Bioaugmented Phytoremediation of Metal-Contaminated Soils and Sediments by Hemp and Giant Reed

Industrial hemp (Cannabis sativa L.) can utilize and remediate soil strongly contaminated with Cu, As, Cd, and Pb by phytoattenuation

Industrial hemp (Cannabis sativa L.) has great application potential in heavy metal-polluted soils owing to its safe non-food utilization. However, the fate of heavy metals in different varieties of hemp planted in strongly contaminated natural soils remains unknown. Here, we investigated the growth, heavy metal uptake, distribution, and transfer of nine hemp varieties in soils strongly contaminated with Cu, As, Cd, and Pb. Hemp variety and metal type were the main factors affecting the growth and heavy metal uptake in hemp. The nine hemp varieties grew well in the contaminated soils; however, differences existed among the varieties. The biomass of Z3 reached 5669.1 kg hm-1, whereas that of Yunma No. 1 was only 51.8 % of Z3. The plant height, stalk diameter, and stalk bark thickness of Z3 were greater than those of the other varieties, reaching 168 cm, 9.2 mm, and 0.56 mm, respectively. Permanova's analysis revealed that the total effects of Cu, As, Cd, and Pb on the growth of the nine hemp varieties reached 60 %, with leaf As having the greatest effect, reaching 16 %. , Even in strongly contaminated soils, the nine varieties showed poor Cu, As, Cd, and Pb uptake. Most of the Cu, As, Cd, and Pb were retained in the root, reaching 57.7-72.4, 47.6-64.7, 76.0-92.9, and 70.0-87.8 %, respectively. Overall, the Cu, As, Cd, and Pb uptake of Wanma No.1 was the highest among the nine varieties, whereas that of Guangxi Bama was the lowest. These results indicate that hemp is a viable alternative for phytoattenuation in soils contaminated with heavy metals because of its ability to tolerate and accumulate Cu, As, Cd, and Pb in its roots, and Guangxi Bama is superior to the other varieties considering the safe utilization of hemp products.

Phosphate-solubilizing bacteria improve the antioxidant enzyme activity of Potamogeton crispus L. and enhance the remediation effect on Cd-contaminated sediment

Phosphorus-solubilizing bacteria (PSB) assisted phytoremediation of cadmium (Cd) pollution is an effective method, but the mechanism of PSB-enhanced in-situ remediation of Cd contaminated sediment by submerged plants is still rare. In this study, PSB (Leclercia adecarboxylata L1-5) was inoculated in the rhizosphere of Potamogeton crispus L. (P. crispus) to explore the effect of PSB on phytoremediation. The results showed that the inoculation of PSB effectively improved the Cd extraction by P. crispus under different Cd pollution and the Cd content in the aboveground and underground parts of P. crispus all increased. The μ-XRF images showed that most of the Cd was enriched in the roots of P. crispus. PSB especially showed positive effects on root development and chlorophyll synthesis. The root length of P. crispus increased by 51.7 %, 80.5 % and 74.2 % under different Cd pollution, and the Ca/Cb increased by 38.9 %, 15.2 % and 8.6 %, respectively. Furthermore, PSB enhanced the tolerance of P. crispus to Cd. The contents of soluble protein, MDA and H2O2 in 5 mg·kg-1 and 7 mg·kg-1 Cd content groups were decreased and the activities of antioxidant enzymes were increased after adding PSB. The results showed that the application of PSB was beneficial to the in-situ remediation of submerged plants.

Phytoremediation of contaminated sediment combined with biochar: Feasibility, challenges and perspectives

The accumulation of contaminants in sediments is accelerated by human activities and poses a major threat to ecosystems and human health. In recent years, various remediation techniques have been developed for contaminated sediments. In this review, a bibliometric analysis of papers on sediment remediation indexed in the WOS database between 2009 and 2023 was conducted using VOSviewer. We describe the development of biochar and plants for sediment contaminant removal. However, the single processes of biochar remediation and phytoremediation can be impeded by (i) low efficiency, (ii) poor tolerance of plants towards pollutants, (iii) difficulty in biochar to degrade pollutants, and (iv) biochar aging causing secondary pollution. Fortunately, combination remediation, realized through the combination of biochar and plants, can overcome the shortcomings of their individual applications. Therefore, we suggest that the remediation of contaminants in sediments can be accomplished by combining biochar with macrophytes and considering multiple limiting factors. Here, we explore the challenges that co-remediation with biochar and macrophytes will face in achieving efficient and sustainable sediment remediation, including complex sediment environments, interaction mechanisms of biochar-macrophyte-microorganisms, emerging pollutants, and integrated life cycle assessments, which can provide references for combined biochar and plant remediation of sediments in the future.

