Contrasting effects of biochar, compost and farm manure on alleviation of nickel toxicity in maize (Zea mays L.) in relation to plant growth, photosynthesis and metal uptake

Elucidating the role of rice straw biochar in modulating Helianthus annuus L. antioxidants, secondary metabolites and soil post-harvest characteristics in different types of microplastics

The emergence of microplastics (MPs) as pollutants in agricultural soils is increasingly alarming, presenting significant threats to soil ecosystems. Given the widespread contamination of ecosystems by various types of MPs, including polystyrene (PS), polyvinyl chloride (PVC), and polyethylene (PE), it is crucial to understand their effects on agricultural productivity. The present study was conducted to investigate the effects of different types of MPs (PS, PVC, and PE) on various aspects of sunflower (Helianthus annuus L.) growth with the addition of rice straw biochar (RSB). This study aimed to examine plant growth and biomass, photosynthetic pigments and gas exchange characteristics, oxidative stress indicators, and the response of various antioxidants (enzymatic and non-enzymatic) and their specific gene expression, proline metabolism, the AsA-GSH cycle, cellular fractionation in the plants and post-harvest soil properties. The research outcomes indicated that elevated levels of different types of MPs in the soil notably reduced plant growth and biomass, photosynthetic pigments, and gas exchange attributes. Different types of MPs also induced oxidative stress, which caused an increase in various enzymatic and non-enzymatic antioxidant compounds, gene expression and sugar content; notably, a significant increase in proline metabolism, AsA-GSH cycle, and pigmentation of cellular components was also observed. Favorably, the addition of RSB significantly increased plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds, and relevant gene expression while decreasing oxidative stress. In addition, RSB amendment decreased proline metabolism and AsA-GSH cycle in H. annuus plants, thereby enhancing cellular fractionation and improving post-harvest soil properties. These results open new avenues for sustainable agriculture practices and show great potential for resolving the urgent issues caused by microplastic contamination in agricultural soils.

Effect of soil additives on biogeochemistry of ultramafic soils-an experimental approach with Brassica napus L

Ultramafic soils are characterized by low productivity due to the deficiency of macroelements and high content of Ni, Cr, and Co. Incorporation of ultramafic soils for agricultural and food production involves the use of fertilizers. Therefore, this study aims to find the soil additive that decreases the metallic elements uptake by plant using Brassica napus as an example. In this study, we evaluate the effect of manure (0.5 g N/kg of soil), humic acids (1 g of Rosahumus/1 dm3 H2O; 44% C), KNO3 (0.13 g K/kg of soil), lime (12.5 g/kg of soil), (NH4)2SO4 (0.15 g N/kg of soil), and Ca(H2PO4)2) (0.07 g P/kg of soil) on the phytoavailability of metallic elements. The effect of soil additives on metallic elements uptake by Brassica napus was studied in a pot experiment executed in triplicates. Statistical analysis was applied to compare the effects of additives in ultramafic soil on plant chemical composition relative to control unfertilized ultramafic soil (one-way ANOVA and Kruskal-Wallis test). The study shows that in almost all treatments, metallic elements content (Ni, Cr, Co, Al, Fe, Mn) is higher in roots compared to the aboveground parts of Brassica napus except for (NH4)2SO4, in which the mechanism of Mn accumulation is opposite. The main differences between the treatments are observed for the buffer properties of soil and the accumulation of specific metals by studied plants. The soils with the addition of lime and manure have the highest buffer properties in acidic conditions (4.9-fold and 2.1-fold increase relative to control soil, respectively), whereas the soil with (NH4)2SO4 has the lowest effect (0.8-fold decrease relative to control soil). Also, the addition of manure increases the biomass of aboveground parts of B. napus (3.4-fold increase) and decreases the accumulation of Ni (0.6-fold decrease) compared to plants cultivated in the control soil. On the contrary, the addition of (NH4)2SO4 noticeably increases the accumulation of Ni, Co, Mn, and Al in aboveground parts of B. napus (3.2-fold, 18.2-fold, 11.2-fold, and 1.6-fold, respectively) compared to plant grown in control soil, whereas the humic acids increase the accumulation of Cr in roots (1.6-fold increase). Therefore, this study shows that manure is a promising fertilizer in agricultural practices in ultramafic soil, whereas (NH4)2SO4 and humic acids must not be used in ultramafic areas.

Synergistic effect by Sorghum bicolor L., citric acid, biochar, and vermiwash amendment for the remediation of a mine-contaminated soil

Phytoremediation is an in situ remediation and eco-friendly technique employing accumulator plant species to remove trace elements (TEs) from contaminated sites. Moreover, it has been demonstrated that both natural and synthetic amendments can enhance trace elements (TEs) phytoremediation from polluted soils through bioenergy crops. This work assessed the synergistic impact of two tested biochar (BC) from data palm (B1) and Prosopis (B2) (1.5%/ kg), citric acid (CA, 1.5 mmol/kg) and vermiwash (VW, 20 ml/kg) to enhance the remediation of tested TEs (Mn, Zn, Cd, Pb, Ni, Cu, and Fe) from Mahad AD'Dahab mine-contaminated soil by sorghum (Sorghum bicolor L.). The BC and CA amendments alone and combined with VW significantly augmented the proliferation and survival of sorghum grown in mine-contaminated soil. Considering the individual and combined applications of VW and BC, the influence on plant growth followed this order: K < VW < B2 < B1 < B1 + VW < B2 + VW < CA < CA + VW. Applying tested BC/CA and VW significantly increased chlorophyll compared to unamended soil. The outcomes revealed a substantial elevation in TE absorption in both shoot and root (p ≤ 0.05) with all tested treatments compared to the untreated soil (K). The combined application of CA and VW resulted in the most significant TE uptake of TEs at both the root and the shoot. Furthermore, adding CA or VW as a foliar spray enhanced the bioaccumulation factor (BCF) and translocation factor (TF) of studied metals. The combined addition of CA and foliar spraying of VW was more effective than the sole addition of CA or VW. Such increase reached 20.0%, 15.6%, 19.4%, 14.3%, 14.0%, and 25.6% of TF, and 13.7%, 11.9%, 8.3%, 20.9%, 20.5%,18.7%, and 19.8% of BCE for Cd, Cu, Fe, Mn, Ni, Pb, and Zn, respectively. This study highlights the efficiency of combining CA/BC with VW as a more viable option for remediating mine-contaminated soil than individual amendments. However, future research should prioritize long-term field trials to assess the efficiency of using citric acid and vermiwash for restoring contaminated mining soils.

An assessment of nanotechnology-based interventions for cleaning up toxic heavy metal/metalloid-contaminated agroecosystems: Potentials and issues

Heavy metals (HMs) are among the most dangerous environmental variables for a variety of life forms, including crops. Accumulation of HMs in consumables and their subsequent transmission to the food web are serious concerns for scientific communities and policy makers. The function of essential plant cellular macromolecules is substantially hampered by HMs, which eventually have a detrimental effect on agricultural yield. Among these HMs, three were considered, i.e., arsenic, cadmium, and chromium, in this review, from agro-ecosystem perspective. Compared with conventional plant growth regulators, the use of nanoparticles (NPs) is a relatively recent, successful, and promising method among the many methods employed to address or alleviate the toxicity of HMs. The ability of NPs to reduce HM mobility in soil, reduce HM availability, enhance the ability of the apoplastic barrier to prevent HM translocation inside the plant, strengthen the plant's antioxidant system by significantly enhancing the activities of many enzymatic and nonenzymatic antioxidants, and increase the generation of specialized metabolites together support the effectiveness of NPs as stress relievers. In this review article, to assess the efficacy of various NP types in ameliorating HM toxicity in plants, we adopted a 'fusion approach', in which a machine learning-based analysis was used to systematically highlight current research trends based on which an extensive literature survey is planned. A holistic assessment of HMs and NMs was subsequently carried out to highlight the future course of action(s).

Synergistic effect of biochar with gypsum, lime, and farm manure on the growth and tolerance in rice plants under different salt-affected soils

Soil salinization and sodication harm soil fertility and crop production, especially in dry regions. To combat this, using biochar combined with gypsum, lime, and farm manure is a promising solution for improving salt-affected soils. In a pot experiment, cotton stick biochar (BC) was applied at a rate of 20 t/ha in combination with gypsum (G), lime (L), and farm manure (F) at rates of 5 and 10 t/ha. These were denoted as BCG-5, BCL-5, BCF-5, BCG-10, BCL-10, and BCF-10. Three different types of soils with electrical conductivity (EC) to sodium adsorption ratio (SAR) ratios of 2.45:13.7, 9.45:22, and 11.56:40 were used for experimentation. The application of BCG-10 led to significant improvements in rice biomass, chlorophyll content, and overall growth. It was observed that applying BCG-10 to soils increased the membrane stability index by 75% in EC:SAR (2.45:13.7), 97% in EC:SAR (9.45:22), and 40% in EC:SAR (11.56:40) compared to respective control treatments. After BCG-10 was applied, the hydrogen peroxide in leaves dropped by 29%, 23%, and 21% in EC:SAR (2.45:13.7), EC:SAR (9.45:22), and EC:SAR (11.56:40) soils, relative to their controls, respectively. The application of BCG-10 resulted in glycine betaine increases of 60, 119, and 165% in EC: SAR (2.45:13.7), EC: SAR (9.45:22), and EC: SAR (11.56:40) soils. EC: SAR (2.45:13.7), EC: SAR (9.45:22), and EC: SAR (11.56:40) soils all had 70, 109, and 130% more ascorbic acid in BCG-10 applied treatment, respectively. The results of this experiment show that BCG-10 increased the growth and physiological traits of rice plants were exposed to different levels of salt stress. This was achieved by lowering hydrogen peroxide levels, making plant cells more stable, and increasing non-enzymatic activity.

