Phytoremediation Potential Research Articles

Leaf surface functional traits influence particulate matter and polycyclic aromatic hydrocarbons air pollution mitigation: Insights from Mediterranean urban forests

In this work the leaf surface functional traits, potentially useful for air phytoremediation of particulate matter (PM) and polycyclic aromatic hydrocarbons (PAH), of 28 woody species have been characterized, and the role of these stomata, trichomes and cuticle traits in phytoremediation have been assessed looking at existing correlations with species-specific ability to sequester and retain airborne pollutants. Leaves were sampled in urban area in August and September and functional traits were measured using Scanning Electron Microscopy and Fourier-transform infrared spectroscopy. Pollutants were extracted by leaves and their concentrations and daily uptake rates were measured using gas chromatography. Significant differences were found between species in the arrangement of functional traits, concentrations and daily uptake of pollutants. Correlations between variables were studied by means of principal component analysis. The trichomes-related traits scaled positively with PM concentration daily uptake, whereas for PAH air phytoremediation, the cuticle physical and chemical features are relevant. Trichomes increase the leaf area several fold providing extra surfaces for PM retention, while cuticle thickness and esterification regulate the PAH retention and translocation in subcuticular tissues. Results provide novelty on the relationships between leaf surface functional traits and plant species phytoremediation potential, outlining an innovative way of measuring leaf surface functional traits. In addition to broadening the economic spectrum of functional traits, it is emphasized how important leaf surface functional traits are in the nature-based solutions definition and planning.

Phytoremediation of cadmium-trichlorfon co-contaminated water by Indian mustard (Brassica juncea): growth and physiological responses

In this study, the morphological and physiological responses of Brassica juncea to the stresses of Cadmium (Cd) and trichlorfon (TCF), and the phytoremediation potential of B. juncea to Cd and TCF were investigated under hydroponics. Results showed that Cd exhibited strong inhibition on biomass and root morphology of B. juncea as Cd concentration increased. The chlorophyll a fluorescence intensity and chlorophyll content of B. juncea decreased with the increased Cd concentration, whereas the malondialdehyde and soluble protein contents and superoxide dismutase activity increased. TCF with different concentrations showed no significant influence on these morphological and physiological features of B. juncea. The biomass and physiological status of B. juncea were predominantly regulated by Cd level under the co-exposure of Cd and TCF. B. juncea could accumulate Cd in different plant parts, as well as showed efficient TCF degradation performance. A mutual inhibitory removal of Cd and TCF was observed under their co-system. The present study clearly signified the physiological responses and phytoremediation potential of B. juncea toward Cd and TCF, and these results suggest that B. juncea can be used as an effective phytoremediation agent for the Cd-TCF co-contamination in water.

Phytoremediation Potential of <i>Ficus Benjamina</i> for the removal of Naphthalene, Acenaphthene and Phenanthrene in Contaminated Soil

This study was undertaken to evaluate the phytoremediation potential of Ficus Benjamina plant for the removal of polycyclic aromatic hydrocarbons (PAHs): Acenaphthene (ACN), naphthalene (NAP) and phenanthrene (PHE) from contaminated soil. The plant was transplanted into pot containing 4 kg soil spiked with the PAHs: ACN, NAP and PHE at concentrations of 1600, 2000 and 2400 mg respectively. A separate pot with untreated soil was used as a control. Irrigation was done with 600 mL of water after every three days in the evening hours for eight weeks. Samples of the plant and soil were collected at the end of the phytoremediation process; the plant was washed with tap water and carefully separated into roots and shoots, dried along with the soil, ground and sieved. The sieved soil, roots, shoots of the experimental plant as well as that of the control were analyzed for the levels of PAHs: ACN, NAP and PHE following Soxhlet extraction with 200 mL of dichloromethane-acetone (1:1 v/v) at 60 oC for 6 hours using high performance liquid chromatography (HPLC). The bioconcentration factor (BCF) in mg/kg and the Translocation Factor (TF) in mg/kg of Ficus Benjamina for ACN, NAP and PHE were (1.76 and 0.47), (0.54 and 2.7) and (0.93 and 0.68) respectively. The results generated in this study have demonstrated that the different concentrations of the PAHs (NAP, ACN and PHE) in root, only NAP was transferred to the aerial parts of the plant and this suggests the suitability of Ficus Benjamina for the phytoremediation of NAP.

