Zinc toxicity thresholds for reclamation plants are largely unknown. As a result, ecological risk assessments often rely on toxicity thresholds for agronomic species, which may differ from those of restoration species. Our objective was to provide Zn toxicity thresholds for forb species that are commonly used in reclamation activities. We used a greenhouse screening study where seedlings of yarrow (Achillea millefolium L.), Bigelow's tansyaster (Machaeranthera bigelovii (Gray) Greene var. bigelovii), blue flax (Linum perenne L. var. Appar), alfalfa (Medicago sativa L. var. Ladak), Palmer's penstemon (Penstemon palmeri Gray), and Rocky Mountain penstemon (Penstemon strictus Benth. var. Bandera) were grown in sand culture and exposed to increasing concentrations of Zn. Lethal concentrations (LC50 - substrate Zn concentration resulting in 50% mortality), effective concentrations (EC50 - substrate Zn concentration resulting in 50% biomass reduction), and phytotoxicity thresholds (PT50 - tissue Zn concentration resulting in 50% biomass reduction) were then determined. Phytotoxicity thresholds and effective concentrations for these reclamation species were relatively consistent between species. Our estimates of PT50-shoot for these species range from 1258 to 3214 mg Zn kg-¹ . Measures of EC50-plant for these restoration forbs ranged from 82 to 214 mg Zn L-¹ . These thresholds might be more useful for risk assessors working on reclamation sites than those based on non-reclamation species that are widely used.

Zinc oxide nanoparticles (ZnO-NPs) are among the most commonly used nano-fertilizers (NF). However, elevated levels of ZnO-NPs in soil may affect plant growth and development due to its potential toxicity when accumulated in large amounts in plant tissues. This research was conducted using an in situ rhizobox system with the aims of evaluating zinc uptake from nano-zinc oxide amended rhizosphere soil by alfalfa plant and the effect of plant growth-promoting microorganisms on alleviating the phytotoxicity of ZnO-NPs. Treatments included microbial inoculations (Sinorhizobium meliloti, Serendipita indica) and different ZnO-NP concentrations (0, 400, and 800 mg kg⁻¹) with three replications. The results indicated that S. indica minimized the phytotoxicity of ZnO-NPs to alfalfa by enhancing growth rate and decreasing zinc (Zn) translocation from root to shoot. Compared with plants inoculated with S. meliloti, co-inoculation with S. indica increased the shoot dry weight by 18.33% and 8.05% at 400 and 800 mg kg⁻¹ ZnO-NPs, respectively. However, at the highest level of ZnO-NPs (800 mg kg⁻¹), root inoculation of S. indica and S. indica + S. meliloti decreased Zn translocation factor by 60.2% and 44.3% compared to S. meliloti, respectively. Furthermore, a distinct relation between tolerance of S. indica–colonized plant to ZnO-NPs and the ability of S. indica in inhibiting or retarding degradation of polyunsaturated lipids through prevention of excess reactive oxygen species formation was observed. Malondialdehyde content of inoculated plants with S. indica either alone or in combination with S. meliloti was significantly lower than non-inoculated plants (p< 0.01). Zn-induced oxidative stress was mitigated by S. indica through enhanced activities of catalase and peroxidase enzymes. The findings of the present study indicate the potential use of endophytes fungus S. indica for ensuring food safety and security, and human health in heavy metal-polluted soil by reducing the phytoavailability of heavy metals in the aerial parts of the host plants.

Once previous industrial activity has ceased, brownfields are found in urban and suburban environments and managed in different ways ranging from being left untouched to total reconversion. These situations apply to large surface areas often impacted by residual diffuse pollution. Though significant and preventing any sensitive use, residual contamination does not necessarily require treatment. Moreover, conventional treatments show their technical and economic limits in these situations and gentle remediation options such as phytomanagement might appear more relevant to the management of those sites. Thus, these sites face up two major issues: managing moderate contamination levels and providing an alternative use of economic interest. This work proposes to assess a management strategy associating the phytoremediation of organic pollution along with the production of biomass for energy generation production. A 16-week controlled growth experiment was conducted on a soil substrate moderately impacted by multiple pollution (trace elements, mainly Zn and Pb, and hydrocarbons), by associating rhizodegradation with Medicago sativa or biomass production with Robinia pseudoacacia or Alnus incana in monocultures. The effect of a microbial inoculum amendment on the performances of these treatments was also evaluated. Results showed total hydrocarbons (TH), and to a lesser extent polycyclic aromatic hydrocarbons (PAH), concentrations decreased over time, whatever the plant cover. Good biomass production yields were achieved for both tree species in comparison with the control sample, even though R. pseudoacacia seemed to perform better. Furthermore, the quality of the biomass produced was in conformity with the thresholds set by the legislation concerning its use as a renewable energy source.