Elevated atmospheric CO2 combined with Epichloë endophyte may improve growth and Cd phytoremediation potential of tall fescue (Festuca arundinacea L.)

Complex environmental conditions like heavy metal contamination and elevated CO2 concentration may cause numerous plant stresses and lead to considerable crop losses worldwide. Cadmium is a non-essential element and potentially highly toxic soil metal pollution, causing oxidative stress in plants and human toxicity. In order to assess a combination of complex factors on the responses of two genotypes of Festuca arundinacea (75B and 75C), a greenhouse experiment was conducted on plants grown in two Cd-contaminated soil conditions and two soil textures under combined effects of elevated ambient CO2 (700 ppm) and Epichloë endophyte infection. Plant biomass, Cd, Fe, Cu, Zn, and Mn concentrations in the plant shoots and roots, Fv/Fm, chlorophyll (a & b), and carotenoid contents were measured after 7 months of growth in pots. Our results showed that endophyte-infected plants (E+) grown in elevated CO2 atmosphere (CO2+), clay-loam soil texture (H) with no Cd amendment (Cd-) in the genotype 75B had significantly greater shoot and root biomass than non-infected plants (E-) grown in ambient CO2 concentration (CO2-), sandy-loam soil texture (L) with amended Cd (Cd+) in the genotype 75C. Increased CO2 concentration and endophyte infection, especially in the genotype 75B, enabled Festuca for greater phytoremediation of Cd because of higher tolerance to Cd stress and higher biomass accumulation in the plant genotype. However, CO2 enrichment negatively influenced the plant mineral absorption due to the inhibitory effects of high Cd concentration in shoots and roots. It is concluded that Cd phytoremediation can be positively affected by the increased atmospheric CO2 concentration, tolerant plant genotype, heavy soil texture, and Epichloë endophyte. Using Taguchi and AIC design methodologies, it was also predicted that the most critical factors affecting Cd phytoremediation potential were CO2 concentration and plant genotype.

Investigation of interaction effects of biochars and silicon on growth and chemical composition of Zea mays L. in a Ni-polluted calcareous soil

Biochars are cost effective, carbonaceous amendments that can immobilize potentially toxic elements (PTEs) in soils. Application of silicon (Si) has been shown to mitigate the effect of soil PTEs on plants. Studies on the interaction effects of Si and biochars in PTE-contaminated soils are limited. Thus, the aim of this study was to investigate the interaction effects of biochars, from sheep manure (SMB) and rice husk (RHB) produced at 300 and 500 °C, and 2 levels of Si (as sodium (Na) metasilicate), on growth and chemical composition of corn (Zea mays) in a nickel (Ni)-polluted calcareous soil. The combined application of Si and biochars significantly reduced soil available Ni (17-32%) and the corn shoot Ni concentrations (29-58%), associated with soil pH increase (r = 0.56-0.60, P < 0.01). Application of SMB resulted in greater soil pH increases compared to RHB, and increased soil electrical conductivity (EC) to saline levels, attributed to its higher ash content. Increasing Si application levels also increased soil pH and EC values. Application of all the biochars resulted in significant biomass increases, with RHB having the most positive effect. Despite the positive effect on soil Ni immobilization, the combined application of Si and biochars generally resulted in a decrease in corn shoot biomass yields compared to biochars alone. The biomass decrease was attributed to the significantly higher soil sodicity and pH in the combined treatments which resulted in suppression of macro and micronutrient uptake by the corn. Although the combination of biochar and Na metasilicate was effective at immobilizing soil Ni, future studies should rather employ other essential basic cation metasilicates.

Risk assessment of toxic and hazardous metals in paddy agroecosystem by biochar-for bio-membrane applications

Toxic and carcinogenic metal (loid)s, such arsenic (As) and cadmium (Cd), found in contaminated paddy soils pose a serious danger to environmental sustainability. Their geochemical activities are complex, making it difficult to manage their contamination. Rice grown in Cd and As-polluted soils ends up in people's bellies, where it can cause cancer, anemia, and the deadly itai sickness. Solving this issue calls for research into eco-friendly and cost-effective remediation technology to lower rice's As and Cd levels. This research delves deeply into the origins of As and Cd in paddy soils, as well as their mobility, bioavailability, and uptake mechanisms by rice plants. It also examines the current methods and reactors used to lower As and Cd contamination in rice. Iron-modified biochar (Fe-BC) is a promising technology for reducing As and Cd toxicity in rice, improving soil health, and boosting rice's nutritional value. Biochar's physiochemical characteristics are enhanced by the addition of iron, making it a potent adsorbent for As and Cd ions. In conclusion, Fe-BC's biomembrane properties make them an attractive option for remediating As- and Cd-contaminated paddy soils. More efficient mitigation measures, including the use of biomembrane technology, can be developed when sustainable agriculture practices are combined with these technologies.

Nickel (Ni) phytotoxicity and detoxification mechanisms: A review

Scientists studying the environment, physiology, and biology have been particularly interested in nickel (Ni) because of its dual effects (essentiality and toxicity) on terrestrial biota. It has been reported in some studies that without an adequate supply of Ni, plants are unable to finish their life cycle. The safest Ni limit for plants is 1.5 μg g^-1, while the limit for soil is between 75 and 150 μg g^-1. Ni at lethal levels harms plants by interfering with a variety of physiological functions, including enzyme activity, root development, photosynthesis, and mineral uptake. This review focuses on the occurrence and phytotoxicity of Ni with respect to growth, physiological and biochemical aspects. It also delves into advanced Ni detoxification mechanisms such as cellular modifications, organic acids, and chelation of Ni by plant roots, and emphasizes the role of genes involved in Ni detoxification. The discussion has been carried out on the current state of using soil amendments and plant-microbe interactions to successfully remediate Ni from contaminated sites. This review has identified potential drawbacks and difficulties of various strategies for Ni remediation, discussed the importance of these findings for environmental authorities and decision-makers, and concluded by noting the sustainability concerns and future research needs regarding Ni remediation.

The beneficial effects of bare and CMC-supported α-FeOOH, Fe3O4, and α-Fe2O3 nanoparticles on growth, nutrient content, and essential oil of summer savory (Satureja hortensis L.) under Cd, Pb and Zn stresses

This research studies the impacts of iron oxide nanoparticles (FeONPs) on alleviating the toxic effects of cadmium (Cd), lead (Pb), and zinc (Zn) on summer savory (Satureja hortensis L.). Different types of soil additives, including bare and carboxymethylcellulose (CMC)-supported hematite (α-Fe₂O₃), goethite (α-FeOOH), and magnetite (Fe₃O₄), were applied at three rates (0, 0.25, and 0.5% w/w) to a Cd, Pb, and Zn-contaminated soil sample. The experimental results showed that the application of FeONPs increased plant height, dry weights of shoot and root, and yield and content of essential oil. Bare and CMC-supported FeONPs increased the content of K, P, and Fe in the aerial parts of summer savory. However, these soil additives reduced the contents of Cd, Pb, and Zn in plant tissues. CMC-supported FeONPs proved to be more efficient additives in diminishing the toxic effects of Cd, Pb, and Zn in summer savory compared to their bare forms. Bare and CMC-supported goethite NPs were able to restrict the uptake of Cd, Pb, and Zn by summer savory roots in the metal-contaminated soil. The application of CMC-supported goethite at an application dose of 0.5% (w/w) increased shoot dry weight, shoot concentrations of K, P, and Fe, and yield of essential oil by about 62.6, 76.6, 77.1, 210, and 230%, respectively. Conversely, they reduced shoot concentrations of Cd, Pb, and Zn by about 64.6, 68.7, and 40.6%, respectively, compared to the control. These are significant results and indicate that CMC-supported goethite is likely to be the most effective soil additive in diminishing the toxicity of Cd, Pb, and Zn to metal-stressed summer savory.