Assessment of Vinca rosea (Apocynaceae) Potentiality for Remediation of Crude Petroleum Oil Pollution of Soil

Petroleum oil pollution is a worldwide problem that results from the continuous exploration, production, and consumption of oil and its products. Petroleum hydrocarbons are produced as a result of natural or anthropogenic practices, and their common source is anthropogenic activities, which impose adverse effects on the ecosystem’s nonliving and living components including humans. Phytoremediation of petroleum hydrocarbon-polluted soils is an evolving, low-cost, and effective alternative technology to most traditional remediation methods. The objective of this study is to evaluate the phytoremediation potentiality of Vinca rosea for crude oil-contaminated soil by understanding its properties and involvement in the enhanced degradation of crude oil. The remediation potentiality was determined by evaluating the total petroleum hydrocarbon degradation percentage (TPH%) and changes in the molecular type composition of saturated and aromatic hydrocarbon fractions. TPH% was estimated gravimetrically, and changes in the molecular type composition of saturated and aromatic fractions were measured using gas chromatography and high-performance liquid chromatography, respectively. Sulfur concentration was measured using X-ray fluorescence. Cadmium and lead quantification was measured using Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). The results revealed that V. rosea enhanced total petroleum hydrocarbon (TPH) degradation and altered the molecular composition of the crude oil. The saturated hydrocarbons increased and the aromatic hydrocarbons decreased. The saturated hydrocarbon fraction in the crude oil showed a wider spectrum of n-paraffin peaks than the oil extracted from unplanted and V. rosea-planted soils. Polyaromatic hydrocarbon degradation was enhanced in the presence of V. rosea, which was reflected in the increase of monoaromatic and diaromatic constituents. This was parallel to the increased sulfur levels in planted soil. The determination of sulfur and heavy metal content in plant organs indicated that V. rosea can extract and accumulate high amounts from polluted soils. The ability of V. rosea to degrade TPH and alter the composition of crude petroleum oil by decreasing the toxicity of polyaromatic hydrocarbons in soil, as well as its capability to absorb and accumulate sulfur and heavy metals, supports the use of plant species for the phytoremediation of crude oil-polluted sites.

Transcriptome-Wide Identification and Response Pattern Analysis of the Salix integra NAC Transcription Factor in Response to Pb Stress.

The NAC (NAM-ATAF1/2-CUC) transcription factor family is one of the largest plant-specific transcription factor families, playing an important role in plant growth and development and abiotic stress response. As a short-rotation woody plant, Salix integra (S. integra) has high lead (Pb) phytoremediation potential. To understand the role of NAC in S. integra Pb tolerance, 53 SiNAC transcripts were identified using third-generation and next-generation transcriptomic data from S. integra exposed to Pb stress, and a phylogenetic analysis revealed 11 subfamilies. A sequence alignment showed that multiple subfamilies represented by TIP and ATAF had a gene that produced more than one transcript under Pb stress, and different transcripts had different responses to Pb. By analyzing the expression profiles of SiNACs at 9 Pb stress time points, 41 of 53 SiNACs were found to be significantly responsive to Pb. Short time-series expression miner (STEM) analysis revealed that 41 SiNACs had two significant Pb positive response patterns (early and late), both containing 10 SiNACs. The SiNACs with the most significant Pb response were mainly from the ATAF and NAP subfamilies. Therefore, 4 and 3 SiNACs from the ATAF and NAP subfamilies, respectively, were selected as candidate Pb-responsive SiNACs for further structural and functional analysis. The RT-qPCR results of 7 transcripts also confirmed the different Pb response patterns of the ATAF and NAP subfamilies. SiNAC004 and SiNAC120, which were randomly selected from two subfamilies, were confirmed to be nuclear localization proteins by subcellular localization experiments. Functional prediction analysis of the associated transcripts of seven candidate SiNACs showed that the target pathways of ATAF subfamily SiNACs were "sulfur metabolism" and "glutathione metabolism", and the target pathways of NAP subfamily SiNACs were "ribosome" and "phenylpropanoid biosynthesis". This study not only identified two NAC subfamilies with different Pb response patterns but also identified Pb-responsive SiNACs that could provide a basis for subsequent gene function verification.

