Natural ageing of biochar improves its benefits to soil Pb immobilization and reduction in soil phytotoxicity.

Amendments are good tools for immobilizing metal(loid) and improving phytoremediation success. However, the amendment effect is variable and depends on multiple parameters, including amendment type and ageing. Such an ageing effect is rarely studied. Our study is one of the first focusing on how biochar storage affects its effect on soil properties and metal(loid) immobilization, when biochar was applied alone or in combination with green manure. To answer this, a 33-day pot incubation experiment was set up using contaminated soil, amended with two biochars (differing in ages: old (Bo) and new (Bn)) and/or two green manures (leaves of clover or poplar) and sown with Phaseolus vulgaris (bioindicator plant). Soil pore waters, plant growth and metal(loid) accumulation were evaluated. Biochar reduced soil acidity (Bn: + 0.75 pH unit, Bo: + 0.72 unit) and Pb mobility (Bn: - 42%, Bo: - 50%), while green manures acidified the soil (- 0.30 pH unit) and immobilized Pb only after 10 days (- 44%). All amendments reduced soil phytotoxicity. Moreover, the biochar stored at room temperature for a few years demonstrated better abilities to improve soil properties, particularly for Pb immobilization, than the biochar freshly prepared. Finally, as mixtures maturated, soil parameters changed until about ten days, then tended to stabilize. Therefore, it can be concluded that (1) biochar storage will affect its chemical properties and ameliorate its effects, (2) biochar can ameliorate soil properties and immobilize metal(loid)s, while green manures tended to have adverse effects at first, and (3) soil/amendment mixtures should be left to mature about two weeks before potential plant implementation.

Co-culture of Salix viminalis and Trifolium repens for the phytostabilisation of Pb and As in mine tailings amended with hardwood biochar.

Metal(loid) soil pollution causes environmental and health issues, and thus those sites need to be remediated. This can be done through phytostabilization, in combination with biochar amendment. The objectives were to investigate the potential of Salix viminalis L. associated with Trifolium repens L. for the phytostabilization of biochar-amended contaminated soils by assessing (1) the tolerance of both plants to metal(loid)s, through the biomass production, (2) the concentrations of metal(loid)s in plant parts and (3) the concentrations of metal(loid)s in soil pore water and percolation waters. Results showed that plant growth affected soil pore water Physico-chemical properties and metal(loid) mobility. When comparing the mono- and poly-cultures, although pH was higher with the polyculture than the monoculture, the decrease in Pb mobility did not differ. Moreover, the leachate analysis showed that As concentration in the soil particles leached from the soil was higher in the polyculture condition, while Pb concentration was the highest in the willow vegetated condition. Finally, willow dry weight was not affected by the presence of clover, while clover dry weight was lower when it was grown with willow. In conclusion, the results showed that the willow and clover polyculture was not better than the monoculture of these two species for the phytomanagement of a former mine site amended with biochar.

Effects of Different Biochars, Activated Carbons and Redmuds on the Growth of Trifolium repens and As and Pb Stabilization in a Former Mine Technosol.

Soil pollution by metal(loid)s is an important issue in Europe, as it causes environmental and health problems. Therefore, remediation of these areas is needed. The success of phytoremediation process will depend on the ability of plants to implement, which can require the addition of amendments to the soil in order to improve soil conditions, immobilize pollutant and thus ameliorate plant growth. Amendments that can be used are biochar, activated carbon and redmuds, all of which have previously shown positive outcomes. The objectives of this study were to evaluate the effects of several amendments (biochars, activated carbons and redmuds) on (i) the soil physico-chemical properties of a former mine technosol contaminated by As and Pb, (ii) As and Pb immobilization and (iii) the growth of Trifolium repens. Results showed that amendment addition could ameliorate soil conditions, by reducing soil acidity (pH increased by 1.2 to 1.7 units) and immobilizing pollutants (85 to 99% of Pb immobilized); and improve plant growth (dry weight increased 1.5 to 2.5 times). However, not all amendments were beneficial to the soil and plant. For instance, the L27 activated carbon acidified soil pH, mobilized As and lowered plant growth. This study has allowed us to conclude that amendment effect is dependent on soil type, metal(loid)s and amendment properties, and it is thus necessary to choose the right amendment. Finally, amendments could be combined for better outcomes.