Aquaculture sediments amended with biochar improved soil health and plant growth in a degraded soil

Sustainable and safe management of aquaculture sediments is of great concern. Biochar (BC) and fishpond sediments (FPS) are rich in organic carbon and nutrients and thus can be used as soil amendments; however, it is not fully explored how the biochar amended fishpond sediments can affect soil properties/fertility and modulate plant physiological and biochemical changes, particularly under contamination stress. Therefore, a comprehensive investigation was carried out to explore the effects of FPS and BC-treated FPS (BFPS) on soil and on spinach (Spinacia oleracea L.) grown in chromium (Cr) contaminated soils. Addition of FPS and BFPS to soil caused an increase in nutrients content and reduced Cr levels in soil, which consequently resulted in a significant increase in plant biomass, chlorophyll pigments, and photosynthesis, over the control treatment. The most beneficial effect was observed with the BFPS applied at 35 %, which further increased the antioxidant enzymes (by 2.75-fold, at minimum), soluble sugars by 24.9 %, and upregulated the gene expression activities. However, the same treatment significantly decreased proline content by 74.9 %, Malondialdehyde by 65.6 %, H₂O₂ by 65.1 %, and Cr concentration in spinach root and shoot tissues. Moreover, the average daily intake analysis showed that BFPS (at 35 %) could effectively reduce human health risks associated with Cr consumption of leafy vegetables. In conclusion, these findings are necessary to provide guidelines for the reutilization of aquaculture sediments as an organic fertilizer and a soil amendment for polluted soils. However, more future field studies are necessary to provide guidelines and codes on aquaculture sediments reutilization as organic fertilizer and soil amendment for polluted soils, aiming for a more sustainable food system in China and globally, with extended benefits to the ecosystem and human.

Influence of arbuscular mycorrhizal fungi on mercury accumulation in rice (Oryza sativa L.): From enriched isotope tracing perspective

The microorganisms that co-exist between soil and rice systems in heavy metal-contaminated soil environments play important roles in the heavy metal pollution states of rice, as well as in the growth of the rice itself. In this study, in order to further examine the effects of soil microorganisms on the mercury (Hg) uptake of rice plants and determine potential soil phytoremediation agents, an enriched ¹⁹⁹Hg isotope was spiked in a series of pot experiments to trace the absorption and migration of Hg and rice growth in the presence of arbuscular mycorrhizal fungi (AMF). It was observed that the AMF inoculations significantly reduced the Hg concentration in the rice. The Hg concentration in rice in the AMF inoculation group was between 52.82% and 96.42% lower than that in the AMF non-inoculation group. It was also interesting to note that the presence of AMF tended to cause Hg (especially methyl-Hg (Me¹⁹⁹Hg)) to migrate and accumulate in the non-edible parts of the rice, such as the stems and leaves. Under the experimental conditions selected in this study, the proportion of Me¹⁹⁹Hg in rice grains decreased from 9.91% to 27.88%. For example, when the exogenous Hg concentration was 0.1 mg/kg, the accumulated methyl-Hg content in the grains of the rice in the AMF inoculation group accounted for only 20.19% of the Me¹⁹⁹Hg content in the rice plants, which was significantly lower than that observed in the AMF non-inoculated group (48.07%). AMF also inhibited the absorption of Hg by rice plants, and the decrease in the Hg concentration levels in rice resulted in significant improvements in growth indices, including biomass and micro-indexes, such as antioxidant enzyme activities. The improvements occurred mainly because the AMF formed symbiotic structures with the roots of rice plants, which fixed Hg in the soil. AMF also reduce the bioavailability of Hg by secreting a series of substances and changing the physicochemical properties of the rhizosphere soil. These findings suggest the possibility of using typical co-existing microorganisms for the remediation of soil heavy metal contamination and provide valuable insights into reducing human Hg exposure through rice consumption.

Recent progresses, challenges, and opportunities of carbon-based materials applied in heavy metal polluted soil remediation

The application of carbon-based materials (CBMs) for heavy metal polluted soil remediation has gained growing interest due to their versatile properties and excellent remediation performance. Although the progresses on applications of CBMs in removing heavy metal from aqueous solution and their corresponding mechanisms were well known, comprehensive review on applications of CBMs in heavy metal polluted soil remediation were less identified. Therefore, this review provided insights into advanced progresses on utilization of typical CBMs including biochar, activated carbon, graphene, graphene oxide, carbon nanotubes, and carbon black for heavy metal polluted soil remediation. The mechanisms of CBM remediation of heavy metals in soil were summarized, mainly including physical adsorption, precipitation, complexation, electrostatic interaction, and cationic-π coordination. The key factors affecting the remediation effect include soil pH, organic matter, minerals, microorganisms, coexisting ions, moisture, and material size. Disadvantages of CBMs were also included, such as: potential health risks, high cost, and difficulty in achieving co-passivation of anions and cations. This work will contribute to our understanding of current research advances, challenges, and opportunities for CBMs remediation of heavy metal-contaminated soils.

Impact of physiochemical properties, microbes and biochar on bioavailability of toxic elements in the soil: a review

The pollution of toxic elements (TEs) in the ecosystem exhibits detrimental effects on the human health. In this paper, we debated remediation approaches for TEs polluted soils via immobilization methods employing numerous amendments with reverence to type of soil and metals, and amendment, immobilization competence, fundamental processes and field applicability. We argued the influence of pH, soil organic matter, textural properties, microbes, speciation and biochar on the bioavailability of TEs. All these properties of soil, microbes and biochar are imperative for effective and safe application of these methods in remediation of TEs contamination in the ecosystem. Further, the application of physiochemical properties, microbes and biochar as amendments has significant synergistic impacts not only on absorption of elements but also on diminution of toxic elements.

Role of biochar and compost in cadmium immobilization and on the growth of Spinacia oleracea

This research was carried out to evaluate the effect of biochar and compost application on Spinacia oleracea growth in cadmium contaminated soil. Cd toxicity decreased plant growth and biomass significantly and also negatively affected the physiological and biochemical attributes of plants. However, the application of biochar and compost improved the contaminated soil by reducing Cd toxicity and causing its immobilization, which in turn improved plant growth. The combined application of biochar and compost significantly (p < 0.05) enhanced biomass and photosynthetic pigments development in plants. The treatments also increased membrane stability index by 45.12% and enhanced water using efficiency by 218.22%, respectively. The increase in antioxidant activities was 76.03%, 29.02%, and 123.27% in superoxide dismutase, peroxidase, and catalase, respectively. The combined application also reduced the cadmium content (reduced 40.14% in root and 51.16% shoot), its translocation (19.67% decrease), and bioaccumulation (52.63% and 40.32% decrease in Cd content in shoot and root, respectively) in spinach plant. Among the two selected varieties of S. oleracea, Desi palak (V1) performed better as compared to Kanta palak (V2). It can be concluded that the combined application of biochar and compost is one of the best strategies to reduce the toxicity level of Cd in plants and to improve their growth.

Nickel Toxicity Interferes with NO3−/NH4+ Uptake and Nitrogen Metabolic Enzyme Activity in Rice (Oryza sativa L.)

The excessive use of nickel (Ni) in manufacturing and various industries has made Ni a serious pollutant in the past few decades. As a micronutrient, Ni is crucial for plant growth at low concentrations, but at higher concentrations, it can hamper growth. We evaluated the effects of Ni concentrations on nitrate (NO₃⁻) and ammonium (NH₄⁺) concentrations, and nitrogen metabolism enzyme activity in rice seedlings grown in hydroponic systems, using different Ni concentrations. A Ni concentration of 200 μM significantly decreased the NO₃⁻ concentration in rice leaves, as well as the activities of nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), and glutamate synthetase (GOGAT), respectively, when compared to the control. By contrast, the NH₄⁺ concentration and glutamate dehydrogenase (GDH) activity both increased markedly by 48% and 46%, respectively, compared with the control. Furthermore, the activity of most active aminotransferases, including glutamic pyruvic transaminase (GPT) and glutamic oxaloacetic transaminase (GOT), was inhibited by 48% and 36%, respectively, in comparison with the control. The results indicate that Ni toxicity causes the enzymes involved in N assimilation to desynchronize, ultimately negatively impacting the overall plant growth.

Biochar enhances wheat crop productivity by mitigating the effects of drought: Insights into physiological and antioxidant defense mechanisms

Drought stress is a major limitation in wheat production around the globe. Organic amendments could be the possible option in semi-arid climatic conditions to mitigate the adverse effects of drought at critical growth stages. Wheat straw biochar (BC₀ = Control, BC₁ = 3% biochar and BC₂ = 5% biochar) was used to alleviate the drought stress at tillering (DTS), flowering (DFS), and grain filling (DGFS) stages. Drought stress significantly reduced the growth and yield of wheat at critical growth stages, with DGFS being the most susceptible stage, resulting in significant yield loss. Biochar application substantially reduced the detrimental effects of drought by improving plant height (15.74%), fertile tiller count (17.14%), spike length (16.61%), grains per spike (13.89%), thousand grain weight (10.4%), and biological yield (13.1%) when compared with the control treatment. Furthermore, physiological parameters such as water use efficiency (38.41%), stomatal conductance (42.76%), chlorophyll a (19.3%), chlorophyll b (22.24%), transpiration rate (39.17%), photosynthetic rate (24.86%), electrolyte leakage (-42.5%) hydrogen peroxide (-18.03%) superoxide dismutase (24.66%), catalase (24.11%) and peroxidase (-13.14%) were also improved by biochar application. The use of principal component analysis linked disparate scales of our findings to explain the changes occurred in wheat growth and yield in response to biochar application under drought circumstances. In essence, using biochar at 5% rate could be a successful strategy to promote wheat grain production by reducing the hazardous impacts of drought stress.