Field-Scale Floating Treatment Wetlands: Quantifying Ecosystem Service Provision from Monoculture vs. Polyculture Macrophyte Communities

Global water security is critical for human health, well-being, and economic stability. However, freshwater environments are under increasing anthropogenic pressure and now, more than ever, there is an urgent need for integrated approaches that couple issues of water security and the remediation of degraded aquatic environments. One such strategy is the use of floating treatment wetlands (FTW), which are artificial floating mats that sustain and support the growth of macrophytes capable of removing nutrients from over-enriched waterbodies. In this study, we quantify a range of indicators associated with FTWs, planted with different vegetation community types (i.e., monocultures and polycultures) over the course of a three-year field-scale study. The composition of the two different types of FTWs changed significantly with a convergence in diversity and community composition between the two types of FTWs. Phytoremediation potential of the two FTW communities, in terms of nutrient standing stocks, were also similar but did compare favourably to comparable wild-growing plant communities. There were few substantial differences in invertebrate habitat provision under the FTWs, although the high incidence of predators demonstrated that FTWs can support diverse macroinvertebrate communities. This field-scale study provides important practical insights for environmental managers and demonstrates the potential for enhanced ecosystem service provision from employing nature-based solutions, such as FTWs, in freshwater restoration projects.

Bioaccumulation of potentially toxic elements by indigenous and exotic trees growing around a copper leaching plant in Mufulira, Zambia

Potentially toxic elements (PTEs) from mining industries pollute the surrounding environment and threaten the health of communities. Worldwide, exotic and indigenous trees are being recommended for green belts to trap dust and thereby limit the dispersion of PTEs. This study compares the potential of exotic (Eucalyptus grandis and E. camaldulensis) and native (Brachystegia longifolia) tree species in Zambia to accumulate PTEs and evaluate their ability to biomonitor heavy metal pollution. Tree bark and leaf samples were collected from 10 trees per study species growing at the same site downwind from a copper-leaching plant. Thirty topsoil samples were collected one metre from each sampled tree trunk. Portable X-ray fluorescence was used to analyse the elemental composition and concentration of trace elements in plant and soil samples. Pollution indices were used to establish the status and degree of soil contamination, while the bioaccumulation factor determined the ability of the studied species to accumulate PTEs. Heavy metals, including Mn, Ni, Pb, Cd, Cu, Fe and Zn were detected across soil and biomass samples, with a significant variation between species and plant parts. The pollution indices established that the soil at the study site is highly contaminated with Cu. The concentration of the studied trace elements varied across species following the order E. grandis > B. longifolia > E. camaldulensis in both tree bark and leaves. Determined bioaccumulation factors indicated Cd, Mn and Zn accumulation abilities of all the studied species suggesting their biomonitoring and phytoremediation potential. This implies that the study species have the potential to biomonitor Cd, Mn and Zn. Furthermore, a higher concentration of Cu was detected in B. longifolia bark, suggesting that this tree species can be used to biomonitor Cu pollution attributed to emissions from industrial activities. This study presents new insights into improving the management of polluted environments through biomonitoring and bioaccumulation of PTEs which can guide the selection of appropriate species for greenbelts in industrial areas.