Effect of biochar, iron sulfate and poultry manure application on the phytotoxicity of a former tin mine.

In phytomanagement approach the application of a combination of amendments is an option for remediating arsenic polluted areas and valorized biomass obtained. Various amendments can be used. Biochar has been shown to reduce metal(loid) availability, and increase soil fertility, while iron sulfate has a considerable As binding capacity, and poultry manure is a source of nutrients. A phytotoxicity test was performed by applying the three amendments (2% biochar, 0.15%, 0.30% and 0.45% iron sulfate and 0.4% poultry manure) to a former tin mine technosol, to investigate their effects on (i) soil pore water properties, (ii) metal(loid) immobilization and (iii) Phaseolus vulgaris L. growth, used as a bioindicator. Biochar addition alone did not affect soil properties or plant parameters. However, the addition of iron sulfate acidified the soil, decreased soil pore water As concentrations, and increased the ones of Fe and Pb. It also improved plant growth, and reduced As and Pb aerial and root concentrations. Finally, the addition of poultry manure had no effect on soil and plants. Based on our results, the combination of iron sulfate with biochar may be a solution for reducing soil toxicity of the Abbaretz mining technosol, improving its fertility, and thus ameliorating plant growth.Novelty statement:The work presented in this manuscript describes the effect of amendment application, i.e., biochar, chicken dung and/or iron sulfate, on soil properties, metals availability and dwarf bean growth, plant used as bioindicator.Our results showed that the combination of a low amount of iron sulfate with biochar is the strategy to reduce soil toxicity, improved its fertility and consequently authorizes plant growth.This study is one of the first describing the effects of combined amendments on a mining soil properties with focusing on metal(loid) mobility.

Effects of biochar, ochre and manure amendments associated with a metallicolous ecotype of Agrostis capillaris on As and Pb stabilization of a former mine technosol.

Metal(loid) soil pollution is a major environmental and health issue, requiring these areas to be remediated, for example through phytoremediation processes. In order to allow proper plant establishment and growth, amendments must be applied to highly contaminated and poorly fertile soils. Amendments are diverse, but many studies have shown the beneficial effects of biochar, manure and ochre, although studies on their combined use are scarce. Moreover, no studies have evaluated the effect of these combined amendments on endemic plant growth. Endemic plants growing on contaminated soils showed higher tolerance toward pollutants compared to plants coming from unpolluted areas. Therefore, the aim of the present study was to evaluate both the effect of amendments (single or combined) on the physicochemical properties of a former mining technosol, and the growth and metal(loid) accumulation ability of endemic Agrostis capillaris plants. This study revealed an improvement in the soil physicochemical properties following the application of amendments, with combined amendments showing better results than the application of just one. On top of this, Agrostis plants performed better on the amended technosols, especially the ones receiving manure, due to its high nutrient content. Finally, based on soil properties, plant growth and the metal(loid) accumulation profile, the use of biochar combined with manure seems to be the most appropriate treatment. Indeed, this treatment showed an improvement in both soil fertility and plant growth. Moreover, Agrostis plants grown in these conditions were among those showing higher root metal(loid) concentration associated with a lower translocation toward aerial parts.

Application of amendments for the phytoremediation of a former mine technosol by endemic pioneer species: alder and birch seedlings.

Metal(loid) pollution of soils has important negative effects on the environment and human health. For the rehabilitation of these soils, some eco-innovative strategies, such as phytoremediation, could be chosen. This practice could establish a plant cover to reduce the toxicity of the pollutants and stabilize the soil, preventing soil erosion and water leaching; this technique is called phytoremediation. For this, plants need to be tolerant to the pollutants present; thus, phytoremediation can have better outcomes if endemic species of the polluted area are used. Finally, to further improve phytoremediation success, amendments can be applied to ameliorate soil conditions. Different amendments can be used, such as biochar, a good metal(loid) immobilizer, compost, a nutrient-rich product and iron sulfate, an efficient arsenic immobilizer. These amendments can either be applied alone or combined for further positive effects. In this context, a mesocosm experiment was performed to study the effects of three amendments, biochar, compost and iron sulfate, applied alone or combined to a former mine technosol, on the soil properties and the phytoremediation potential of two endemic species, Alnus sp. and Betula sp. Results showed that the different amendments reduced soil acidity and decreased metal(loid) mobility, thus improving plant growth. Both species were able to grow on the amended technosols, but alder seedlings had a much higher growth compared to birch seedlings. Finally, the combination of compost with biochar and/or iron sulfate and the establishment of endemic alder plants could be a solution to rehabilitate a former mine technosol.