Biochar Alleviates Phytotoxicity by Minimizing Bioavailability and Oxidative Stress in Foxtail Millet (Setaria italica L.) Cultivated in Cd- and Zn-Contaminated Soil

Soil contamination with multiple heavy metals is a global environmental issue that poses a serious threat to public health and ecological safety. Biochar passivation is an efficient and economical technology to prevent heavy metal contamination of Cd; however, its effects on compound-contaminated and weakly alkaline soil remain unclear. Further, the mechanisms mediating the immobilization effects of biochar have not been evaluated. In this study, three biochar treated at different pyrolytic temperatures [300°C (BC300), 400°C (BC400), and 500°C (BC500)] were applied to Cd-/Zn-contaminated soils, and their effects on plant growth, photosynthetic characteristics, Cd/Zn accumulation and distribution in foxtail millet were evaluated. Further, the effect of biochar application on the soil physicochemical characteristics, as well as the diversity and composition of the soil microbiota were investigated. Biochar significantly alleviated the phytotoxicity of Cd and Zn. DTPA (diethylenetriamine pentaacetic acid)-Cd and DTPA-Zn content was significantly reduced following biochar treatment via the transformation of exchangeable components to stable forms. BC500 had a lower DTPA-Cd content than BC300 and BC400 by 42.87% and 39.29%, respectively. The BC500 passivation ratio of Cd was significantly higher than that of Zn. Biochar application also promoted the growth of foxtail millet, alleviated oxidative stress, and reduced heavy metal bioaccumulation in shoots, and transport of Cd from the roots to the shoots in the foxtail millet. The plant height, stem diameter, biomass, and photosynthetic rates of the foxtail millet were the highest in BC500, whereas the Cd and Zn content in each organ and malondialdehyde and hydrogen peroxide content in the leaves were the lowest. Moreover, biochar application significantly increased the abundance of soil bacteria and fungi, as well as increasing the fungal species richness compared to no-biochar treatment. Overall, biochar was an effective agent for the remediation of heavy metal-contaminated soil. The passivation effect of biochar exerted on heavy metals in soil was affected by the biochar pyrolysis temperature, with BC500 showing the best passivation effect.

Phytoremediator Potential of Ipomea asarifolia in Gold Mine Waste Treated with Iron Impregnated Biochar

Growing environmental pollution in recent decades has been generating potentially toxic elements (PTE) which pose an ongoing threat to terrestrial and aquatic ecosystems and human health, especially in mining areas. Biochar and PTE-tolerant species have been used in soil remediation as they are environmentally friendly alternatives. This study aimed to assess the influence of açaí seed biochar (Euterpe oleracea Mart), impregnated with iron (BFe) or not (BC), on the bioavailability of PTEs, in a multi-contaminated soil from a gold (Au) mining area in the Amazon, using Ipomea asarifolia as a plant test since it was naturally growing on the tailings. BC increased the soil pH while BFe reduced. Biochars increased PTEs in the oxidizable fraction (linked to soil organic matter). The use of BC and BFe improved the immobilization of PTEs and BC increased arsenic (As) in the easily soluble fraction in the soil. Moreover, plants grown with biochars showed lower dry matter yield, higher concentrations of PTEs and lower nutrient content than the control treatment. According to the phytoextraction and translocation factors, Ipomea asarifolia can be classified as a species with potential for phytostabilization of Zn and tolerant to other PTEs, mainly As.

Potential of organic and inorganic amendments for stabilizing nickel in acidic soil, and improving the nutritional quality of spinach

Contamination of soils by nickel (Ni) has become a serious environmental problem throughout the world, and this substance wields dangerous effects on the ecosystem and food chain. A pot experiment was conducted to examine the effect of rice straw (RS), rice straw biochar (BI), and calcite (CC) at 1% and 2% application rates in a Ni-contaminated soil. The objective was to potentially stabilize Ni and reduce its bioavailability to spinach (Spinacia Oleracea L.). Spinach plants were grown in a Ni-contaminated Ultisol (commonly known as a red clay soil). Plant growth parameter results indicated that a BI 2% application rate significantly increased the root and shoots dry biomass increased by 1.7- and 6.3-fold, respectively, while essential nutrients were enhanced in the spinach plant compared to those in the untreated soil (CK). Moreover, adding amendments significantly decreased CaCl₂ extractable Ni by 62.5% 94.1%, and 87.2%, while the toxicity characteristics leaching procedure (TCLP) fell by 26.7%, 47.8%, and 41.7% when using RS, BI, and CC, respectively, at 2% compared to CK. The Ni concentrations in the spinach roots declined by 51.6%, 73.3%, and 68.9%, and in the shoots reduced by 54.1%, 76.7%, and 70.8% for RS, BI, and CC, at a 2% application rate, respectively. Bio-concentration factor (BCF) and translocation factor (TF) dropped significantly by as much as 72.7% and 20%, respectively, for BI 2% application rate. Results of the present study clearly indicated that biochar potential soil amendments for Ni stabilization, thereby reducing its bioavailability in the Ni-contaminated soil. This process enhanced the safety of food to be consumed and mitigated security risks.

Potential Effects of Biochar Application for Improving Wheat (Triticum aestivum L.) Growth and Soil Biochemical Properties under Drought Stress Conditions

Different soil amendments are applied to improve soil properties and to achieve higher crop yield under drought conditions. The objective of the study was to investigate the role of biochar for the improvement of wheat (Triticum aestivum L.) growth and soil biochemical properties under drought conditions. A pot experiment with a completely randomized design was arranged with four replications in a wire house. Drought was imposed on two critical growth stages (tillering and grain filling) and biochar was applied to the soil 10 days before sowing at two different rates (28 g kg−1 and 38 g kg−1). Soil samples were collected to determine the soil properties including soil respiration and enzymatic parameters after crop harvesting. Results showed that water stress negatively affects all biochemical properties of the soil, while biochar amendments positively improved these properties. Application of biochar at 38 g kg−1 provided significantly higher mineral nutrients, Bray P (18.72%), exchangeable-K (7.44%), soil carbon (11.86%), nitrogen mineralization (16.35%), and soil respiration (6.37%) as a result of increased microbial activities in comparison with the 28 g kg−1 rate.

Electrospun Polyacrylonitrile/Lignin/Poly(Ethylene Glycol)-Based Porous Activated Carbon Nanofiber for Removal of Nickel(II) Ion from Aqueous Solution

The issue of heavy metal contamination has caused a great deal of concern among water quality experts today, as it contributes to water pollution. Activated carbon nanofibers (ACNFs) showed a significant ability in removing heavy metals from the wastewater. In this study, polyacrylonitrile (PAN) was blended and electrospun with an abundant and inexpensive biopolymer, lignin and a water soluble polymer, poly(ethylene glycol) (PEG), by using an electrospinning technique to form nanofibers. The electrospun nanofibers were then investigated as a precursor for the production of porous ACNFs to study the removal of nickel(II) ions by adsorption technique. PEG was added to act as a porogen and to create the porous structure of carbon nanofibers (CNFs). CNFs were prepared by thermal treatment of the electrospun nanofibers and followed by activation of CNFs by thermal and acid treatment on CNFs. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) spectral analysis of the ACNFs showed a strong absorption peak of the C-O functional group, indicating the increase in the oxygenated compound. Field emission scanning electron microscopy (FESEM) images concluded that the ACNFs have more porous and compact fibers with a smaller fiber diameter of 263 ± 11 nm, while the CNFs are less compact and have slightly larger fiber diameter of 323 ± 6 nm. The adsorption study showed that the ACNFs possessed a much higher adsorption capacity of 18.09 mg/g compared with the CNFs, which the amount adsorbed was achieved only at 2.7 mg/g. The optimum adsorption conditions that gave the highest percentage of 60% for nickel(II) ions removal were 50 mg of adsorbent dosage, 100 ppm of nickel(II) solution, pH 3, and a contact time of 60 min. The study demonstrated that the fabrication of ACNFs from PAN/lignin/PEG electrospun nanofibers have potential as adsorbents for the removal of heavy metal contaminants.

Nickel in soil and water: Sources, biogeochemistry, and remediation using biochar

Nickel (Ni) is a potentially toxic element that contaminates soil and water, threatens food and water security, and hinders sustainable development globally. Biochar has emerged as a promising novel material for remediating Ni-contaminated environments. However, the potential for pristine and functionalized biochars to immobilize/adsorb Ni in soil and water, and the mechanisms involved have not been systematically reviewed. Here, we critically review the different dimensions of Ni contamination and remediation in soil and water, including its occurrence and biogeochemical behavior under different environmental conditions and ecotoxicological hazards, and its remediation using biochar. Biochar is effective in immobilizing Ni in soil and water via ion exchange, electrostatic attraction, surface complexation, (co)precipitation, physical adsorption, and reduction due to the biogeochemistry of Ni and the interaction of Ni with surface functional groups and organic/inorganic compounds contained in biochar. The efficiency for Ni removal is consistently greater with functionalized than pristine biochars. Physical (e.g., ball milling) and chemical (e.g., alkali/acidic treatment) activation achieve higher surface area, porosity, and active surface groups on biochar that enhance Ni immobilization. This review highlights possible risks and challenges of biochar application in Ni remediation, suggests future research directions, and discusses implications for environmental agencies and decision-makers.