Chinese sapindaceous tree species (Sapindus mukorosii) exhibits lead tolerance and long-term phytoremediation potential for moderately contaminated soils

Heavy metal pollution in metropolitan soils poses significant risks to human health and the entire ecosystem. Effective mitigation strategies and technologies are crucial for addressing these environmental issues. Fast-growing trees are an essential part of phytoremediation projects all over the world and provide long-term ecological benefits to mankind. This study assessed the lead tolerance and phytoremediation potential of a fast-growing soapberry tree species (Sapindus mukorossi) in moderately contaminated soil. Two independent experiments were conducted to assess its tolerance at (i) germination level and (ii) prolonged growth stage. In the germination experiments, seeds were exposed to lead (II) nitrate Pb (NO₃)₂ at various concentrations (0, 5, 10, 20, 50, 100, 200, 300, 400 and 500 μM) for 120 days. Results showed significant differences in germination time, germination index, seedling vigor index, energy of germination, final germination, germination inhibition, seedling height and root/shoot weight compared to the control experiments. In the prolonged growth experiments, seedlings were grown for six months in soils amended/spiked with different Pb concentrations (T0 = 0, T1 = 20, T2 = 50, T3 = 100, T4 = 150 and T5 = 200 mg kg−1 soil) and their biomass was determined. The highest biomass achieved in six months (T0: 12.62 g plant−1), followed by (T1: 12.33 g plant−1), (T2: 12.42 g plant−1), (T3: 11.86 g plant−1), (T4: 10.86 g plant−1) and (T5: 10.06 g plant−1) respectively. S. mukorossi showed no visible signs of Pb toxicity over a six-month period. During six months of exposure, the total Pb content in S. mucrossi tissues were classified as roots > leaves > stems. The highest cumulative absorption of Pb occurred between the fourth and fifth months of exposure. Maximum transfer factor (TF) was detected during the fourth month ranging from 0.888 to 1.012 for the different Pb concentrations. Furthermore, the growth behavior, lead accumulation, bioconcentration factors (BCF) and tolerance index (TI) indicated that S. mucrossi may tolerate moderate Pb concentrations for longer periods. These findings suggest that S. mukorossi may be deployed for long-term phytoremediation coupled with urban forest applications in the future.

Effect of sodium alginate–gelatin–polyvinyl pyrrolidone microspheres on cucumber plants, soil, and microbial communities under lead stress

Lead is highly persistent and toxic in soil, hindering plant growth. Microspheres are a novel, functional, and slow-release preparation commonly used for controlled release of agricultural chemicals. However, their application in the remediation of Pb-contaminated soil has not been studied; furthermore, the remediation mechanism involved has not been systematically assessed. Herein, we evaluated the Pb stress mitigation ability of sodium alginate–gelatin–polyvinyl pyrrolidone composite microspheres. Microspheres effectively attenuated the Pb toxic effect on cucumber seedlings. Furthermore, they boosted cucumber growth, increased peroxidase activity, and chlorophyll content, while reducing malondialdehyde content in leaves. Microspheres promoted Pb enrichment in cucumber, especially in roots (about 4.5 times). They also improved soil physicochemical properties, promoted enzyme activity, and increased soil available Pb concentration in the short term. In addition, microspheres selectively enriched functional (heavy metal-tolerating and plant growth promoting) bacteria to adapt to and resist Pb stress by improving soil properties and nutrients. These results indicated that even a small amount (0.025–0.3 %) of microspheres can significantly reduce the adverse effects of Pb on plants, soil, and bacterial communities. Composite microspheres have shown great value in Pb remediation, and their application potential in phytoremediation is also worth evaluating to expand the application.

Co-application of citric acid and Nocardiopsis sp. strain RA07 enhances phytoremediation potentiality of Sorghum bicolor L.