Polychlorinated biphenyls (PCBs) are ubiquitous and persistent organic pollutants generated exclusively from human sources and found in the environment as several congeners (e.g. Apirolio, produced in Italy and used for electrical transformers). To evaluate the ability of the natural microbial community of historically PCB-contaminated soil to transform or degrade PCBs after fresh contamination through the addition of Apirolio, a microcosm experiment was conducted in a greenhouse for approximately 8 months. Compost and Medicago sativa (alfalfa) were additionally used in the microcosms to stimulate microbial PCB degradation. Chemical analyses were performed to evaluate PCB concentrations in the soil and plant tissue. Changes in the microbial community under the different experimental conditions were evaluated in terms of total abundance, viability, diversity, and activity. Interestingly, the addition of Apirolio did not negatively affect the microbial community but did stimulate the degradation of the freshly added PCBs. The plant and compost co-presence did not substantially increase PCB degradation, but it increased the microbial abundance and activity and the occurrence of α-Proteobacteria and fungi.

Dongmu-1 Medicago sativa seedlings were used as the test material; the variation characteristics soluble protein, soluble sugar, malondialdehyde, proline, chlorophyll, and relative water content were studied under the artificial simulated freeze-thaw (10, 5, 0, − 3, 0, 5, and 10 °C) and combined with deicing salt stress and buffer. The results showed that freeze-thaw and high-salt stress conditions will lead to the damage in the seedling including the membrane system, lipid peroxidation, and severe dehydration. Because of the self-regulating system as well as a certain degree of resistance, the plants can accumulate plenty of substances such as soluble protein, soluble sugar, and proline so as to regulate the osmotic potential. The content of soluble protein, malondialdehyde, soluble sugar, and proline in different treatment groups rose first and then decreased within a freeze-thaw cycle, among which the content of soluble protein reached the maximum value at 0 °C (t3), 20.82, 18.96, and 17.97 mg/g, respectively. The figure for malondialdehyde and proline peaked at − 3 °C (t4) while soluble sugar content peaked at 0 °C (t5). However, during this period, there were no apparent regulations for chlorophyll content and relative water content in each treatment group. Beyond that, due to the different intensity of compound stress, the seedlings showed different adaptability, and the degree of changes in physiological indexes appeared to be combined freeze-thaw and deicing salt stress > single freeze-thaw stress > combined freeze-thaw, deicing salt stress, and buffer, illustrating that buffer can alleviate the degree of the damage from freeze-thaw and deicing salt stress on M. sativa seedlings to some extent.

Microbial food webs tolerate toxic compounds depending on individualistic species resistance and their ability of using alternate food sources. Soil polluted with low-molecular weight volatile organics, such as hexane, diminishes bacterial and fungal communities despite its short residence time. Survival of microbial species depends on perturbation intensity, which in turn restricts resources for amoebae survival in polluted soil. Soil functional recovery from anthropogenic perturbations depends on microbial organic matter (OM) metabolization of pollutants. However, reconfiguration of amoebae community after soil exposure remains largely unknown. A microcosms study was carried out to determine the effects of hexane on the community structure of soil amoebae as well as the importance of Medicago sativa on amoebae community recovering. Hexane had a negative impact on species richness and structure of the amoebae community 24 h after pollution. There was a significant increase in species richness and number of amoebae 30 days after contamination. These two parameters further increased after 60 days from contamination. After 30 days of the initial trophozoites extinction caused by Hexane, M. sativa’s. Root zone showed a significant increase of both species richness and number of individuals. This recovery trend was kept after 60 days when the highest values in species richness and abundance of individuals were shown in both polluted and non-polluted microcosms. In conclusion, M. sativa’s root zone speeds up recovery of the amoebae community structure after pollution exposure.

Acid deposition and temperature variation could lead to changes of physiological characteristics of plants in response to stress. In this paper, Medicago sativa CV. Dongmu–1 was investigated to test the effects of freeze-thaw circle and acid deposition upon the changes of osmotic adjustment substances, biological membrane permeability, and antioxidant enzymes. The experiment was conducted under laboratory conditions, and the seedlings were divided into four groups (group I: no treatment, group II: acid stressed only, group III: freeze-thaw stressed only, group IV: both freeze-thaw and acid stressed). Results indicated that under freeze-thaw circle and acid deposition, the contents of malondialdehyde (MDA) and proline increased respectively by 0.6~203.4 and 19.3~68.8% when compared with group I, while protein content declined by 4.1~31.7%, and the effects were even significant than freeze-thaw-only stressed groups. In the freeze-thaw process, superoxide dismutase (SOD) activity dropped at first and then increased with the increase of temperature, peaking at − 3 °C by 1118.45 U g⁻¹; peroxidase (POD) activity showed a brief rise and declined rapidly below 0 °C. By increasing the potentials of antioxidant enzymes and MDA, the membrane lipid peroxidation inside alfalfa was prevented; meanwhile, several indexes changed adaptively in resisting hurts. Variation of SOD and POD was induced by the defense mechanism, which showed alfalfa’s satisfactory cold resistance and acid tolerance. Further research on acid deposition and freeze-thaw circle would be beneficial for the global cultivation of forage grass.

