviate metal stress and improve plant resistance. Therefore, a study on the effects and mechanisms of heavy metal toxicity to stomata is indispensable in clarifying the adaptation mechanism of plants to heavy metals. With the rapid pace of industrialization and urbanization, heavy metal pollution has been an environmental issue of global concern. Stomata, a special physiological structure of plants, play an important role in maintaining plant physiological and ecological functions. Recent studies have shown that heavy metals can affect the structure and function of stomata, leading to changes in plant physiology and ecology. However, although the scientific community has accumulated some data on the effects of heavy metals on plant stomata, the systematic understanding of the effects of heavy metals on plant stomata remains limited. Therefore, in this review, we present the sources and migration pathways of heavy metals in plant stomata, analyze systematically the physiological and ecological responses of stomata on heavy metal exposure, and summarize the current mechanisms of heavy metal toxicity on stomata. Finally, the future research perspectives of the effects of heavy metals on plant stomata are identified. This paper can serve as a reference for the ecological assessment of heavy metals and the protection of plant resources.

Green waste and sewage sludge feeding ratio alters co-composting performance: Emphasis on the role of bacterial community during humification.

Composting with five levels of green waste and sewage sludge was compared to examine how feeding ratios affected composting performance with special focus on humification, and the underlying mechanisms. The results showed that the raw material ratio persistently affected compost nutrients and stability. Humification and mineralization were promoted by higher proportion of sewage sludge. Bacterial community composition and within-community relationships were also significantly affected by the raw material feeding ratio. Network analysis indicated that clusters 1 and 4 which dominated by Bacteroidetes, Proteobacteria, and Acidobacteria shown significantly positive correlation with humic acid concentration. Notably, the structural equational model and variance partitioning analysis demonstrated that bacterial community structure (explained 47.82% of the variation) mediated the effect of raw material feeding ratio on humification, and exceeded the effect of environmental factors (explained 19.30% of the variation) on humic acid formation. Accordingly, optimizing the composting raw material improves the composting performance.

Plant Traits Guide Species Selection in Vegetation Restoration for Soil and Water Conservation.

Great efforts have been made to improve the soil and water conservation capacity by restoring plant communities in different climatic and land-use types. However, how to select suitable species from local species pools that not only adapt to different site environments, but also achieve certain soil and water conservation capacities is a great challenge in vegetation restoration for practitioners and scientists. So far, little attention has been paid to plant functional response and effect traits related to environment resource and ecosystem functions. In this study, together with soil properties and ecohydrological functions, we measured the seven plant functional traits for the most common species in different restoration communities in a subtropical mountain ecosystem. Multivariate optimization analyses were performed to identify the functional effect types and functional response types based on specific plant traits. We found that the community-weighted means of traits differed significantly among the four community types, and the plant functional traits were strongly linked with soil physicochemical properties and ecohydrological functions. Based on three optimal effect traits (specific leaf area, leaf size, and specific root length) and two response traits (specific leaf area and leaf nitrogen concentration), seven functional effect types in relation to the soil and water conservation capacity (interception of canopy and stemflow, maximum water-holding capacity of litter, maximum water-holding capacity of soil, soil surface runoff, and soil erosion) and two plant functional response types to soil physicochemical properties were identified. The redundancy analysis showed that the sum of all canonical eigenvalues only accounted for 21.6% of the variation in functional response types, which suggests that community effects on soil and water conservation cannot explain the overall structure of community responses related to soil resources. The eight overlapping species between the plant functional response types and functional effect types were ultimately selected as the key species for vegetation restoration. Based on the above results, we offer an ecological basis for choosing the appropriate species based on functional traits, which may be very helpful for practitioners involved in ecological restoration and management.

Resistance mechanisms and remediation potential of hexavalent chromium in Pseudomonas sp. strain AN-B15.