This study investigated the combined effects of citric acid (CA) and Nocardiopsis sp. RA07 on the phytoremediation potential of lead (Pb)- and copper (Cu)-contaminated soils by Sorghum bicolor L. The strain RA07 was able to tolerate Pb and Cu, and exhibited plant growth-promoting features like siderophore production, indole-3-acetic acid (IAA) synthesis, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity and phosphate solubilization. The combined application of CA andstrain RA07 significantly increased S. bicolor growth, chlorophyll content and antioxidant enzymatic activity, and decreased oxidative stress (hydrogen peroxide and malondialdehyde content) under Pb and Cu stress circumstances as compared to individual treatments (i.e., CA and strain RA07). Furthermore, the combined application of CA and RA07 significantly enhanced S. bicolor ability to accumulate Pb and Cu by 64.41% and 60.71% in the root and 188.39% and 125.56% in the shoot, respectively, as compared to the corresponding uninoculated plants. Our results indicate that inoculation of Nocardiopsis sp. together with CA could be a useful practical approach to mitigate Pb and Cu stress on plant growth and increase the effectiveness of phytoremediation in Pb- and Cu-polluted soils.

Pharmaceutical, cosmeceutical, food additive and agricultural perspectives of Cymbopogon martini: A potential industrial aromatic crop

Magnifying the productivity of Medicinal and Aromatic Plants (MAPs) ultimately relies on the ability to scale from Farm to Laboratory and Laboratory to Industry. Cymbopogon martini (Roxb.) W.Watson (Poaceae), popularly known as palmarosa, Indian geranium, ginger-grass, and rosha-grass is rich in volatile secondary metabolites having an industrial perspective. In this review article, we provide a comprehensive assessment of the industrial application of C. martini and its potential in the pharmaceutical, cosmeceutical, food industries, and its agriculture perspective in terms of its potential in phytoremediation and land restoration. We have attempted to put all the material accessible in the literature about C. martini and its volatile metabolites for various industrial applications. Electronic databases such as Science Direct, PubMed, Google Scholar, Web of Science, Ethnobotany, Academic Journals, and library searches were used to assemble the available data. According to the published literature, the essential oil of C. martini is rich in cyclic and acyclic monoterpenoids which has a wide range of pharmaceutical, cosmeceutical, food additive, and agricultural applications due to anti-microbial, anti-oxidant, anti-inflammatory, anti-diabetic, wound healing, cardioprotective, neuroprotective, anthelmintic, insecticidal, larvicidal, acaricidal, nematicidal and herbicidal activities. The cultivation of C. martini has shown additional benefits in terms of restoration of productivity and functions of wasteland through the phytoremediation process. This review article provides first-time updated information about C. martini as a potential bio-resource for utilization of wastelands with special reference to its industrial potential.

Iron Accumulation of Halophytes on the White Sea Littoral Zone

The accumulation of iron in halophytic species Triglochin maritima L., Plantago maritima L., Aster tripolium L. and Zostera marina L. was studied in this research. Littoral soils are not contaminated with iron (6–16 g/kg). Seawater, on contrary, contains high concentrations of iron (0.04–0.32 mg/l). Halophytes accumulate iron to supervalues (6.49–71.63 г/кг), 93% of metal is found in rhyzomes. The reasons for this phenomenon are discussed. Halophytes of the White Sea littoral zone are involved in the biogeochemical iron cycle as the main fixation sites of iron in the system “coast–sea”. They have phytoremediation potential on the coastal territories.

Riparian Vegetation Assessment for Effective Management of Molawin River, Mt. Makiling, Philippines

Molawin River is experiencing water quality degradation over time. Efforts were made to help rehabilitate this river to maintain its ecology and biodiversity. The main objectives of this research are: to identify and document water filtering plants (riparian flora) both present in terrestrial and aquatic ecosystems in the Molawin River and to pinpoint the sources and community perception that defies the idea of riparian flora species as potential water filtering plants in the Molawin River. Documentation of dense riparian flora present in the Molawin River was conducted in order to study its phytoremediation potential for water purification. A total of 107 morpho-species belonging to 94 genera from 56 families was recorded. The most common flora species was Commelina diffusa, Cyperus flabelliformis and Costus speciosus. A household survey and key informant interview were employed. The idea of riparian flora as a potential water purifying plants is facing four main challenges. First, there is a low conservation interest with the water resource, as this is not the primary source of water for them. Secondly, the presence of anthropogenic factors severely affecting the area. Thirdly, the high rate of encroachment of the invasive plants aggravates the conditions of the river. Finally, the lack of institutional support that can integrate riparian flora species in watershed management and rehabilitation planning.