In this study, 1-year greenhouse pot experiments were conducted to investigate the effect of Phyllobacterium myrsinacearum strain RC6b on the growth and phytoextraction efficiency of heavy metals by a Zn/Cd hyperaccumulator (Sedum alfredii) and alfalfa (Medicago sativa L.) in a co-cropping system. The treated soil sample was collected from a land reclamation site of Pb/Zn mine tailings in Hanzhong City, Shaanxi Province, China. Results showed that, with the inoculation of RC6b, shoot biomass yields of plants were significantly increased by 15.9–20.2 % and 17.2–19.9 % for alfalfa and S. alfredii, respectively, compared to the non-inoculated plants. Biomass yield of alfalfa was higher than that of S. alfredii. RC6b inoculation increased metal concentrations by 18.6–31.2 % (Pb), 23.8–37.5 % (Cd), and 26.4–38.3 % (Zn) in S. alfredii shoots, and by 13.8–24.7 % (Pb), 15.8–26.6 % (Cd), and 24.8–35.6 % (Zn) in alfalfa shoots, respectively. After six consecutive harvests of shoots, RC6b inoculation increased the phytoextraction efficiencies of Pb, Cd, and Zn by shoots of the co-planting system by 16.9, 46.3, and 60.9 %, respectively. Nevertheless, phytoextraction of Cu was not improved by RC6b inoculation. In the co-planting/inoculation system, the percentage removals of metals from soil by the plant shoots were 6.09, 30.97, 11.10, and 1.68 % for Pb, Cd, Zn, and Cu, respectively, after six harvests of shoots. Inoculation with RC6b significantly increased the soil microbial activity and the carbon utilization ability of the soil microbial community.

Grazing animals act as a bioindicator to study the heavy metal status in the pasture lands because excessive amount of toxic metals in the animal diet either disturb their normal activity or deposit the contaminants into their tissues. The aim of this study was to appraise the chromium status in soil and pasture crops with respect to the nutritional requirement of grazing animals. Three different sites were selected to collect soil, forages, and animal samples from District Jhang. All the samples were processed through atomic absorption spectrophotometer to analyze the chromium concentration in them. Chromium concentration was varied as 0.703–4.20 mg/kg in soil, 0.45–2.85 mg/kg in forages, and 0.588–2.37 mg/kg in all collected animal samples. Both the soil and forage samples displayed the maximum chromium concentration in the Capparis decidua, whereas animal samples revealed maximum concentration in animal blood. Results of pollution load index (0.078 to 0.463 mg/kg) exhibited that all the sample values are less than unity while enrichment factor (1.57–8.25mg/kg) showed that significant level of chromium is enriched in these sites. The maximum value of daily intake (0.0007–0.0055mg/kg/day) and health risk index (0.0004–0.00370055mg/kg/day) was observed in the buffalo that feed on the Capparis decidua. Bio-concentration factor (0.398–2.09mg/kg) value was the maximum in the Medicago sativa. It is concluded that all the animal samples showed chromium concentration beyond their standards. Thus, proper measures should be taken to reduce the metal contamination in these areas that ultimately lessen the availability of toxic metals to grazing animals.

Phytoremediation of contaminated soils relies on the ability of plants to stimulate microbial rhizosphere diversity, by releasing root exudates. This work assessed the impact of diesel contamination on soil populations of culturable bacterial groups (fast growing, N₂-fixing, phosphate (P) solubilizing, and lipolytic bacteria), and collembolans under mesocosm conditions with and without the influence Medicago sativa. We set up six treatments sampled initially within 24 h and examined at 4, 8, and 12 months. Bacterial groups were isolated and identified with 16S rRNA sequencing, while collembolans were classified using taxonomic keys. The populations of P-solubilizing and fast-growing bacteria were stimulated after 4 months in the polluted treatments in absence of M. sativa. On the M. sativa treatments, P-solubilizing and lipolytic bacteria increased after 8 months. Stenotrophomonas and Achromobacter were the most predominant bacterial genera. Collembolans mainly belonging to Poduromorpha and Entomobryomorpha orders, were observed in contaminated treatments on the 12th month, while in the uncontaminated control were found at the 4th month. Hydrocarbon degradation was higher than 80% in all treatments after 12 months. Diesel contamination and soil management reduced significantly the collembolan abundance; these organisms may be considered as biological indicators of soil quality and recovery after an event of diesel contamination.