The understanding of bacterial resistance to hexavalent chromium [Cr(VI)] are crucial for the enhancement of Cr(VI)-polluted soil bioremediation. However, the mechanisms related to plant-associated bacteria remain largely unclear. In this study, we investigate the resistance mechanisms and remediation potential of Cr(VI) in a plant-associated strain, AN-B15. The results manifested that AN-B15 efficiently reduced Cr(VI) to soluble organo-Cr(III). Specifically, 84.3 % and 56.5 % of Cr(VI) was removed after 48 h in strain-inoculated solutions supplemented with 10 and 20 mg/L Cr(VI) concentrations, respectively. Transcriptome analyses revealed that multiple metabolic systems are responsible for Cr(VI) resistance at the transcriptional level. In response to Cr(VI) exposure, strain AN-B15 up-regulated the genes involved in central metabolism, providing the reducing power by which enzymes (ChrR and azoR) transformed Cr(VI) to Cr(III) in the cytoplasm. Genes involved in the alleviation of oxidative stress and DNA repair were significantly up-regulated to neutralize Cr(VI)-induced toxicity. Additionally, genes involved in organosulfur metabolism and certain ion transporters were up-regulated to counteract the starvation of sulfur, molybdate, iron, and manganese induced by Cr(VI) stress. Furthermore, a hydroponic culture experiment showed that toxicity and uptake of Cr(VI) by plants under Cr(VI) stress were reduced by strain AN-B15. Specifically, strain AN-B15 inoculation increased the fresh weights of the wheat root and shoot by 55.5 % and 18.8 %, respectively, under Cr(VI) stress (5 mg/L). The elucidation of bacterial resistance to Cr(VI) has an important implication for exploiting microorganism for the effective remediation of Cr(VI)-polluted soils.

Relationship between environmental pollution and economic development in late-developing regions shows an inverted V.

In late-developing regions, new technologies and previous experiences are applied to reduce the impact of economic development on environmental pollution in the early stages. After economic development has reached a certain level, the application of new environmental remediation technologies and methods can accelerate environmental restoration. Therefore, we hypothesized that the relationship between economic development and environmental pollution would exhibit an inverted V in late-developing regions. We examined water quality changes in 353 monitoring sections of 76 urban rivers in Kunming, southwestern China, over the last 33 years to assess the impact of economic development on river water quality. The results indicate that the relationship between the comprehensive pollution index of urban rivers and the economy shows an inverted V, supporting our hypothesis. The inverted V could be divided into four areas: an environmental self-purification area (<2170 USD); an economic development environmental destruction area (2170-5240 USD); an economic development feedback environment area (5240-11,255 USD); and an economic development promotion environment area (>11,255 USD). On the time axis of economic development, the relationship between economic development and environmental pollution is closer to an inverted U in relatively early developing regions, but the experience with and application of new technologies causes the relationship to change from an inverted U to an inverted V in relatively late-developing regions.

Community assembly during vegetation succession after metal mining is driven by multiple processes with temporal variation.

The mechanisms governing community assembly is fundamental to ecological restoration and clarification of the assembly processes associated with severe disturbances (characterized by no biological legacy and serious environmental problems) is essential. However, a systematic understanding of community assembly in the context of severe anthropogenic disturbance remains lacking. Here, we explored community assembly processes after metal mining, which is considered to be a highly destructive activity to provide insight into the assembly rules associated with severe anthropogenic disturbance. Using a chronosequence approach, we selected vegetation patches representing different successional stages and collected data on eight plant functional traits from each stage. The traits were classified as establishment and regenerative traits. Based on these traits, null models were constructed to identify the processes driving assembly at various successional stages. Comparison of our observations with the null models indicated that establishment and regenerative traits converged in the primary stage of succession. As succession progressed, establishment traits shifted to neutral assembly, whereas regeneration traits alternately converged and diverged. The observed establishment traits were equal to expected values, whereas regenerative traits diverged significantly after more than 20 years of succession. Furthermore, the available Cr content was linked strongly to species' ecological strategies. In the initial stages of vegetation succession in an abandoned metal mine, the plant community was mainly affected by the available metal content and dispersal limitation. It was probably further affected by strong interspecific interaction after the environmental conditions had improved, and stochastic processes became dominant during the stage with a successional age of more than 20 years.

Genome-Wide Analysis of the ATP-Binding Cassette (ABC) Transporter Family in Zea mays L. and Its Response to Heavy Metal Stresses.