Contrasted tolerance of Agrostis capillaris metallicolous and non-metallicolous ecotypes in the context of a mining technosol amended by biochar, compost and iron sulfate.

Metal(loid) contamination of soil, resulting from the mining activities, is a major issue worldwide, due to its negative effects on the environment and health. Therefore, these contaminated soils need to be remediated. One realistic method is the assisted phytostabilization, which aims at establishing a vegetation cover on the soil that will reduce metal(loid) bioavailability and spreading through the prevention of wind erosion and water leaching. In addition, amendments are applied to improve soil conditions and ameliorate plant growth. In this goal, biochar and compost showed good results in terms of amelioration of soil fertility and reduction in lead bioavailability. However, they usually have a negative effect on arsenic. On the contrary, iron sulfate showed capacity to reduce arsenic mobility through interaction with its iron hydroxides. Finally, the choice of the appropriate plant species is crucial for the success of assisted phytostabilization. One good option is to use endemic species, adapted to the metal(loid) stress, with a fast growth and large shoot and root systems. The aims of this study were to (1) evaluate the effects of applying biochar, compost and iron sulfate, alone or combined, to a former mine soil on the soil properties and Agrostis capillaris growth, and (2) assess the difference between two Agrostis capillaris ecotypes, an endemic metallicolous ecotype and a non-metallicolous ecotype. Results of the mesocosm experiment showed that amendment application improved soil properties, i.e., reduced soil acidity, increased nutrient availability and lower metal(loid) stress, the best being the combination biochar-compost-iron sulfate. These ameliorations allowed a better plant growth. Finally, the metallicolous ecotype performed better in terms of growth than the non-metallicolous one and could thus be used in an assisted phytostabilization process on the former mine site.

Effect of biochar and redmud amendment combinations on Salix triandra growth, metal(loid) accumulation and oxidative stress response.

Remediation of metal(loid) polluted soils is an important area of research nowadays. In particular, one remediation technique is much studied, phytomanagement. Phytomanagement combines amendment application and plant growth in order to reduce the risk posed by contaminants. Salicaceae plants showed tolerance towards metal(loid)s and the ability to accumulate high amounts of metal(loid)s in their tissue. Amendments are often applied to counterbalance the reduced soil fertility and high metal(loid) concentrations. Two amendments gathered attention over the last decades, biochar (product of biomass pyrolysis), which can be activated for better effects, and redmud (by-product of alumina production). Those two amendments showed ability to improve soil conditions and thus plant growth, although few studied their combined application. Moreover, since metal(loid)s are known to induce the overproduction of reactive oxygen species, it is important to measure the level of oxidative stress in the plant, to which plants respond using enzymatic and non-enzymatic systems. But no studies evaluate the response of Salicaceae plants to metal(loid) stress and amendment application at the biochemical level in a real soil condition. Therefore, a mesocosm study was set up to evaluate the effect of amending a mine soil with redmud combined to diverse biochars on the soil properties and Salix triandra growth, metal(loid) accumulation and stress marker levels. Results showed that all amendment combinations improved the soil fertility, reduced metal(loid) mobility and thus ameliorated Salix triandra growth, which accumulated metal(loid)s mainly in its roots. Moreover, among the different amendment combinations, Salix triandra plants still suffered from oxidative stress when grown on PG soil amended with redmud and chemical activated carbon, showing elevated levels of phenolic compounds and salicinoids and important antioxidant and enzymatic activities. Finally, one treatment showed levels of these stress markers similar or lower than the control, the combination of redmud with steam activated carbon. In conclusion, this treatment seemed a good solution in a phytomanagement strategy using Salix triandra, improving soil conditions and plant growth and reducing oxidative stress level in the plant roots.

Application of biochars and solid fraction of digestate to decrease soil solution Cd, Pb and Zn concentrations in contaminated sandy soils.