Heavy metals immobilization and improvement in maize (Zea mays L.) growth amended with biochar and compost

Soil with heavy metals contamination, mainly lead (Pb), cadmium (Cd), and chromium (Cr) is a progressively worldwide alarming environmental problem. Recently, biochar has been used as a soil amendment to remediate contaminated soils, but little work has been done to compare with other organic amendments like compost. We investigated biochar and compost's comparative effect on Pb, Cd, and Cr immobilization in soil, photosynthesis, and growth of maize plants. Ten kg soil was placed in pots and were spiked with Pb, Cd, and Cr at concentrations 20, 10, 20 mg kg^-1. The biochar and compost treatments included 0, 0.5, 1, 2, and 4% were separately applied to the soil. The crop from pots was harvested after 60 days. The results show that the highest reduction of AB-DTPA extractable Pb, Cd, and Cr in soil was 79%, 61% and 78% with 4% biochar, followed by 61%, 43% and 60% with 4% compost compared to the control, respectively. Similarly, the highest reduction in shoot Pb, Cd, and Cr concentration was 71%, 63% and 78%with 4% biochar, followed by 50%, 50% and 71% with 4% compost than the control, respectively. The maximum increase in shoot and dry root weight, total chlorophyll contents, and gas exchange characteristics were recorded with 4% biochar, followed by 4% compost than the control. The maximum increase in soil organic matter and total nitrogen (N) was recorded at 4% biochar application while available phosphorus and potassium in the soil at 4% compost application. It is concluded that both biochar and compost decreased heavy metals availability in the soil, reducing toxicity in the plant. However, biochar was most effective in reducing heavy metals content in soil and plant compared to compost. In the future, more low-cost, eco-friendly soil remediation methods should be developed for better soil health and plant productivity.

Effects of nanoparticles on trace element uptake and toxicity in plants: A review

Agricultural soils are receiving higher inputs of trace elements (TEs) from anthropogenic activities. Application of nanoparticles (NPs) in agriculture as nano-pesticides and nano-fertilizers has gained rapid momentum worldwide. The NPs-based fertilizers can facilitate controlled-release of nutrients which may be absorbed by plants more efficiently than conventional fertilizers. Due to their large surface area with high sorption capacity, NPs can be used to reduce excess TEs uptake by plants. The present review summarizes the effects of NPs on plant growth, photosynthesis, mineral nutrients uptake and TEs concentrations. It also highlights the possible mechanisms underlying NPs-mediated reduction of TEs toxicity at the soil and plant interphase. Nanoparticles are effective in immobilization of TEs in soil through alteration of their speciation and improving soil physical, chemical, and biological properties. At the plant level, NPs reduce TEs translocation from roots to shoots by promoting structural alterations, modifying gene expression, and improving antioxidant defense systems. However, the mechanisms underlying NPs-mediated TEs uptake and toxicity reduction vary with NPs type, mode of application, time of NPs exposure, and plant conditions (e.g., species, cultivars, and growth rate). The review emphasizes that NPs may provide new perspectives to resolve the problem of TEs toxicity in crop plants which may also reduce the food security risks. However, the potential of NPs in metal-contaminated soils is only just starting to be realized, and additional studies are required to explore the mechanisms of NPs-mediated TEs immobilization in soil and uptake by plants. Such future knowledge gap has been highlighted and discussed.

Organic and inorganic amendments for the remediation of nickel contaminated soil and its improvement on Brassica napus growth and oxidative defense

In-situ stabilization has been considered an effective way to remediate metal contaminated soil. Thus, pot experiments were undertaken to investigate the effectiveness of multiple stabilization agents such as biochar (BC), mussel shell (MS), zeolite (ZE) and limestone (LS) on the immobilization of Ni, physicochemical features and enzyme activities in polluted soil. Results showed that the sole application of Ni adversely affected the rapeseed growth, photosynthetic pigments, and antioxidative defense. However, the addition of amendments to the contaminated soil significantly reduced Ni bioavailability. The XRD analysis confirmed the formation of Ni related ligands and FTIR showed the presence of hydroxyl, carboxyl and sulfur functional groups, as well as complexation and adsorption of Ni on amendments. Among multiple amendments, biochar significantly enhanced plant biomass attributes and total chlorophyll content. Moreover, addition of amendments also strengthened the antioxidant defense by decreasing Ni induced oxidative stress (H₂O₂ and O₂^.-), increased macronutrient availability, reduced Ni uptake and improved soil health. The qPCR analysis showed that the Ni transporters were significantly suppressed by amendments, which is correlated with the lower accumulation of Ni in rapeseed. The present study showed that immobilizing agents, especially biochar, is an effective amendment to immobilize Ni in soil, which restricts its entry into the food chain.

Combined effects of biochar and chicken manure on maize (Zea mays L.) growth, lead uptake and soil enzyme activities under lead stress

The goal of the present work was to evaluate the additive effects of biochar and chicken manure on maize growth in Pb-contaminated soils. In this study, we conducted a pot experiment to investigate how biochar in soil (20, 40 g·kg^-1), chicken manure in soil (20, 40 g·kg^-1), or a combination of biochar and chicken manure in soil (each at 20 g·kg^-1) effect maize growth, Pb uptake, leaves' antioxidant enzymatic activities, and soil enzyme activities under artificial conditions to simulate moderate soil pollution (800 Pb mg·kg^-1). The results showed that all biochar and/or chicken manure treatments significantly (P < 0.05) increased maize plant height, biomass, and superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activity but decreased the malondialdehyde (MDA) content. These results indicated that amending the soil with biochar and/or chicken manure could alleviate Pb's phytotoxicity. The biochar and/or chicken manure treatments remarkably decreased the Pb concentration in maize roots, stems, leaves, bioconcentration factor (BCF), translocation factor (TF), and available Pb concentration in the soil. Amending the soil with chicken manure alone was more effective at increasing maize growth and antioxidant enzymatic activity; the biochar treatment alone was more effective at inducing soil alkalinization and contributing to Pb immobilization. The combined use of biochar and chicken manure had an additive effect and produced the largest increases in maize growth, leaves' antioxidant enzymatic activity, and soil enzyme activity. Their combined use also led to the most significant decreases in maize tissues Pb and soil available Pb. These results suggest that a combination of biochar and chicken manure was more effective at reducing soil Pb bioavailability and uptake by maize tissues, and increasing maize growth. This combination increased plant height by 43.23% and dry weight by 69.63% compared to the control.

Photosynthesis, Chlorophyll Fluorescence, and Yield of Peanut in Response to Biochar Application

The effect of biochar application on photosynthetic traits and yield in peanut (Arachis hypogaea L.) is not well understood. A 2-year field experiment was conducted in Northwest Liaoning, China to evaluate the effect of biochar application [0, 10, 20, and 40 t ha^-1 (B0, B10, B20, and B40)] on leaf gas exchange parameters, chlorophyll fluorescence parameters, and yield of peanut. B10 improved photochemical quenching at flowering and pod set and reduced non-photochemical quenching at pod set, relative to B0. B10 and B20 increased actual photochemical efficiency and decreased regulated energy dissipated at pod set, relative to B0. B10 significantly increased net photosynthetic rate, transpiration rate, stomatal conductance, and water use efficiency at flowering and pod set, relative to B0. Compared with B0, B10 significantly improved peanut yield (14.6 and 13.7%) and kernel yield (20.2 and 14.4%). Biochar application increased leaf nitrogen content. B10 and B20 significantly increased plant nitrogen accumulation, as compared to B0. The net photosynthetic rate of peanut leaves had a linear correlation with plant nitrogen accumulation and peanut yield. The application of 10 t ha^-1 biochar produced the highest peanut yield by enhancing leaf photosynthetic capacity, and is thus a promising strategy for peanut production in Northwest Liaoning, China.

Biological effects of biochar and zeolite used for remediation of soil contaminated with toxic heavy metals

Biochar and zeolite are widely used in the remediation of soil contaminated with toxic heavy metals. However, the interaction of these amendments and their effects on grass productivity have not been comprehensively summarized. The aim of this study was to investigate the biological effects of zeolite and biochar used as soil amendments in the process of remediating soil contaminated with Cd, Pb and Zn. In a pot experiment, the following treatments were applied: zeolite, biochars produced at temperatures of 350 °C and 550 °C, mixtures of biochars and zeolite, and a control treatment without any amendments. The soil amendments were tested on two grass species: tall fescue (Festuca arundinacea Schreb.) and cocksfoot (Dactylis glomerata L.). The root morphometric parameters and aboveground production were determined in 2017 and 2018.Higher biomass production was observed in the tested grasses in the treatments with zeolite alone (0.229 kg DM m^-2) or mixed with the biochars (0.239 kg DM m^-2) than in control treatment (0.029 kg DM m^-2). Zeolite used in contaminated soil significantly affected root biomass and root morphology parameters. Zeolite application resulted in significantly higher root biomass (2.30 mg cm^-3) and root length (76.61 cm cm^-3) than those in the treatments without zeolite (0.29 mg cm^-3 and 6.90 cm cm^-3). Biochar as a soil amendment did not affect most root morphometric parameters. The application of biochars only slightly reduced the root diameter of cocksfoot. The root diameter of tall fescue was similar in all treatments (0.075 mm) except the control (0.063 mm) and biochar 550 treatments (0.067 mm), in which slightly thinner roots were observed.