The comprehensive review about elements accumulation in industrial hemp (Cannabis sativa L.)

Cannabis sativa L., commonly known as industrial hemp, is a versatile plant with applications ranging from medicinal to agricultural and industrial uses. Despite its benefits, there is a notable gap in regulatory toxicology, in understanding the extent of element accumulation in hemp, which is critical due to its ability to absorb various elements from the soil, including heavy metals (Pb, Cd, Hg, and As), uptakes potential toxic elements (e.g., Sb, Sn, Sr, Bi, Tl), problematic elements (Ni, Cr, Co), and essential elements (Zn, Cu, Fe, Mn). The paper aims to enrich current understandings by offering a comprehensive analysis of elements absorption in industrial hemp. This study emphasizes the potential health risks linked with hemp consumption including regulatory toxicology aspects: limits, Permitted Daily Exposures (PDE), recommendations in different countries and from different agencies/bodies (like the WHO and the EU) based on route of administration, jurisdiction and actual literature review. This review contributes significantly to the knowledge base on hemp safety, serving as a valuable resource for researchers, regulatory bodies, and industry stakeholders.

Elucidating the significant roles of root exudates in organic pollutant biotransformation within the rhizosphere

Biotransformation of organic pollutants is crucial for the dissipation of environmental pollutants. While the roles of microorganisms have been extensively studied, the significant contribution of various root exudates are still not very well understood. Through plant growth experiment, coupled with gas and liquid chromatography-mass spectrometry methods, this study examined the effect of the presence of M. sativa on microbial-associated biochemical transformation of petroleum hydrocarbons. The results of this study revealed that the concentration of exudates within the soil matrix is a function of proximity to root surfaces. Similarly, biodegradation was found to correlate with distance from roots, ranging from ≥ 90% within the rhizosphere to < 50% in bulk soil and unplanted control soil. Most importantly, for the first time in a study of an entire petroleum distillate, this study revealed a statistically significant negative correlation between root exudate concentration and residual total petroleum hydrocarbons. While not all the compounds that may influence biodegradation are derived from roots, the results of this study show that the presence of plant can significantly influence biodegradation of hydrocarbon pollutants through such root exudation as organic acids, amino acids, soluble sugars and terpenoids. Therefore, root exudates, including secondary metabolites, offer great prospects for biotechnological applications in the remediation of organic pollutants, including recalcitrant ones.

A Pseudomonas Plant Growth Promoting Rhizobacterium and Arbuscular Mycorrhiza differentially modulate the growth, photosynthetic performance, nutrients allocation, and stress response mechanisms triggered by a mild Zinc and Cadmium stress in tomato

This study aimed to assess the effectiveness of plant growth-promoting rhizobacteria (PGPR; Pseudomonas strain So_08) and arbuscular mycorrhizal fungi (AMF; Rhizoglomus irregulare BEG72 and Funneliformis mosseae BEG234) in mitigating the detrimental effects of cadmium (Cd) and zinc (Zn) stress in tomato plants. Plant biomass, root morphology, leaf relative water content, membrane stability, photosynthetic performance, chlorophyll content, and heavy metals (HMs) accumulation were determined. Furthermore, an ionomic profile was conducted to investigate whether microbial inoculants affected the uptake and allocation of macro- and micronutrients. Metabolomics with pathway analysis of both roots and leaves was performed to unravel the mechanisms underlying the differential responses to HMs stress. The findings revealed that the levels of HMs did not significantly affect plant growth parameters; however, they affected membrane stability, photosynthetic performance, nutrient allocation, and chlorophyll content. Cadmium was mainly accumulated in roots, whilst Zn exhibited accumulation in various plant organs. Our findings demonstrate the beneficial effects of PGPR and AMF in mitigating Cd and Zn stress in tomato plants. The microbial inoculations improved physiological parameters and induced differential accumulation of macro- and micronutrients, modulating nutrient uptake balance. These results provide insights into the mechanisms underlying the plant-microbe interactions and highlight the differential modulation of the biosynthetic pathways of secondary metabolites related to oxidative stress response, membrane lipids stability, and phytohormone crosstalk.