Biochar prepared from waste biomass was evaluated as a soil amendment to immobilize metals in two contaminated soils. A 60-day incubation experiment was set up on a French technosol which was heavily contaminated with Pb due to former mining activities. Grass biochar, cow manure biochar (CMB) and two lightwood biochars differing in particle size distribution (LWB1 and LWB2) were amended to the soil at a rate of 2% (by mass). Rhizon soil moisture samplers were employed to assess the Pb concentrations in the soil solution at regular times. After 30 days of incubation, soil solution concentrations in the CMB-amended soil decreased by more than 99% compared to the control. CMB was also applied to a moderately contaminated Flemish soil and resulted in lowered soil solution Cd and Zn concentrations. While the application of 4% CMB resulted in 90% and 80% reductions in soil solution concentrations of Cd and Zn, respectively, the solid fraction of digestate (as a reference) reduced the soil pore water concentrations by only 63% for Cd and 73% for Zn, compared to the concentrations in the control. These results emphasize the potential of biochar to immobilize metals in soil and water systems, thus reducing their phytotoxicity.

Mobility of Pb, Zn, Ba, As and Cd toward soil pore water and plants (willow and ryegrass) from a mine soil amended with biochar.

Mine soils often contain metal(loid)s that may lead to serious environmental problems. Phytoremediation, consisting in covering the soil with specific plants with the possible addition of amendments, represents an interesting way of enhancing the quality of mine soils by retaining contaminants and reducing soil erosion. In order to study the effect of an assisted phytoremediation (with willow and ryegrass) on the properties of soil pore water (SPW), we investigated the impact of amendment with biochar (BC) combined with the planting of willow and ryegrass on the behavior of several metal(loid)s (Pb, Zn, Ba, As, and Cd) in a mine soil. Data on the physicochemical parameters and concentrations of the different metal(loid)s in both SPW and in plant tissues of willow and ryegrass highlight the importance of BC for SPW properties in terms of reductions in soluble concentrations of Pb and Zn, although there was no effect on the behavior of As and Cd. BC also increased soluble concentrations of Ba, probably related to ion release by the BC. By improving major ions available in mine soil, BC improved the lifetime of plants and enhanced their growth. Plant development did not appear to significantly affect the physicochemical parameters of SPW. Willow and ryegrass growing on soil with BC incorporated Cd and Ba into their tissues. The influence of plants on the behavior of metal(loid)s was noticeable only for ryegrass growing in soil with 2% BC, where it modified the behavior of Pb and Ba.

The Hevea brasiliensis XIP aquaporin subfamily: genomic, structural and functional characterizations with relevance to intensive latex harvesting.

X-Intrinsic Proteins (XIP) were recently identified in a narrow range of plants as a full clade within the aquaporins. These channels reportedly facilitate the transport of a wide range of hydrophobic solutes. The functional roles of XIP in planta remain poorly identified. In this study, we found three XIP genes (HbXIP1;1, HbXIP2;1 and HbXIP3;1) in the Hevea brasiliensis genome. Comprehensive bioinformatics, biochemical and structural analyses were used to acquire a better understanding of this AQP subfamily. Phylogenetic analysis revealed that HbXIPs clustered into two major groups, each distributed in a specific lineage of the order Malpighiales. Tissue-specific expression profiles showed that only HbXIP2;1 was expressed in all the vegetative tissues tested (leaves, stem, bark, xylem and latex), suggesting that HbXIP2;1 could take part in a wide range of cellular processes. This is particularly relevant to the rubber-producing laticiferous system, where this isoform was found to be up-regulated during tapping and ethylene treatments. Furthermore, the XIP transcriptional pattern is significantly correlated to latex production level. Structural comparison with SoPIP2;1 from Spinacia oleracea species provides new insights into the possible role of structural checkpoints by which HbXIP2;1 ensures glycerol transfer across the membrane. From these results, we discuss the physiological involvement of glycerol and HbXIP2;1 in water homeostasis and carbon stream of challenged laticifers. The characterization of HbXIP2;1 during rubber tree tapping lends new insights into molecular and physiological response processes of laticifer metabolism in the context of latex exploitation.