Immobilization and mitigation of chromium toxicity in aqueous solutions and tannery waste-contaminated soil using biochar and polymer-modified biochar

This study was conducted to investigate the potential of Jujube (Ziziphus jujube L) wood waste-derived biochar (BC) and its derivative polymer-modified biochar (PBC) in removing hexavalent chromium (Cr^VI) from aqueous solutions and in achieving Cr stabilization in tannery waste-contaminated soil. BC was produced at three different pyrolysis temperature (300 °C, 500 °C, 700 °C) and was polymerized with acrylamide and N, N1 methylenebisacrylamide. The results showed that Cr^VI adsorption is a function of the pH and Cr^VI initial concentration of the solution. The PBC showed highest sorption efficiency for Cr^VI removal, which amounted to 76.4%-99.6% of the Cr^VI overall initial concentrations (5-40 mg L^-1) at an initial pH of 2. In greenhouse, wheat (Triticum aestivum L) was cultivated as a test crop in pots with tannery waste-contaminated soil along with BCs and PBCs amendments. The BC and PBC amended soil showed 47.7% and 65% less Cr uptake by the plant roots in comparison with unamended soil, respectively. In addition, zero concentration of Cr in the plant shoots was noted with the PBC-amended soil, while the Cr concentration in the shoots was decreased by 89% with the BC-amended soil. Thus, it was concluded that BC and PBC have great potential in removing Cr^VI from aqueous phases and in decreasing the Cr mobility and bioavailability in soil.

Comparison of plant growth and remediation potential of pyrochar and thermal desorption for crude oil-contaminated soils

Crude oil contamination is a serious environmental threat for soil and plants growing in it. This study provides the first experimental evidence for comparison of the efficacy of pyrochar (slow pyrolysis biochar), thermal desorption and their combined application for degradation of crude oil contaminated soil (0%, 10%, and 20%), and growth of lettuce under glasshouse conditions. Pyrochar was produced by pyrolysis of sawdust at 350 °C, whereas thermal desorption was done by soil pyrolysis at 500 °C. Soil incubations were done for 120 days. The results of soil analysis showed that the crude oil degradation efficiency for the combined application was highest (40%), whereas pyrochar and thermal desorption was 25% and 19.6%, respectively. The maximum degradation products of crude oil were manifested by the detection of low molecular weight hydrocarbons (ranged between 173 and 422) in the soil with combined application treatment using Gas Chromatography-Mass Spectrometry (GC–MS) analysis. Crude oil contamination significantly reduced the germination and growth of the lettuce plants. Similarly, the combined application also improved plant growth by an increase of 24% in germination percentage, 35.5% in seedling vigor index, and 27% in promptness index under 20% crude oil contamination. Remediation caused a significant increase in fresh and dry biomass (40%), leaf area (30%), total chlorophyll (21%), water potential (23.6%), osmotic potential (27%), and membrane stability index (40%). Moreover, there was an increase in the contents of proline (32%), total amino acids (29%), soluble sugars (37%), proteins (27%), and antioxidant enzymes such as superoxide dismutase (19%), catalase (33%) and peroxidase (38%). This study confirmed the efficacy of pyrochar (slow pyrolysis biochar), thermal desorption, and their combined application for crude oil decontamination of soil at laboratory scale and also in improving soil usability by improved germination and growth of lettuce.

Mapping leaf metal content over industrial brownfields using airborne hyperspectral imaging and optimized vegetation indices

Monitoring plant metal uptake is essential for assessing the ecological risks of contaminated sites. While traditional techniques used to achieve this are destructive, Visible Near-Infrared (VNIR) reflectance spectroscopy represents a good alternative to monitor pollution remotely. Based on previous work, this study proposes a methodology for mapping the content of several metals in leaves (Cr, Cu, Ni and Zn) under realistic field conditions and from airborne imaging. For this purpose, the reflectance of Rubus fruticosus L., a pioneer species of industrial brownfields, was linked to leaf metal contents using optimized normalized vegetation indices. High correlations were found between the vegetation indices exploiting pigment-related wavelengths and leaf metal contents (r ≤ - 0.76 for Cr, Cu and Ni, and r ≥ 0.87 for Zn). This allowed predicting the metal contents with good accuracy in the field and on the image, especially Cu and Zn (r ≥ 0.84 and RPD ≥ 2.06). The same indices were applied over the entire study site to map the metal contents at very high spatial resolution. This study demonstrates the potential of remote sensing for assessing metal uptake by plants, opening perspectives of application in risk assessment and phytoextraction monitoring in the context of trace metal pollution.

Brassinosteroid and hydrogen peroxide improve photosynthetic machinery, stomatal movement, root morphology and cell viability and reduce Cu- triggered oxidative burst in tomato

Brassinosteroids and hydrogen peroxide (H₂O₂) are extensively used to combat several environmental factors, including heavy metal stress in plants, but their cumulative impact on the maintenance of copper (Cu) homeostasis in plants could not be dissected at elevated level. This study was executed to explore the roles of 24-epibrassinolide (EBL; foliar) and H₂O₂ (root dipping) in resilience of tomato (Solanum lycopersicum L.) plants to Cu stress. The cumulative effect of EBL and H₂O₂ in tomato plants grown under Cu stress (10 or 100 mg kg^-1 soil) were assessed. Roots of 20 d old plants were submerged in 0.1 mM of H₂O₂ solution for 4 h and subsequently transplanted in the soil-filled earthen pots and at 30 day after transplantation (DAT), the plants were sprinkled with deionized water (control), and/or 10^-8 M EBL and plant performances were evaluated at 40 DAT. High Cu (100 mg kg^-1 soil) concentration considerably reduced photosynthetic efficacy, cell viability, and plant growth, and deformed chloroplast ultrastructure and root morphology with altered stomatal behavior, but boosted the activity of antioxidant enzymes, proline content and electrolyte leakage in the leaves of tomato. Moreover, EBL and H₂O₂ implemented through distinct modes improved photosynthetic efficiency, modified chloroplast ultrastructure, stomatal behavior, root structure, cell viability and production of antioxidants and proline (osmolyte) that augmented resilience of tomato plants to Cu stress. This study revealed the potential of EBL and H₂O₂ applied through distinct mode could serve as an effective strategy to reduce Cu-toxicity in tomato crop.

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.

The effects of non-stabilised and Na-carboxymethylcellulose-stabilised iron oxide nanoparticles on remediation of Co-contaminated soils

A pot experiment was carried out to evaluate the efficiency of six types of non-stabilised and Na-carboxymethylcellulose (CMC)-stabilised iron oxide nanoparticles (α-FeOOH, α-Fe₂O₃, and Fe₃O₄) on the immobilisation of cobalt (Co) in a soil spiked with different concentrations of it (5, 25, 65, 125, 185 mg kg^-1). Amendments were added to soil samples at the rate of 0.5%, and the samples incubated for 60-days. The addition of amendments significantly decreased the concentrations of DTPA-Co and MgCl₂-Co, compared with the unamended control. The highest decrease in concentration of DTPA-Co and MgCl₂-Co was obtained by the application of CMC-stabilised Fe₃O₄ (MC) when the concentration of soil total Co was low (5 and 25 mg kg^-1) and by the use of CMC-stabilised α-FeOOH (GC) when the concentration of soil total Co was high (65, 125, and 185 mg kg^-1), as compared to the control. CMC-stabilised iron oxide nanoparticles were more effective than non-stabilised nanoparticles in the immobilisation of Co. To investigate the effectiveness of iron oxide amendments on the chemical species of Co in the soil spiked with 65 mg kg^-1 of this metal, sequential extraction was performed. The concentration of EXCH (exchangeable) and CARB (carbonate) bound fractions decreased significantly after treatment by different amendments. In particular, GC reduced the concentration of EXCH and CARB bound fractions by 20.87, and 17.52%, respectively, compared with the control. Also amendments significantly increased the concentration of FeMn-OX (Fe-Mn oxides), and OM (organic matter) bound, and RES (residual) fractions.

Cadmium Immobilization in the Rhizosphere and Plant Cellular Detoxification: Role of Plant-Growth-Promoting Rhizobacteria as a Sustainable Solution

Food is the major cadmium (Cd)-exposure pathway from agricultural soils to humans and other living entities and must be reduced in an effective way. A plant can select beneficial microbes, like plant-growth-promoting rhizobacteria (PGPR), depending upon the nature of root exudates in the rhizosphere, for its own benefits, such as plant growth promotion as well as protection from metal toxicity. This review intends to seek out information on the rhizo-immobilization of Cd in polluted soils using the PGPR along with plant nutrient fertilizers. This review suggests that the rhizo-immobilization of Cd by a combination of PGPR and nanohybrid-based plant nutrient fertilizers would be a potential and sustainable technology for phytoavailable Cd immobilization in the rhizosphere and plant cellular detoxification, by keeping the plant nutrition flow and green dynamics of plant nutrition and boosting the plant growth and development under Cd stress.