Phytoremediation of chloride from marine dredged sediments: A new model based on a natural vegetation recolonization

Phytoremediation is a type of bioremediation process that involves the use of plants to remove or degrade contaminants from soil, water, or air. In most of the observed phytoremediation models, plants are introduced and planted on a polluted site to take up, absorb, or transform contaminants. This study aims to explore a new mixed phytoremediation approach that involves natural recolonization of a contaminated substrate, by identifying the species growing naturally, their bioaccumulation capacity, and by modeling annual mowing cycles of their aerial parts. This approach aims to evaluate the phytoremediation potential of such a model. Both natural and human interventions are involved in this approach, which is referred to as a mixed phytoremediation process. The study focuses on chloride phytoremediation from a chloride-rich and regulated substrate that is marine dredged sediments abandoned for 12 years and recolonized for 4 years. The sediments are colonized by a Suaeda vera dominated vegetation and possess heterogeneity in lixiviate chloride and conductivity. The study found that despite Suaeda vera is the well adapted species for this environment, it is not an effective species for phytoremediation as it has low bioaccumulation and translocation rates (9.3 and 2.6 respectively), and disturbs chloride leaching below in the substrate. Other identified species, such as Salicornia sp., Suaeda maritima, and Halimione portulacoides, have better phytoaccumulation (respectively 39.8, 40.1, 34.8) and translocation rates (respectively 7.0, 4.5, 5.6) and can successfully remediate the sediment in 2–9 years. The following species have been found to bioaccumulate chloride in aboveground biomass at the following rates: Salicornia sp. (181 g/kg DW), Suaeda maritima (160 g/kg DW), Sarcocornia perennis (150 g/kg DW), Halimione portulacoides (111 g/kg DW) and Suaeda vera (40 g/kg DW).

Evaluation of plant species for air pollution tolerance and phytoremediation potential in proximity to a coal thermal power station: implications for smart green cities.

In metropolitan areas, air pollution poses a significant threat, and it is crucial to carefully select plant species that can tolerate such conditions. This requires a scientific approach based on systematic evaluation before recommending them to executive bodies. This study aimed to determine the air pollution tolerance index (APTI), dust retention capacity, and phytoremediation ability of 10 plant species growing in and around a lignite-based coal thermal power station. The results showed that Ficus benghalensis L. had the highest APTI, followed by Mimusops elengi L., Ficus religiosa L., Azadirachta indica A. Juss., and Annona reticulata L. F. benghalensis also showed the highest pH of leaf extract, relative water content, total chlorophyll, and ascorbic acid content, as well as the highest dust capturing capacity. Among the ten plant species, F. benghalensis, M. elengi, F. religiosa, A. indica and F. racemosa were identified as a tolerant group that can be used for particulate matter suppression and heavy metal stabilization in and around thermal power plants. These findings can inform the selection of plants for effective green infrastructure in smart green cities, promoting the health and well-being of urban populations. This research is relevant to urban planners, policymakers, and environmentalists interested in sustainable urban development and air pollution mitigation.

Effect of iron-loaded sludge biochar amendments on phytoremediation potential of Cr-contaminated soils by Leersia hexandra swartz