Exploring Phytoremediation Potential: A Comprehensive Study of Flora Inventory and Soil Heavy Metal Contents in the Northeastern Mining Districts of Morocco.

Mining activities produce waste materials and effluents with very high metal concentrations that can negatively impact ecosystems and human health. Consequently, data on soil and plant metal levels are crucial for evaluating pollution severity and formulating soil reclamation strategies, such as phytoremediation. Our research focused on soils and vegetation of a highly contaminated site with potentially toxic metals (Pb, Zn, and Cu) in the Touissit mining districts of eastern Morocco. Vegetation inventory was carried out in three mine tailings of the Touissit mine fields using the "field tower" technique. Here, 91 species belonging to 23 families were inventoried: the most represented families were Poaceae and Asteraceae, and the biological spectrum indicated a predominance of Therophytes (55.12%). From the studied areas, 15 species were selected and collected in triplicate on the tailings and sampled with their corresponding rhizospheric soils, and analyzed for Pb, Zn, and Cu concentrations. Reseda lutea, lotus marocanus, and lotus corniculatus can be considered as hyperaccumulators of Pb, as these plants accumulated more than 1000 mg·kg-1 in their aerial parts. According to TF, these plant species could serve as effective plants for Pb phytoextraction.

Importance of Application Rates of Compost and Biochar on Soil Metal(Loid) Immobilization and Plant Growth.

In this study, we investigated the effect of different rates of compost (20%, 40%, 60% w/w) in combination with biochar (0%, 2%, 6% w/w) on soil physiochemical properties and the mobility of arsenic (As) and lead (Pb), in addition to the ability of Arabidopsis thaliana (ecotype Columbia-0) to grow and accumulate metal(loid)s. All modalities improved pH and electrical conductivity, stabilized Pb and mobilized As, but only the mixture of 20% compost and 6% biochar improved plant growth. Plants in all modalities showed a significant reduction in root and shoot Pb concentrations compared to the non-amended technosol. In contrast, As shoot concentration was significantly lower for plants in all modalities (except with 20% compost only) compared to non-amended technosol. For root As, plants in all modalities showed a significant reduction except for the mixture of 20% compost and 6% biochar. Overall, our results indicate that the mixture of 20% compost with 6% biochar emerged as the optimum combination for improving plant growth and As uptake, making it the possible optimum combination for enhancing the efficiency of land reclamation strategies. These findings provide a foundation for further research on the long-term effects and potential applications of the compost-biochar combination in improving soil quality.

Different species of Bradyrhizobium from symbiovars genistearum and retamae nodulate the endemic Retama dasycarpa in the High Atlas Mountains.

Retama dasycarpa is an endemic Retama species native to the cold semi-arid bioclimates of the High Atlas Mountains in Morocco. In this work, we analyzed the diversity of the microsymbionts nodulating this plant and their different phenotypic and symbiotic characteristics. Phylogenetic analysis of the 16S rRNA gene revealed that the tested isolates clustered in the Bradyrhizobium genus. Multilocus sequence analyses of four housekeeping genes (recA, gyrB, glnII and atpD) for 12 selected strains grouped them into four clusters close to B. lupini USDA 3051T, B. frederickii CNPSo 3446T, B. valentinum LmjM3T and B. retamae Ro19T. The individual phylogenies of these core genes and the symbiotic genes nodC, nodA and nifH were congruent. These isolates showed a broad host range, being able to nodulate different legume hosts, such as R. sphaerocarpa, R. monosperma, Lupinus luteus, Cytisus grandiflorus andChamaecytisus albidus, but not Phaseolus vulgaris or Glycine max. They all had a similar metabolic capacity, using the majority of the carbohydrates and amino acids tested as sole sources of carbon and nitrogen. Furthermore, out of the 12 selected strains, some displayed plant growth-promoting features, with six of them solubilizing phosphate and three of them producing siderophores. The present work provides, for the first time, a detailed description about the microsymbionts associated with the endemic legume R. dasycarpa.

The reduction of the As and Pb phytotoxicity of a former mine technosol depends on the amendment type and properties.