The Effects of Fertilizer Type and Application Time on Soil Properties, Plant Traits, Yield and Quality of Tomato

Compost is considered to be superior fertilizer for soil quality and productivity, and is commonly used with chemical fertilizer. The optimal mixed ratio of compost with chemical fertilizer and the best application time is necessary to know for sustainable agriculture practices and management. Compared to the control treatment, this study comprehensively evaluated the effects of four mixed ratios of compost with chemical fertilizer, two nitrogen application times of chemical fertilizer, and their interaction on the soil properties, plant traits, yield, and quality of tomato plants. The soil properties, plant traits, and yield of tomato with all compost-mixed fertilizers performed better than the treatment without fertilizer. Furthermore, the amounts of available nitrogen, phosphorus, organic matter, plant weight, and yield in a 30% chemical fertilizer + 70% compost treatments (CF30) were even better than those with pure chemical fertilizer (CF100). No significant effect of nitrogen application time and its interaction with the mixed ratio treatment was detected, and the quality of fruit remained consistent among treatments. This study demonstrated a suitable practical application method for cow manure compost as a nutrient source in tomato crop production under silty loam soil.

Compost and mycorrhizae application as a technique to alleviate Cd and Zn stress in Medicago sativa

Soil pollution by heavy metals, in the last decades, has become a worldwide major concern for which finding a solution is becoming more important to conserve soil for future generations. This study used an ecotoxicology approach to evaluate the effectiveness of compost and arbuscular mycorrhizal fungus (AMF) and their combination on Medicago sativa performance grown under Zn and Cd stress. At 600 mg/kg of Cd and Zn, a reduction of mycorrhization frequency by 3.6- and 2-fold, respectively, was observed without applying compost. The effect of AMF-Compost combination on alfalfa biomass production was enhanced in the absence and the presence of heavy metals. An improvement of relative water content by 1.7- and 1.5-fold was recorded in case AMF-Compost plant treatments grown under 600 mg/kg of Cd and Zn, respectively. The application of AMF-compost enhanced the stomatal conductance and total chlorophyll in alfalfa plants. Sugar contents were significantly increased in mycorrhized and treated plants with compost compared to the control, regardless of the applied Cd or Zn dose. Phenol content was significantly increased in plants amended with compost alone and treated by Cd. Regarding Cd and Zn accumulation, AMF-compost combination reduced the content of heavy metals accumulated in M. sativa.

Growth, Survival and Biomass Production of Barley in a Polluted Mine Soil Amended with Biochar and Animal Manure

In the present study, sheep manure (0%, 10% and 20% w/w) and biochar derived from coniferous tree woods (0%, 2.5% and 5% w/w) were incorporated into a multi-MTE contaminated soil from a former iron mine site and incubated for 10 days. A seeds of barley were grown in the amended soil and different morphological traits were measured after 30 days. Results indicated that MTE stress reduced the shoot length, stem diameter, leaf area, number of leaves and dry biomass as compared to the control. Organic amendments application increased soil pH and was found to affect significantly almost all the measured parameters. Animal manure was found effective in improvement of the morphological characteristics of barley plants comparing to biochar amendments. Our results suggested that animal manure could be used for reducing the effect of MTE on the morphological proprieties of barley grown in a former iron mine soil.

Effect of composted organic amendments and zinc oxide nanoparticles on growth and cadmium accumulation by wheat; a life cycle study

Cadmium (Cd) availability in arable soils is a serious issue while little is known about the role of co-composted organic amendments and zinc oxide nanoparticles (ZnO-NPs) foliar spray on biomass and Cd accumulation in wheat grains. The current study investigated the soil application of organic amendment (composted biochar and farmyard manure) at a level of 0, 1, and 2% w/w and foliar spray of ZnO-NPs (0, 100, and 200 mg/L) on biomass, yield, and Cd in wheat grains cultivated in an aged Cd-contaminated agricultural soil. The results indicated that organic amendment increased the biomass, chlorophyll concentrations, yield, and activities of peroxidase and superoxide dismutase of wheat while decreased the electrolyte leakage and Cd concentrations in different parts of wheat such as shoots, roots, husks, and grains. This effect of organic amendment was further enhanced by the foliar spray of ZnO-NPs in a dose-additive manner. Cadmium concentration in grains was below threshold level (0.2 mg/kg DW) for cereals in combined application of 200 mg/L ZnO-NPs and 1% organic amendment as well as in higher treatment (2%) of organic amendment and NPs. Thus, combined use of organic materials and NPs might be a suitable way of reducing Cd and probably other toxic trace element concentrations in wheat and other cereals.

Potential of rice straw biochar, sulfur and ryegrass (Lolium perenne L.) in remediating soil contaminated with nickel through irrigation with untreated wastewater

Background

Untreated wastewater carries substantial amount of heavy metals and causes potential ecological risks to the environment, food quality, soil health and sustainable agriculture.

Methodology

In order to reduce the incidence of nickel (Ni²⁺) contamination in soils, two separate experiments (incubation and greenhouse) were conducted to investigate the potentials of rice straw biochar and elemental sulfur in remediating Ni²⁺ polluted soil due to the irrigation with wastewater. Five incubation periods (1, 7, 14, 28 and 56 days), three biochar doses (0, 10 and 20 g kg⁻¹ of soil) and two doses of sulfur (0 and 5 g kg⁻¹ of soil) were used in the incubation experiment then the Ni²⁺ was extracted from the soil and analyzed, while ryegrass seeds Lolium perenne L. (Poales: Poaceae) and the same doses of biochar and sulfur were used in the greenhouse experiment then the plants Ni²⁺-uptake was determined.

Results

The results of the incubation experiment revealed a dose-dependent reduction of DTPA-extractable Ni²⁺ in soils treated with biochar. Increasing the biochar dose from 0 g kg⁻¹ (control) to 10 or 20 g kg⁻¹ (treatments) decreased the DTPA-extractable Ni²⁺ from the soil by 24.6% and 39.4%, respectively. The application of sulfur increased the Ni²⁺-uptake by ryegrass plant which was used as hyper-accumulator of heavy metals in the green house experiment. However, the biochar decreased the Ni²⁺-uptake by the plant therefore it can be used as animal feed.

Conclusions

These results indicate that the biochar and sulfur could be applied separately to remediate the Ni²⁺-contaminated soils either through adsorbing the Ni²⁺ by biochar or increasing the Ni²⁺ availability by sulfur to be easily uptaken by the hyper-accumulator plant, and hence promote a sustainable agriculture.

Application of co-composted farm manure and biochar increased the wheat growth and decreased cadmium accumulation in plants under different water regimes

Toxic trace element pollution in the agricultural soils may negatively affect the plant growth. This study mainly focused on investigating the impact of co-composted biochar and farmyard manure (FYM) on wheat growth and cadmium (Cd) accumulation by plants. The different ratios of FYM and biochar were composted for two and half months and mixed in Cd-contaminated soil at a rate of 2% w/w of each treatment. After this, wheat seeds were sown in the soil at normal soil moisture (70% of soil water holding capacity (WHC)) level. After 50-day of sowing, both normal and drought stress (35% WHC) levels were applied and plants were harvested at 122 days after seed sowing. The results depicted that Cd and drought alone depressed the wheat growth, elevated the oxidative stress and Cd contents in wheat tissues. However, application of co-composted treatments increased the growth, yield, chlorophyll contents and minimized the oxidative stress in the leaves along with the reduction of Cd concentrations in wheat tissues mainly in grains. The amendments enhanced the post-harvest soil pH and minimized the soil bioavailable Cd. The increasing ratios of biochar in the compost were most effective in improving the growth and alleviating Cd toxicity and its concentration in grains. Overall, co-composted biochar and FYM might be suitable for reducing Cd in grains, but the field studies in different soils and plants are required to further explore the effects of these amendments before final recommendations.

Enhancing Cadmium Tolerance and Pea Plant Health through Enterobacter sp. MN17 Inoculation Together with Biochar and Gravel Sand

Contamination of soils with heavy metals, particularly cadmium (Cd), is an increasingly alarming environmental issue around the world. Application of organic and inorganic immobilizing amendments such as biochar and gravel sand in combination with metal-tolerant microbes has the potential to minimize the bioavailability of Cd to plants. The present study was designed to identify the possible additive effects of the application of Enterobacter sp. MN17 as well as biochar and gravel sand on the reduction of Cd stress in plants and improvement of growth and nutritional quality of pea (Pisum sativum) plants through the reduction of Cd uptake. Pea seeds were surface sterilized then non-inoculated seeds and seeds inoculated with Enterobacter sp. MN17 were planted in artificially Cd-polluted soil, amended with the immobilizing agents biochar and gravel sand. Application of biochar and gravel sand alone and in combination not only improved the growth and nutritional quality of pea plants by in situ immobilization but also reduced the uptake of Cd by plant roots and its transport to shoots. However, microbial inoculation further enhanced the overall plant health as well as alleviated the toxic effects of Cd on the pea plants. These soil treatments also improved rates of photosynthesis and transpiration. The combined use of biochar and gravel sand with bacterial inoculation resulted in an increase in plant height (47%), shoot dry weight (42%), root dry weight (57%), and 100 seeds weight (49%) as compared to control plants in Cd contaminated soil. Likewise, biochemical constituents of pea seeds (protein, fat, fiber, and ash) were significantly increased up to 41%, 74%, 32%, and 72%, respectively, with the combined use of these immobilizing agents and bacterium. Overall, this study demonstrated that the combined application of biochar and gravel sand, particularly in combination with Enterobacter sp. MN17, could be an efficient strategy for the remediation of Cd contaminated soil. It could support better growth and nutritional quality of pea plants.

