Combined application of biochar and sulfur alleviates cadmium toxicity in rice by affecting root gene expression and iron plaque accumulation

Sulfur-functionalized biochar: Synthesis, characterization, and utilization for contaminated soil and water remediation-a review

The development of innovative, eco-friendly, and cost-effective adsorbents is crucial for addressing the widespread issue of organic and inorganic pollutants in soil and water. Recent advancements in sulfur reagents-based materials, such as FeS, MoS2, MnS, S0, CS2, Na2S, Na2S2O32-, H2S, S-nZVI, and sulfidated Fe0, have shown potential in enhancing the functional properties and elemental composition of biochar for pollutant removal. This review explores the synthesis and characterization of sulfur reagents/species functionalized biochar (S-biochar), focusing on factors like waste biomass attributes, pyrolysis conditions, reagent adjustments, and experimental parameters. S-biochar is enriched with unique sulfur functional groups (e.g., C-S, -C-S-C, C=S, thiophene, sulfone, sulfate, sulfide, sulfite, elemental S) and various active sites (Fe, Mn, Mo, C, OH, H), which significantly enhance its adsorption efficiency for both organic pollutants (e.g., dyes, antibiotics) and inorganic pollutants (e.g., metal and metalloid ions). The literature analysis reveals that the choice of feedstock, influenced by its lignocellulosic content and xylem structure, critically impacts the effectiveness of pollutant removal in soil and water. Pyrolysis parameters, including temperature (200-600 °C), duration (2-10 h), carbon-to-hydrogen (C:H) and oxygen-to-hydrogen (O:H) ratios in biochar, as well as the biochar-to-sulfur reagent modification ratio, play key roles in determining adsorption performance. Additionally, solution pH (2-8) and temperature (288, 298, and 308 K) affect the efficiency of pollutant removal, though optimal dosages for adsorbents remain inconsistent. The primary removal mechanisms involve physisorption and chemisorption, encompassing adsorption, reduction, degradation, surface complexation, ion exchange, electrostatic interactions, π-π interactions, and hydrogen bonding. This review highlights the need for further research to optimize synthesis protocols and to better understand the long-term stability and optimal dosage of S-biochar for practical environmental applications.

Integrated physio-biochemistry and RNA-seq revealed the mechanism underlying biochar-mediated alleviation of compound heavy metals (Cd, Pb, As) toxicity in cotton

Biochar has been recognised as an efficacious amendment for the remediation of compound heavy metal contamination in soil. However, the molecular mechanism of biochar-mediated tolerance to compound heavy metal toxicity in cotton is unknown. The objective of this research was to investigate the positive impact of biochar (10 g·kg-1) on reducing damage caused by compound heavy metals (Cd, Pb, and As) in cotton (Gossypium hirsutum L.). The results revealed that biochar reduced Cd concentrations by 24.9 % (roots), and decreased Pb concentrations by 37.1 % (roots) and 59.53 % (stems). Biochar maintained ionic homoeostasis by regulating the expression of metal transporter proteins such as ABC, HIPP, NRAMP3, PCR, and ZIP, and genes related to the carbon skeleton and plasma membrane. Biochar also downregulated genes related to photosynthesis, thereby increasing photosynthesis. Biochar re-established redox homoeostasis in cotton by activating signal transduction, which regulated the activity of the enzymes POD, SOD, and CAT activity; and the expression of related genes. This research revealed the molecular mechanism by which biochar confers resistance to the harmful effects of compound heavy metal toxicity in cotton. The application of biochar as a soil amendment to neutralise the toxicity of compound heavy metals is recommended for cash crop production.

An Overview of the Mechanisms through Which Plants Regulate ROS Homeostasis under Cadmium Stress

Cadmium (Cd2+) is a non-essential and highly toxic element to all organic life forms, including plants and humans. In response to Cd stress, plants have evolved multiple protective mechanisms, such as Cd2+ chelation, vesicle sequestration, the regulation of Cd2+ uptake, and enhanced antioxidant defenses. When Cd2+ accumulates in plants to a certain level, it triggers a burst of reactive oxygen species (ROS), leading to chlorosis, growth retardation, and potentially death. To counteract this, plants utilize a complex network of enzymatic and non-enzymatic antioxidant systems to manage ROS and protect cells from oxidative damage. This review systematically summarizes how various elements, including nitrogen, phosphorus, calcium, iron, and zinc, as well as phytohormones such as abscisic acid, auxin, brassinosteroids, and ethylene, and signaling molecules like nitric oxide, hydrogen peroxide, and hydrogen sulfide, regulate the antioxidant system under Cd stress. Furthermore, it explores the mechanisms by which exogenous regulators can enhance the antioxidant capacity and mitigate Cd toxicity.