In remediation of metal(loid) polluted soils, it is crucial to improve soil conditions and reduce metal(loid) toxicity to permit plant growth. To do that, amendments, such as biochar, activated carbon, and redmud, can be applied to the soil. Their effects are dependent on their type and properties. The aims of this study were thus to evaluate the potential of diverse biochars, activated carbons, and redmuds to reduce phytotoxicity of a former mine technosol polluted with As and Pb. Two pots experiments were set up. The first one applied on Pontgibaud technosol ten biochars, eight activated carbons, and three redmuds, at 2% for the biochars and activated carbons and 1% for the redmud. Soil pore water properties (pH, electrical conductivity), metal(loid) mobility, and Phaseolus vulgaris growth were monitored. In a second experiment, the five best amendments, one redmud associated with two biochars and two activated carbons, selected based on their ability to improve soil conditions, immobilize metal(loid)s and improve plant growth, were applied. The same plant species was used and soil and plant parameters were measured. Results demonstrated that not all amendments were capable of ameliorating soil conditions and reducing soil phytotoxicity. Moreover, the five selected amendments (biochars from oak bark sapwood and bamboo, activated carbons from vegetal feedstock chemically activated and physically activated, modified redmud) showed good sorption capacity towards Pb, with maximum sorption capacity between 63 and 217 mg g-1, depending on the amendment, and their combined application led to better soil properties improvement than the single amendments. However, plant growth was only ameliorated further than a single application in the redmud-biochar combination but not in the association of redmud with activated carbon. This study is one of the first to deliver a rapid phytotoxicity test screening demonstrating that redmud associated with particular biochar could be beneficial in reducing the phytotoxicity of technosol polluted with As and Pb and thus allow plant growth and a phytomanagement process.

The Potential of Clover Green Amendment, Associated with Biochar, Activated Carbon or Ochre, for the Phytoremediation, Using Populus x. canescens, of a Former Mine Technosol.

Metal(loid) soil pollution resulting from past and present mine activities is a serious environmental and health issues worldwide. Therefore, the remediation of those polluted areas has been a growing research interest over the last decades, especially the assisted phytoremediation. In this study, a pot experiment was set up, using a former mine technosol, highly polluted by As and Pb, to which biochar, activated carbon, or ochre was applied, alone or in combination to clover green amendment. Following amendment application, Populus x. canescens cuttings were planted. Results showed that all four amendments reduced soil acidity. However only the first three amendments immobilized As and Pb, while the green amendment drastically mobilized those two pollutants and none of the amendments improved plant growth. In conclusion, the association of clover green amendment to biochar, activated carbon, or ochre did not appear as an efficient remediation strategy in this case; although the aging of the amendments and degradation of the green amendment in the soil with time could have positive outcomes.

Rehabilitation of mine soils by phytostabilization: Does soil inoculation with microbial consortia stimulate Agrostis growth and metal(loid) immobilization?

Metal(loid) soil pollution resulting from mining activities is an important issue that has negative effects on the environment (soil acidification, lack of vegetation, groundwater pollution) and human health (cancer, chronic diseases). In the context of a phytostabilization process for the bioremediation of a mine soil highly contaminated by arsenic (As) and lead (Pb), a pot experiment was set up to study the effect of plant sowing and microbial inoculation on soil properties, metal(loid) (im)mobilization in soil and accumulation in plant, and plant growth. For this, mine soil was sown with endemic metallicolous Agrostis seeds and/or inoculated with endogenous microbial consortia previously selected for their As and Pb tolerance. Agrostis was able to develop on the contaminated mine soil and immobilized metal(loid)s through metal(loid) accumulation in the roots. Its growth was improved by microbial consortium inoculation. Moreover, microbial consortium inoculation increased soil organic content and electrical conductivity, and led to an increase in soil microbial activities (linked to C and P cycles); however, it also induced a metal(loid) mobilization. In conclusion, microbial consortium inoculation stimulated the growth of endemic Agrostis plants and thus ameliorated the phytostabilization of a former mine soil highly polluted by As and Pb. This study is thus a good example of the benefits of coupling several approaches such as phytostabilization and bioaugmentation for the bioremediation of former mine contaminated sites.

Physiological and molecular responses of flax (Linum usitatissimum L.) cultivars under a multicontaminated technosol amended with biochar.