In this study, the effect of iron-loaded sludge biochar (ISBC) with different amendment dosages (mass ratio of biochar to soil equal to 0, 0.01, 0.025 and 0.05) on the phytoremediation potential of Leersia hexandra swartz (L. hexandra) to Cr-contaminated soil was investigated. With increasing ISBC dosage from 0 to 0.05, plant height, aerial tissue biomass and root biomass increased from 15.70 cm, 0.152 g pot−1 and 0.058 g pot−1 to 24.33 cm, 0.304 g pot−1 and 0.125 g pot−1, respectively. Simultaneously, the Cr contents in aerial tissues and roots increased from 1039.68 mg kg−1 to 2427.87 mg kg−1 to 1526.57 mg kg−1 and 3242.62 mg kg−1, respectively. Thus, the corresponding bioenrichment factor (BCF), bioaccumulation factor (BAF), total phytoextraction (TPE) and translocation factor (TF) values were also increased from 10.52, 6.20, 0.158 mg pot−1 (aerial tissue)/0.140 mg pot−1 (roots) and 0.428 to 15.15, 9.42, 0.464 mg pot−1 (aerial tissue)/0.405 mg pot−1 (roots) and 0.471, respectively. The significant positive effect of ISBC amendment was primarily attributed to the following three aspects: 1) the root resistance index (RRI), tolerance index (TI) and growth toxicity index (GTI) of L. hexandra to Cr were increased from 100%, 100% and 0%–216.88%, 155.02% and 42.18%, respectively; 2) the bio-available Cr content in the soil was decreased from 1.89 mg L−1 to 1.48 mg L−1, while the corresponding TU (toxicity units) value was declined from 0.303 to 0.217; 3) the activities of urease, sucrase and alkaline phosphatase in soil were increased from 0.186 mg g−1, 1.40 mg g−1 and 0.156 mg g−1 to 0.242 mg g−1, 1.86 mg g−1 and 0.287 mg g−1, respectively. In summary, ISBC amendment was able to significantly improve the phytoremediation of Cr-contaminated soils by L. hexandra.

Effects of novel Cd mobilization bacteria and bone meal on the structure and function of soil bacterial communities and cadmium phytoremediation potential

Phytoremediation techniques for heavy metals in soils are inefficient due to phytotoxicity and low bioavailability of heavy metals in soils. Therefore, it is crucial to improve the bioavailability of cadmium (Cd) in soils and plant biomass. In this study, bacteria (L8) with high tolerance to heavy metals were isolated and screened from landfills. Bone meal (BM) was used as an organic amendment to form a synergistic enhancement system with L8 to improve the efficiency of phytoextraction of Cd from soil. A total of four treatments were set up: Control treatment (CK), L8 treatment (T1), 0.5% bone meal treatment (T2), and 0.5% bone meal + L8 treatment (T3). Compared with CK, ryegrass biomass and Cd accumulation in the T3 treatment group increased by 28.36% and 131.81%, respectively. Microbiome and metabolome analyses showed that the combination of bone meal and L8 significantly altered the inter-root microbial community and increased the levels of metabolites associated with the stress response. The combination of bone meal and L8 increased ryegrass biomass and plant detoxification. This was mainly attributed to an increase in the content of amino acids, esters, carbohydrates and sugars in the soil, as well as an increase in antioxidants and soil enzyme activity associated with stress tolerance.The results of this study provide novel insights into efficient remediation of heavy metals in soils, and present a simple and environmentally friendly method to facilitate the mobilization and phytoextraction of Cd from contaminated soils.

Heavy metals and nutrients removal in a batch-fed greywater treatment system planted with Canna indica and Oryza sativa L.

The objective of this investigation was to determine whether Canna indica and Oryza sativa L. plants have the phytoremediation potential for removing heavy metals and nutrients from greywater treated in batch-fed Horizontal sub-surface Flow Constructed Wetlands (HssFCW). The HssFCW had a Hydraulic Retention Time (HRT) and organic loading rate (OLR) of 3 days and 3.96 (g.BOD/m2.day) respectively. Greywater (GW) samples were characterized for electrical conductivity (EC), total nitrogen (TN), total phosphorous (TP), pH, sodium adsorption ratio (SAR), metals (Al, Fe, Mg, Ca) and Biochemical Oxygen Demand (BOD5). The accumulation of metals in the soil and edible parts of plants was evaluated in terms of bioconcentration and translocation factors. Metal concentrations were determined using an atomic absorption spectrometer, while nutrients were by colorimetric method. The result shows that the metals and nutrients were below the WHO allowable limit for treated greywater recycling in agriculture. Nutrient removal was insignificantly different while metal removal was significantly different in the constructed wetlands (CW). The results indicated that C. indica is preferred as a perennial plant with unlimited metal accumulation and high nutrient removals compare to O. sativa L. with a high metal concentration in the above-ground plant tissue and also an annual plant.