Co-composts of sewage sludge, farm manure and rock phosphate can substitute phosphorus fertilizers in rice-wheat cropping system

In the present study, various co-composts of sewage sludge (SS), farm manure (FM) and rock phosphate (RP) were prepared and their influence on phosphorus (P) uptake, soil P restoration and growth of rice crop and residual effect on wheat crop were investigated. The treatments comprised of T₁ (control, no amendment), T₂ (452 kg Nitrophos ha^-1, T₃ (724 kg SS₅₀:FM₅₀ ha^-1), T₄ (594 kg SS₁₀₀:FM₀ ha^-1), T₅ (728 kg SS₂₅:FM₂₅:RP₅₀ ha^-1), T₆ (726 kg SS_5O:FM₂₅:RP₂₅ ha^-1), T₇ (508 kg SS₇₅:FM₀:RP₂₅ ha^-1), and T₈ (546 kg SS₅₀:FM₀:RP₅₀ ha^-1). The post-experimental soil samples were analyzed for pH, EC, OM, Olsen's P. The plant samples (grains and straw of both crops) were analyzed for concentrations of P, and heavy metals. The P adsorption by post-wheat composts-amended soil was tested through Langmuir, and Freundlich adsorption isotherms. The investigated parameters (biomass, grain and straw yield, plant height and P concentrations in plant parts) were significantly increased in all composts as compared to the control treatment. The P uptake by the plants was higher in compost treatments as compared to the control and NP that shows long-term residual effect of applied composts. The maximum grain yield (1.63 Mg ha^-1) was obtained in T₅ followed by T₆ (1.52 Mg ha^-1). The P concentration in rice grains were recorded in the trend as T₈ (2.55%) > T₆ (2.24%) > T₄ (1.92%) = T₃ (1.88%) > T₇ (1.62%). It is evident that the combined application of FM (25%) and RP (50%) enhanced the effect of SS (25%) in terms of P bioavailability and yield parameters and can be effectively used as P fertilizer.

Effect of rice straw, biochar and calcite on maize plant and Ni bio-availability in acidic Ni contaminated soil

Metals that contaminate soil is one of the major problems seriously affecting sustainable agriculture worldwide. Nickel (Ni) toxicity to agricultural crops is a global problem. Mobility of heavy metals present in contaminated soil can be reduced by the amendment of soil passivators, which will ultimately reduce the risk of them entering the food chain. A greenhouse pot experiment was conducted to investigate the effects of rice straw (RS), biochar derived from rice straw (BI) and calcium carbonate (calcite) on Ni mobility and its up take by maize (Zea maize L.) plant. Maize crop was grown in Ni spiked (100 mg kg^-1) soil with three application rates of passivators (equivalent to 0, 1and 2% of each RS, BI and calcite) applied separately to the soil. Results revealed that the post-harvest soil properties (pH, DOC and MBC), plant phenology (plant height, root length, total dry weight) and physiological characteristics were significantly enhanced with passivator application. Additionally, incorporating passivator into the soil reduced Ni mobility (DTPA) by 68%, 88.9% and 79.3%, and leachability (TCLP) by 72.4%, 76.7% and 66.7% for RS, BI and calcite, respectively at 2% application rate. The Ni concentration in the maize shoots reduced by 30%, 95.2% and 95% and in the roots by 56%, 66% and 63.8% with RS, BI and calcite at 2% application rate, respectively. These findings suggest that the application of 2% biochar (BI) is very promising in reducing Ni uptake, and can reduce toxicity to plants, decrease mobility and leachability in the soil.

Residual effects of frequently available organic amendments on cadmium bioavailability and accumulation in wheat

Wheat (Triticum aestivum L.) cultivation in cadmium (Cd) polluted soil is a core concern to food quality and food security all over the world. Cadmium toxicity is mainly associated with a Cd influx from contaminated soils to human via grain consumption. Organic amendments are widely used for Cd immobilization and enhancement in plant growth, but the residual effects of these amendments are mostly unknown. The present study addressed the long-term effects of organic amendments in contaminated soils by evaluating their residual effects on 3rd crop (wheat) in the sequence. Initially six organic amendments viz. rice husk biochar (RHB), wheat-straw biochar (WSB), cotton-stick biochar (CSB), poultry manure (PM), press mud (PrMd) and farm manure (FM) were applied once at a rate of 2% in Cd (50 mg kg^-1) contaminated soil with wheat-rice rotation. After the harvest of wheat and rice crops, wheat (Var. Galaxy) was again grown in the same pots. Results revealed that plants grown under Cd stress (without any amendment) contain more tissue (root, shoot and grain) and soil AB-DTPA extractable Cd. The soil amended with RHB has shown lowest AB-DTPA extractable Cd (69% lower than control). Similarly, RHB application has significantly reduced wheat root, shoot and grain Cd concentrations compared to control and other amendments. Results have confirmed the effectiveness of RHB residual contents as an active amendment for restriction of Cd in non-bioavailable pool of soil and better growth and yield of wheat.

Poplar Biochar as an Alternative Substrate for Curly Endive Cultivated in a Soilless System

Imminent necessity for eco-friendly and low-cost substitutes to peat is a defiance in the soilless plant cultivation systems. Wood biochar could entirely or partly substitute peat as a plant growing constituent to produce vegetables. Nevertheless, knowledge concerning potential plant performance of leafy green vegetables grown on wood biochar is restricted. The present study assessed the main physicochemical traits of various growing media constituted by decreasing the content of peat and by increasing the percentages of poplar wood biochar. Yield, nutritional and functional properties of curly endive plants cultivated in a protected environment were also tested. Biochar was pyrolyzed from poplar (Populus nigra L.) at 450 or 700 °C for 48 h. Increasing biochar concentration and pyrolysis temperature resulted in higher pH, EC and K content of the growing mediums. Biochar was also effective in increasing particle density and bulk density. Biochar at 70% and pyrolysis temperature of 450 °C significantly increased head fresh weight by 47.4%, head height by 24.9%, stem diameter by 21.5% and number of leaves by 80.8%, respectively compared with the control (100% peat). Head dry matter content, root dry matter content, SSC, ascorbic acid and total phenolic were also significantly affected by this treatment. Furthermore, the addition of biochar and the use of higher pyrolysis temperature decreased N leaves concentration. This represents a particularly important target for leafy green vegetables healthiness.

Role of cotton sticks biochar in immobilization of nickel under induced toxicity condition and growth indices of Trigonella corniculata L

Among various heavy metals, nickel (Ni) is a potential pollutant that accumulates in broad-leaf vegetables and is reported to be carcinogenic. Biochar (BC) is a nutrient-rich and effective organic amendment for immobilization of Ni in soil. Fenugreek (Trigonella corniculata L.), a broad-leaf vegetable, is commonly cultivated due to its all-inclusive composition of nutrients such as calcium and iron and β-carotene and vitamins. Therefore, a field-pot study was conducted to examine the effectiveness of cotton-sticks-waste biochar (BC) for soil immobilization of Ni in fenugreek crop cultivated between early-October to end-November 2015. Fenugreek was grown in a sandy-loam soil experimentally contaminated with various Ni levels (0, 25, 50, and 100 mg Ni kg^-1 soil) under three BC levels (0, 3, and 5%; w/w). Overall, results showed increasing plant lipid peroxidation (assessed via malondialdehyde) and ascorbic-acid concentration with increasing Ni toxicity level without BC application (p ≤ 0.05). Application of 3% BC increased the chlorophyll a (20.0%), chlorophyll b (49.1%), total chlorophyll (27.6%), carotenoids (21.6%), anthocyanin (27.2%), photosynthetic rate (112%), transpiration rate (45.0%), and sub-stomatal CO₂ concentration (19.9%) in fenugreek as compared to control (0% BC) under 50 mg Ni kg^-1 soil. Higher BC application rate (5%) was more effective in increasing the chlorophyll a (33.6%), chlorophyll b (81.1%), total chlorophyll (43.9%), carotenoids (71.7%), anthocyanin (77.8%), photosynthetic rate (127%), transpiration rate (42.2%), and sub-stomatal CO₂ concentration (23.5) over control under 100 mg Ni kg^-1 soil. We suggest that the consistent increases in dry mass, carbon flux rate and, protein, amino acids, and sugar contents of fenugreek (cultivated in a soil toxified with Ni and amended with 5% BC) seems to be caused by the reduction in the mobility of Ni in the presence of BC in a sandy-loam soil.