The ATP-binding cassette (ABC) transporter family is one of the largest eukaryotic protein families. Its members play roles in numerous metabolic processes in plants by releasing energy for substrate transport across membranes through hydrolysis of ATP. Maize belongs to the monocotyledonous plant family, Gramineae, and is one of the most important food crops in the world. We constructed a phylogenetic tree with individual ABC genes from maize, rice, sorghum, Arabidopsis, and poplar. This revealed eight families, each containing ABC genes from both monocotyledonous and dicotyledonous plants, indicating that the amplification events of ABC gene families predate the divergence of plant monocotyledons. To further understand the functions of ABC genes in maize growth and development, we analyzed the expression patterns of maize ABC family genes in eight tissues and organs based on the transcriptome database on the Genevestigator website. We identified 133 ABC genes expressed in most of the eight tissues and organs examined, especially during root and leaf development. Furthermore, transcriptome analysis of ZmABC genes showed that exposure to metallic lead induced differential expression of many maize ABC genes, mainly including ZmABC 012, 013, 015, 031, 040, 043, 065, 078, 080, 085, 088, 102, 107, 111, 130 and 131 genes, etc. These results indicated that ZmABC genes play an important role in the response to heavy metal stress. The comprehensive analysis of this study provides a foundation for further studies into the roles of ABC genes in maize.

Efficient treatment of mercury(â ¡)-containing wastewater in aerated constructed wetland microcosms packed with biochar.

Effective removal of mercury (Hg) pollutants from contaminated water/wastewater to prevent severe environmental pollution is of great significance due to the extremely high toxicity of Hg. In this study, granular biochar and gravel (control) were packed into intermittently aerated constructed wetland (CW) microcosms to treat Hg(Ⅱ)-containing wastewater over 100 d. The results showed that the biochar-filled CWs exhibited notably better Hg(Ⅱ) removal than the gravel systems by facilitating chemical and microbial Hg(Ⅱ) reduction and volatilization and promoting plant growth and Hg assimilation. More than ten times more Hg was absorbed by the plants (L. salicaria) in biochar CWs than in the gravel systems, with the roots acting as the major sink. In contrast, substrate binding in a predominantly oxidizable fraction was the dominant pathway for Hg removal in the gravel CWs. Biochar substrates also exhibited higher levels of COD, N and P removal, and Hg(Ⅱ) import impacted the removal of these pollutants only slightly. Filling material played a more crucial role than Hg input in shaping the microbial communities in the CWs. The proportions of some dominant genera, including Arenimonas, Lysobacter, Micropruina and Hydrogenophaga, increased in the presence of Hg, implying their tolerance to Hg toxicity and potential roles in Hg detoxification in the CWs. Granular biochar-based CW has high potential for treating Hg(Ⅱ)-contaminated wastewater.

The effect of different restoration approaches on vegetation development in metal mines.

Mining is the most destructive human activity towards ecosystems through changing the terrain, substrate properties, and vegetation community structure. Vegetation succession, the theoretical basis of restoration, is influenced by site conditions and anthropogenic intervention. In order to provide general practical applications for mine restoration, it is critical to identify the optimal intervention that promotes succession, and the influence of climates. Here, we hypothesized that high-intervention contributes to positive characteristics and more successful succession, while increasing climatic severity presents negative characteristics and succession is hard to succeed. In this study, we collected 55 global studies (n = 804) on the vegetation succession of abandoned metal mines, and evaluated the ecological characteristics and successional trends under spontaneous succession and anthropogenic intervention conditions by conducting meta-analyses. Furthermore, we considered factors that may affect the vegetation succession after closing mines, including geological conditions, mining area (area of degraded land in mine field) and mining time (duration of mining operations). Species richness and evenness increased with the age of succession under low- and non- intervention conditions, while coverage increased under high-intervention, and species diversity decreased significantly with increasing mining time in cold areas. There were significant differences in succession trends under different climate types. The vegetation structure was more likely to develop towards the target vegetation in megathermal and mesothermal than in microthermal regions. We contend that a low level of intervention can help succession, while high-intervention will not. Vegetation succession can be achieved more easily with less climatic severity, and the reduction of large-scale mining processes (area and time) can increase vegetation evenness, especially for continental or microthermal regions.