Understanding physiological and molecular adaptations of three diverse halophytic grasses under saline and sodic stresses

Physiological and biochemical analyses of three halophytes were conducted to explore their tolerance and phytoremediation potential. The halophytes Urochondra setulosa, Sporobolus marginatus and Leptochloa fusca were categorised based on gas exchange attributes, antioxidant system, biomass production under soil salinity (ECe 30-50 dS/m) and sodicity (pH 9.5-10). L. fusca and S. marginatus produced slightly higher biomass under the sodic condition of pH 9.5, while in U. setulosa, it increased under salinity stress. Under sodic conditions, L. fusca showed less reduction in potassium content and maintained a higher K+/Na+ ratio in their leaf tissues. A maximum decrease in net photosynthesis was observed in L. fusca (28.55%) at ECe ~ 50 dS m-1 while minimum in S. marginatus (13.73%) at pH ~ 10.0. Comparatively, U. setulosa showed higher stomatal conductance and transpiration rate than L. fusca and S. marginatus. At the highest pH and salinity, the antioxidant activities of enzymes APX, SOD, GR and POX increased in all three halophytes. Quantitative expression of MnSOD, NHX1 and FuSOS1 genes in all three halophytes increased with salt stresses. Based on these indicators, these halophytes were categorised as salt-tolerant or alkaline-stress-tolerant.

Endophytic Bacillus sp. AP10 harboured in Arabis paniculata mediates plant growth promotion and manganese detoxification

Phytoremediation of heavy metal-polluted soils assisted by plant-associated endophytes, is a suitable method for plant growth and manganese (Mn) removal in contaminated soils. This investigation was conducted to evaluate the Mn-resistant endophytic resources of the Mn hyperaccumulator Arabis paniculata and their functions in the phytoremediation of Mn2+ toxicity. This study isolated an endophytic bacterium with high Mn resistance and indole-3-acetic acid (IAA) production form A. paniculata and identified it as Bacillus sp. AP10 using 16 S rRNA gene sequencing analysis. The effects of Bacillus sp. AP10 on the alleviation of Mn2+ toxicity in Arabidopsis thaliana seedlings and the molecular mechanisms were further investigated using biochemical tests and RNA-seq analysis. Under Mn2+ stress, Bacillus sp. AP10 increased the biomass, chlorophyll content and the translocation factor (TF) values of Mn in the aerial parts, while decreased the malondialdehyde (MDA) content of A. thaliana seedlings compared with that of control plants. The differentially expressed genes (DEGs) and enrichment analysis showed that Bacillus sp. AP10 could significantly increase the expression of key genes involved in cell-wall loosening, which may improve plant growth under Mn stress. Superoxide dismutase (SOD)-encoding genes were detected as DEGs after AP10 treatment. Moreover, AP10 regulated the expression of genes responsible for phenylpropanoid pathway, which may promote antioxidant flavonoids accumulation for reactive oxygen species (ROS) scavenging to improve Mn tolerance. The activation of ATP-binding cassette (ABC) transporter gene expression especially ABCB1 after AP10 stimulation, explained the elevation of metal ion binding or transport related to enhanced Mn accumulation in plants. Futhermore, AP10 might alleviate Mn toxicity through enhancing abscisic acid (ABA) responsive gene expression and ABA biosynthesis. These findings provide new insights into the functions and regulatory mechanism of Bacillus sp. AP10 in promoting plant growth, and tolerance, improving Mn accumulation and alleviating Mn2+ toxicity in plants. The application of Bacillus sp. AP10 as potential phytoremediators may be a promising strategy in Mn2+ contaminated fields. Availability of data and materialsThe datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.