Soil pollution is a worldwide issue and has a strong impact on ecosystems. Metal(loid)s have toxic effects on plants and affect various plant life traits. That is why metal(loid) polluted soils need to be remediated. As a remediation solution, phytoremediation, which uses plants to reduce the toxicity and risk of polluted soils, has been proposed. Moreover, flax (Linum usitatissimum L.) has been suggested as a potential phytoremediation plant, due to its antioxidant systems, which can lower the production of reactive oxygen species and can also chelate metal(loid)s. However, the high metal(loid) toxicity associated with the low fertility of the polluted soils render vegetation difficult to establish. Therefore, amendments, such as biochar, need to be applied to improve soil conditions and immobilize metal(loid)s. Here, we analyzed the growth parameters and oxidative stress biomarkers (ROS production, membrane lipid peroxidation, protein carbonylation and 8-oxoGuanine formation) of five different flax cultivars when grown on a real contaminated soil condition, and in the presence of a biochar amendment. Significant correlations were observed between plant growth, tolerance to oxidative stress, and reprogramming of phytochemical accumulation. A clear genotype-dependent response to metal(loid) stress was observed. It was demonstrated that some phenylpropanoids such as benzoic acid, caffeic acid, lariciresinol, and kaempferol played a key role in the tolerance to the metal(loid)-induced oxidative stress. According to these results, it appeared that some flax genotypes, i.e., Angora and Baikal, could be well adapted for the phytoremediation of metal(loid) polluted soils as a consequence of their adaptation to oxidative stress.

The rhizosphere of Salix viminalis plants after a phytostabilization process assisted by biochar, compost, and iron grit: chemical and (micro)-biological analyses.

Amendments, such as biochar, compost, and iron grit, used in phytostabilization studies, showed positive effects on soil physico-chemical properties, plant growth, and the microbial community. However, assisted phytostabilization studies do not always focus on the rhizosphere area where soil, plants, and microorganisms are affected by the amendments and plants and microorganisms can also interact with each other. The aims of this study were to evaluate the effects of amendment application on the exudation of organic acids by Salix viminalis plant roots, as well as the effects of amendments and plant development on the soil CHNS contents and the microbial community activity and diversity, assessed by measuring enzyme activities and using Biolog EcoPlatesTM tests and next-generation sequencing analyses. The results of the mesocosm experiment showed that soil C, H, and N contents were increased by amendment application, especially biochar and compost, while the one of S decreased. Enzyme activities, microbial activity, and diversity were also increased by the addition of amendments, except iron grit alone. Finally, the quantity of organic acids exuded by roots were little affected by amendments, which could in part explain the reduced effect of plant development on soil chemical and microbiological parameters. In conclusion, this study showed in particular that biochar and compost were beneficial for the soil CHN contents and the microbial community while affecting poorly Salix viminalis root exudates.

Evaluation of direct and biochar carrier-based inoculation of Bacillus sp. on As- and Pb-contaminated technosol: effect on metal(loid) availability, Salix viminalis growth, and soil microbial diversity/activity.

Phytomanagement manipulates the soil-plant system to lower the risk posed by contaminated soils. In this process, the addition of amendments, such as biochar, and bacteria can improve the fertility of poor contaminated soils and consequently ameliorate plant growth. A number of studies based on the inoculation of soil with microorganisms of the genus Bacillus, previously isolated from contaminated sites, revealed positive effects on soil properties and plant growth. Furthermore, when the Bacillus isolates were used in association with biochar, better results were obtained, as biochar can ameliorate soil properties and serve as habitat for microorganisms. Accordingly, a mesocosm study was set-up using a mining technosol amended with biochar and inoculated with an endogenous Bacillus isolate, to evaluate the effect of inoculation on soil properties, metal(loid) immobilization, and Salix viminalis growth. Two inoculation methods were compared: (1) direct inoculation of bacteria (Bacillus sp.) and (2) inoculation using biochar as a carrier. Results showed that the Bacillus isolate modified soil properties and ameliorated plant growth, while having a reduced effect on metal(loid) accumulation. The microbial activity was also stimulated, and the community composition was shifted, more importantly when biochar was used as a carrier. In conclusion, this research revealed an improvement of the plant growth and microbial activity after the addition of the endogenous bacterium to the analyzed former mining soil, with better results recorded when a carrier was used.