Impact of Chitosan-Based Foliar Application on the Phytochemical Content and the Antioxidant Activity in Hemp (Cannabis sativa L.) Inflorescences

In the present study, the phytochemical content and the antioxidant activity in the inflorescences of the monoecious hemp cultivar Codimono grown in southern Italy were assessed, and their elicitation was induced by foliar spray application of 50 mg/L and 250 mg/L of chitosan (CHT) at three different molecular weights (low, CHT L; medium, CHT M; high CHT H). The analysis of the phytochemical profile confirmed that cannabinoids were the most abundant class (54.2%), followed by flavonoids (40.3%), tocopherols (2.2%), phenolic acids (1.9%), and carotenoids (1.4%). Cannabinoids were represented almost exclusively by cannabidiol, whereas cannabigerol and Δ9-tetrahydrocannabinol were detected at very low levels (the latter was below the legal limit of 0.3%). The most abundant flavonoids were orientin and vitexin, whereas tocopherols were mainly represented by α-tocopherol. The antioxidant activity was found to be positively correlated with flavonoids and tocopherols. Statistical analysis revealed that the CHT treatments significantly affected the phytochemical content and the antioxidant activity of hemp inflorescences. Notably, a significant increase in the total phenolic content (from +36% to +69%), the α-tocopherol (from +45% to +75%) and β+γ-tocopherol (from +35% to +82%) contents, and the ABTS radical scavenging activity (from +12% to +28%) was induced by all the CHT treatments. In addition, treatments with CHT 50 solutions induced an increase in the total flavonoid content (from +12% to +27%), as well as in the vitexin (from +17% to +20%) and orientin (from +20% to +30%) contents. Treatment with CHT 50 L almost always resulted in the greatest increases. Overall, our findings indicated that CHT could be used as a low-cost and environmentally safe elicitor to improve the health benefits and the economic value of hemp inflorescences, thus promoting their employment in the food, pharmaceutical, nutraceutical, and cosmetic supply chains.

Perenniality, more than genotypes, shapes biological and chemical rhizosphere composition of perennial wheat lines

Perennial grains provide various ecosystem services compared to the annual counterparts thanks to their extensive root system and permanent soil cover. However, little is known about the evolution and diversification of perennial grains rhizosphere and its ecological functions over time. In this study, a suite of -OMICSs - metagenomics, enzymomics, metabolomics and lipidomics - was used to compare the rhizosphere environment of four perennial wheat lines at the first and fourth year of growth in comparison with an annual durum wheat cultivar and the parental species Thinopyrum intermedium. We hypothesized that wheat perenniality has a greater role in shaping the rhizobiome composition, biomass, diversity, and activity than plant genotypes because perenniality affects the quality and quantity of C input - mainly root exudates - hence modulating the plant-microbes crosstalk. In support of this hypothesis, the continuous supply of sugars in the rhizosphere along the years created a favorable environment for microbial growth which is reflected in a higher microbial biomass and enzymatic activity. Moreover, modification in the rhizosphere metabolome and lipidome over the years led to changes in the microbial community composition favoring the coexistence of more diverse microbial taxa, increasing plant tolerance to biotic and abiotic stresses. Despite the dominance of the perenniality effect, our data underlined that the OK72 line rhizobiome distinguished from the others by the increase in abundance of Pseudomonas spp., most of which are known as potential beneficial microorganisms, identifying this line as a suitable candidate for the study and selection of new perennial wheat lines.

New Insight into Ornamental Applications of Cannabis: Perspectives and Challenges

The characteristic growth habit, abundant green foliage, and aromatic inflorescences of cannabis provide the plant with an ideal profile as an ornamental plant. However, due to legal barriers, the horticulture industry has yet to consider the ornamental relevance of cannabis. To evaluate its suitability for introduction as a new ornamental species, multifaceted commercial criteria were analyzed. Results indicate that ornamental cannabis would be of high value as a potted-plant or in landscaping. However, the readiness timescale for ornamental cannabis completely depends on its legal status. Then, the potential of cannabis chemotype Ⅴ, which is nearly devoid of phytocannabinoids and psychoactive properties, as the foundation for breeding ornamental traits through mutagenesis, somaclonal variation, and genome editing approaches has been highlighted. Ultimately, legalization and breeding for ornamental utility offers boundless opportunities related to economics and executive business branding.

