Biochar amendment reduced the risk associated with metal uptake and improved metabolite content in medicinal herbs

Abstract

Contaminations of heavy metals such as lead (Pb) and cadmium (Cd) in medicinal plants (MPs) not only restrict their safe consumption due to health hazards but also lower their productivity. Biochar amendments in the soil are supposed to immobilize the toxic metals, improve the soil quality, and agricultural productivity. However, the impact of biochar on growth attributes, metal accumulation, pharmacologically active compounds of MPs, and health risk is less explored. An experiment was performed on three medicinal plants [Bacopa monnieri (L.), Andrographis paniculata (Burmf.) Nees, and Withania somnifera (L.)] grown in a greenhouse in soil co‐contaminated with Pb and Cd (at two concentrations) without and with biochar amendments (2% and 4% application rates). The fractionation of Pb and Cd, plant growth parameters, stress enzymes, photosynthetic capacity, pharmacologically active compounds, nutrient content, uptake and translocation of metals, antioxidant activities, and metabolite content were examined in the three MPs. The accumulation of Pb and Cd varied from 3.25–228 and 1.29–20.2 mg kg−1, respectively, in the three MPs, while it was reduced to 0.08–18 and 0.03–6.05 mg kg−1upon biochar treatments. Plants grown in Pb and Cd co‐contaminated soil had reduced plant biomass (5%–50% depending on the species) compared to control and a deleterious effect on photosynthetic attributes and protein content. However, biochar amendments significantly improved plant biomass (21%–175%), as well as photosynthesis attributes, chlorophyll, and protein contents. Biochar amendments in Pb and Cd co‐contaminated soil significantly reduced the health hazard quotient (HQ) estimated for the consumption of these medicinal herbs grown on metal‐rich soil. An enhancement in secondary metabolite content and antioxidant properties was also observed upon biochar treatments. These multiple beneficial effects of biochar supplementation in Pb and Cd co‐contaminated soil suggested that a biochar amendment is a sustainable approach for the safe cultivation of MPs.

Significance of Arbuscular Mycorrhizal Fungi in Mitigating Abiotic Environmental Stress in Medicinal and Aromatic Plants: A Review

“…These improvements in plant biomass could be due to an increase in NPK availability, the physical, chemical, and biological properties of soils, and increased soil cation exchange capacity and water retention, resulting in better plant growth [ 270 , 271 ]. The addition of biochar allows the immobilization of TEs such as Pb and Cd through various mechanisms including surface complexation, surface precipitation, electrostatic attraction, physical adsorption, and ion exchange, improving soil quality by increasing water retention and nutrient mineralization, and reducing soil bulk density [ 272 ]. Biochar-based amendments can improve plant biomass, stimulate production of pharmaceutically active compounds, including phenolic and flavonoids, consequently increasing antioxidant activities, and could reduce the risk of metal accumulation in the plant [ 272 ].…”

“…The addition of biochar allows the immobilization of TEs such as Pb and Cd through various mechanisms including surface complexation, surface precipitation, electrostatic attraction, physical adsorption, and ion exchange, improving soil quality by increasing water retention and nutrient mineralization, and reducing soil bulk density [ 272 ]. Biochar-based amendments can improve plant biomass, stimulate production of pharmaceutically active compounds, including phenolic and flavonoids, consequently increasing antioxidant activities, and could reduce the risk of metal accumulation in the plant [ 272 ]. Indeed, biochar has been shown to improve the quality of bioactive compounds and the biomass yield of various MAPs, including kalmegh ( Andrographis paniculata ) cultivated under conditions of water stress, and brahmi ( Bacopa monnieri L.), kalmegh, and ashwagandha ( Withania somnifera L.) cultivated on TE-polluted soil [ 272 , 273 ].…”

Biochar, Compost, and Biochar–Compost Blend Applications Modulate Growth, Photosynthesis, Osmolytes, and Antioxidant System of Medicinal Plant Alpinia zerumbet

“…There is increasing interest in soil amendments, such as biochar (BC) and compost (Co) for the sustainable production of high-value medicinal plants and crops (Basak et al, 2021 ; Liu et al, 2021 ; Nigam et al, 2021 ). BC is a recalcitrant, black carbonaceous, porous, and low-density material produced by the pyrolysis of various biological residues, such as crop residue, wood waste, manure, food waste, forest residue, and sewage sludge (Wang et al, 2020 ).…”

“…These antioxidants play a crucial role in mitigating oxidative stress by regulating reactive oxygen species (Hasanuzzaman et al, 2020 ; Zulfiqar et al, 2021 ). The therapeutic properties of medicinal plants depend on these metabolites and antioxidant activity, which can be improved by amending soils with organic materials (Liu et al, 2021 ; Mehdizadeh et al, 2021 ; Nigam et al, 2021 ). BC application to medicinal plants has been reported to affect plant metabolites and the antioxidant system under stress conditions (Liu et al, 2021 ; Nigam et al, 2021 ).…”

“…The therapeutic properties of medicinal plants depend on these metabolites and antioxidant activity, which can be improved by amending soils with organic materials (Liu et al, 2021 ; Mehdizadeh et al, 2021 ; Nigam et al, 2021 ). BC application to medicinal plants has been reported to affect plant metabolites and the antioxidant system under stress conditions (Liu et al, 2021 ; Nigam et al, 2021 ). Similarly, soils amended with compost can influence these traits in medicinal plants (Burducea et al, 2019 ).…”