Biochar decreases cadmium uptake in indica and japonica rice (Oryza sativa L.): Roles of soil properties, iron plaque, cadmium transporter genes and rhizobacteria

Biochar is an effective and economical strategy for in situ soil cadmium (Cd) remediation. It is essential to comprehensively investigate how biochar mitigates Cd uptake of the main rice subspecies. A pot experiment was established via adding corn stalk biochar into Cd-contaminated soil growing indica Yangdao 6 (YD) and japonica Nangeng 9108 (9108). 9108 had lower shoot biomass (-17.9%) but higher root biomass (+14.4%) and shoot Cd concentration (+29.4%) than YD. Biochar decreased soil available Cd by 25.2% and shoot Cd concentration by 13.6% through the liming and passivation effects. Biochar also favored Cd mitigation by recruiting Fe reducer, Cd remover and plant growth-promoting rhizobacteria (e.g. Bacteroides, Deferrisomatota, Bacillus and Allorhizobium). Besides, biochar reduced Cd uptake by stimulating iron plaques formation for 9108. Moreover, biochar did not reduce Cd uptake by inhibiting Cd transporter genes' expressions and it increased OsHMA2 expression in YD. In conclusion, biochar had great capacity in mitigating Cd pollution and rice subspecies responded differently to biochar in iron plaque formation and Cd transporter genes. The research established a comprehensive understanding of the mechanisms underlying Cd mitigation by biochar and helped to breed low Cd-accumulated rice cultivars to safeguard rice production.

The rhizosphere microbiome reduces the uptake of arsenic and tungsten by Blechnum orientale by increasing nutrient cycling in historical tungsten mining area soils

The growth of pioneer plants in metal mining area soil is closely related to their minimal uptake of toxic elements. Pioneer plants can inhibit the uptake of toxic elements by increasing nutrient uptake. However, few studies have focused on the mechanisms by which the rhizosphere microbiome affect nutrient cycling and their impact on the uptake of toxic elements by pioneer plants. In this study, we selected Blechnum orientale to investigate the potential roles of the rhizosphere microbiome in nutrient cycling and plant growth in a historical tungsten (W) mining area. Our results showed that while the arsenic (As) and W contents in the soil were relatively high, the enrichment levels of As and W in the B. orientale were relatively low. Furthermore, we found that the As and W contents in plants were significantly negatively correlated with soil nutrients (S, P and Mo), suggesting that elevated levels of these soil nutrients could inhibit As and W uptake by B. orientale. Importantly, we found that these nutrients were also identified as the most important factors shaping rhizosphere microbial attributes, including microbial diversity, ecological clusters, and keystone OTUs. Moreover, the genera, keystone taxa and microbial functional genes enriched in the rhizosphere soils from mining areas played a key role in nutrient (S, P and Mo) bioavailability, which could further increase the nutrient uptake by B. orientale. Taken together, our results suggest that rhizosphere microorganisms can improve pioneer plant growth by inhibiting toxic element accumulation via the increase in nutrient cycling in former W mining areas.

Chicken manure-derived biochar enhanced the potential of Comamonas testosteroni ZG2 to remediate Cd contaminated soil

The combined remediation of Cd-contaminated soil using biochar and microorganisms has a good application value. In this study, the effect of chicken manure-derived biochar on CdCO3 precipitation induced by Comamonas testosteroni ZG2 was investigated. The results showed that biochar could be used as the carrier of strain ZG2, enhance the resistance of strain ZG2 to Cd, and reduce the toxicity of Cd to bacterial cells. Cd adsorbed by biochar could be induced by strain ZG2 to form CdCO3 precipitation. Strain ZG2 could also induce CdCO3 precipitation when biochar was added during precipitation formation and fermentation broth formation. The CdCO3 precipitation could enter the pores of the biochar and attach to the surface of the biochar. The single and combined effects of strain ZG2 and biochar could realize the remediation of Cd-contaminated soil to a certain extent. The overall effect was in the order of strain ZG2 with biochar > biochar > strain ZG2. The combination of strain ZG2 and biochar reduced soil available Cd by 48.2%, the aboveground biomass of pakchoi increased by 72.1%, and the aboveground Cd content decreased by 73.3%. At the same time, it promoted the growth and development of the root system and improved the microbial community structure of the rhizosphere soil. The results indicated that chicken manure-derived biochar could enhance the stability of CdCO3 precipitation induced by strain ZG2, and strain ZG2 combined with biochar could achieve a more stable remediation effect on Cd-contaminated soil.