Metabolomics and lipidomics insight into the effect of different polyamines on tomato plants under non-stress and salinity conditions

Polyamines (PAs) are key signaling molecules involved in plant growth and stress acclimation processes. This work investigated the effect of spermidine, spermine, and putrescine (alone and in a mixture) in tomato plants using a combined metabolomics and lipidomics approach. The experiments were carried out under non-stress and 100 mM NaCl salinity conditions. Shoot and root biomass, as well as SPAD values, were increased by the application of exogenous PAs but with differences across treatments. Similarly, root length density (F: 34, p < 0.001), average root diameter (F: 14, p < 0.001), and very fine roots (0.0-0.5 mm) increased in PA-treated plants, compared to control. Metabolomics and lipidomics indicated that, despite being salinity the hierarchically prevalent factor, the different PA treatments imposed distinct remodeling at the molecular level. Plants treated with putrescine showed the broader modulation of metabolite profile, whereas spermidine and spermine induced a comparatively milder effect. The pathway analysis from differential metabolites indicated a broad and multi-level intricate modulation of several signaling molecules together with stress-related compounds like flavonoids and alkaloids. Concerning signaling processes, the complex crosstalk between phytohormones (mainly abscisic acid, cytokinins, the ethylene precursor, and jasmonates), and the membrane lipids signaling cascade (in particular, sphingolipids as well as ceramides and other glycerophospholipids), was involved in such complex response of tomato to PAs. Interestingly, PA-specific processes could be observed, with peculiar responses under either control or salinity conditions.

Halophytes for phytoremediation of hazardous metal(loid)s: A terse review on metal tolerance, bio-indication and hyperaccumulation

Phytoremediation is a cost-effective and environment friendly method for cleaning metal(loid)s from contaminated soils. Species with exceptionally higher shoot metal concentrations (hyperaccumulators) seem ideal for phytoremediation, though some metal tolerant species with 'above normal' values with higher translocation factor (TF) may also serve the purpose. Halophytes not only remove salts and metalloids from soils but may also be cultivated as non-conventional crops. Nurturing halophytes requires precise understanding of their nature and efficient management for sustainable use. Species with low metal concentrations in their edible parts (especially leaves) may be grown as forage and fodder, but those with metal hyperaccumulation could prove fatal due to their serious health hazards. Like other metallophytes, redundant use of the term 'metal hyperaccumulation' among halophytes needs to be revisited for its ambiguity and potential pitfalls. Similarly, understanding of metal tolerance and shoot accumulation nature of halophytes is needed prior to their use. This review is an attempt to compare halophytes with potential of metal bioindication, phytostabilization and hyperaccumulation (as per definition) as well as their 'obligate' and 'facultative' nature for appropriate uses.

Enhancing rhizoremediation of petroleum hydrocarbons through bioaugmentation with a plant growth-promoting bacterial consortium

The slow rate of natural attenuation of organic pollutants, together with unwanted environmental impacts of traditional remediation strategies, has necessitated the exploration of plant-microbe systems for enhanced bioremediation applications. The identification of microorganisms capable of promoting rhizoremediation through both plant growth-promoting and hydrocarbon-degrading processes is crucial to the success and adoption of plant-based remediation techniques. In this study, through successive enrichments of soil samples from a historic oil-contaminated site in Wietze, Germany, we isolated a plant growth-promoting and hydrocarbon-degrading bacterial consortium dominated by Alphaproteobacteria. In microcosm experiments involving Medicago sativa L. and the isolated bacterial consortium, we examined the ability of the consortium to enhance rhizoremediation of petroleum hydrocarbons. The inoculation of M. sativa with the consortium resulted in 66% increase in plant biomass, and achieved a 91% reduction in diesel fuel hydrocarbon concentrations in the soil within 60 days. Metagenome analysis led to the identification of genes and taxa putatively involved in these processes. The majority of the coding DNA sequences associated with plant growth promotion and hydrocarbon degradation in this study were affiliated to Acidocella aminolytica and Acidobacterium capsulatum indicating their potential for biotechnological applications in the rhizoremediation of sites contaminated by petroleum-derived organic pollutants.

Reduction of Cu and nitrate leaching risk associated with EDDS-enhanced phytoextraction process by exogenous inoculation of plant growth promoting rhizobacteria

Biodegradable chelant (S,S)-N,N'-ethylenediaminedisuccinic acid (EDDS) has the more advantages of enhanced metal mobility, rapid degradation, environmental friendliness, and ammonium release. However, the risk of metal and/or nitrate residues and leaching within EDDS biodegradation remains as the bottleneck for the widespread application of EDDS-induced phytoremediation. This study aims to explore if the inoculation of plant growth-promoting rhizobacteria (PGPRs) can eliminate the risk associated with the short-term application of EDDS by investigating Cu phytoextraction and soil nitrate content. Results showed that EDDS application significantly increased the copper (Cu) concentration in shoots, soil total Cu, NH₄⁺-N and NO₃^--N content, but decreased plant biomass. The inoculation of PGPRs in the soil showed a strong ability to increase plant biomass, Cu phytoextraction and soil NH₄⁺-N content, and decrease soil Cu and NO₃^--N content. Moreover, bacterial dominant taxa were found to be the largest contributors to soil NH₄⁺-N and NO₃^--N variation, and the abundance of denitrifying bacteria (Bacteroidetes and Stenotrophomonas) decreased in the treatment with PGPRs. The risk of residual Cu and nitrate leaching was reduced by the inoculation of PGPRs without significantly changing the stability of the bacterial community. These new findings indicate that the exogenous application of beneficial rhizobacteria can provide an effective strategy to reduce the risk in metal-contaminated soils of chelant-assisted phytoextraction.

Plant Growth-Promoting Bacteria (PGPB) integrated phytotechnology: A sustainable approach for remediation of marginal lands

Land that has little to no utility for agriculture or industry is considered marginal land. This kind of terrain is frequently found on the edge of deserts or other arid regions. The amount of land that can be used for agriculture continues to be constrained by increasing desertification, which is being caused by climate change and the deterioration of agriculturally marginal areas. Plants and associated microorganisms are used to remediate and enhance the soil quality of marginal land. They represent a low-cost and usually long-term solution for restoring soil fertility. Among various phytoremediation processes (viz., phytodegradation, phytoextraction, phytostabilization, phytovolatilization, phytofiltration, phytostimulation, and phytodesalination), the employment of a specific mechanism is determined by the state of the soil, the presence and concentration of contaminants, and the plant species involved. This review focuses on the key economically important plants used for phytoremediation, as well as the challenges to plant growth and phytoremediation capability with emphasis on the advantages and limits of plant growth in marginal land soil. Plant growth-promoting bacteria (PGPB) boost plant development and promote soil bioremediation by secreting a variety of metabolites and hormones, through nitrogen fixation, and by increasing other nutrients' bioavailability through mineral solubilization. This review also emphasizes the role of PGPB under different abiotic stresses, including heavy-metal-contaminated land, high salinity environments, and organic contaminants. In our opinion, the improved soil fertility of marginal lands using PGPB with economically significant plants (e.g., Miscanthus) in dual precession technology will result in the reclamation of general agriculture as well as the restoration of native vegetation.

Cannabis sativa research trends, challenges, and new-age perspectives

Cannabis sativa L. has been one of the oldest medicinal plants cultivated for 10,000 years for several agricultural and industrial applications. However, the plant became controversial owing to some psychoactive components that have adverse effects on human health. In this review, we analyzed the trends in cannabis research for the past two centuries. We discussed the historical transitions of cannabis from the category of herbal medicine to an illicit drug and back to a medicinal product post-legalization. In addition, we address the new-age application of immuno-suppressive and anti-inflammatory extracts for the treatment of COVID-19 inflammation. We further address the influence of the legal aspects of cannabis cultivation for medicinal, pharmaceutical, and biotechnological research. We reviewed the up-to-date cannabis genomic resources and advanced technologies for their potential application in genomic-based cannabis improvement. Overall, this review discusses the diverse aspects of cannabis research developments ranging from traditional use as herbal medicine to the latest potential in COVID-19, legal practices with updated patent status, and current state of art genetic and genomic tools reshaping cannabis biotechnology in modern age agriculture and pharmaceutical industry.

Improvement of Soil Microbial Diversity through Sustainable Agricultural Practices and Its Evaluation by -Omics Approaches: A Perspective for the Environment, Food Quality and Human Safety

Soil is one of the key elements for supporting life on Earth. It delivers multiple ecosystem services, which are provided by soil processes and functions performed by soil biodiversity. In particular, soil microbiome is one of the fundamental components in the sustainment of plant biomass production and plant health. Both targeted and untargeted management of soil microbial communities appear to be promising in the sustainable improvement of food crop yield, its nutritional quality and safety. –Omics approaches, which allow the assessment of microbial phylogenetic diversity and functional information, have increasingly been used in recent years to study changes in soil microbial diversity caused by agronomic practices and environmental factors. The application of these high-throughput technologies to the study of soil microbial diversity, plant health and the quality of derived raw materials will help strengthen the link between soil well-being, food quality, food safety and human health.