" Assessing the impact of biochar on microbes in acidic soils: Alleviating the toxicity of aluminum and acidity"

Biochar amendment modulate microbial community assembly to mitigate saline-alkaline stress across soil depths

While microbial community assembly in saline-alkali topsoils is well-documented, distribution patterns across biochar application depths and soil layers remain unclear. This incubation study evaluated five treatment: no biochar (CK), homogeneous application (EB), and concentrated applications in upper (FB: 0-10 cm), middle (MB: 10-20 cm), or bottom layers (DB: 20-30 cm). Biochar application significantly accelerated vertical salt migration, with FB inducing 45.55 % and 61.01 % increases in water-soluble Na+ and Cl- accumulation in the bottom layer. Microbial network complexity and interspecies interactions were highest in the upper layer (edges: 926), contrasting sharply with simplified communities in deeper layer (edges ≤552). Community assembly across layers was primarily driven by salt gradients, with deep-layer communities dominated by salt-tolerant taxa (such as Halomonas and Desulfobacterota). Among treatments, FB led to the highest biomarker abundance and α-diversity. Mechanistically, FB mitigated microbial diversity loss in mid-deep layers by establishing a symbiotic consortium of salt-tolerant keystone taxa (Bacillus-Pseudomonas-Ascomycota), which enhanced stress resilience via cross-feeding. These findings demonstrate that stratified biochar application (FB) optimizes salt redistribution while fostering stress-adapted microbial consortia across soil profiles, offering a targeted strategy for saline-alkali soil remediation.

Biochar for ameliorating soil fertility and microbial diversity: From production to action of the black gold

This article evaluated different production strategies, characteristics, and applications of biochar for ameliorating soil fertility and microbial diversity. The biochar production techniques are evolving, indicating that newer methods (including hydrothermal and retort carbonization) operate with minimum temperatures, yet resulting in high yields with significant improvements in different properties, including heating value, oxygen functionality, and carbon content, compared to the traditional methods. It has been found that the temperature, feedstock type, and moisture content play critical roles in the fabrication process. The alkaline nature of biochar is attributed to surface functional groups and addresses soil acidity issues. The porous structure and oxygen-containing functional groups contribute to soil microbial adhesion, affecting soil health and nutrient availability, improving plant root morphology, photosynthetic pigments, enzyme activities, and growth even under salinity stress conditions. The review underscores the potential of biochar to address diverse agricultural challenges, emphasizing the need for further research and application-specific considerations.

Soil microbiological assessment on diversified annual cropping systems in China

Recent studies have demonstrated that monocropping of flue-cured tobacco can lead to various issues, including nutrient deficiencies, accumulation of allelopathic substances, and disturbance in soil microbial flora. While diversification in cropping systems has proven effective in alleviating monocropping barriers, however, further exploration is needed to understand the potential microbial mechanisms involved in this process. In our study, we set five cropping systems (RR: rice monocropping; TR: tobacco-rice rotation over 20 years; TRA: tobacco-rice-astragalus rotation; TRW: tobacco-rice-wheat rotation; TRO: tobacco-rice-oilseed rape rotation) to explore the impact on crop yield and quality, soil chemical properties, and microbial diversity. The results showed that the yield and gross margin were significantly decreased. Following diversification in cropping systems, particularly after implementing the TRA treatment, the yield and gross margin increased by 27.35% and 38.67%, respectively, compared to the TR treatment. Additionally, the presence of tobacco in the soil resulted in acidification, reduced soil fertility, and suppression of soil microorganism diversity and metabolite abundance. With diversification in cropping systems, there was an increase in soil pH, carbon and nitrogen cycle enzyme activities, and the relative abundance of beneficial microorganisms (acidobacteria, nitrospirillum, and ascomycota) and soil metabolites. Diversification in cropping systems has the potential to increase crop biomass, soil fertility, and soil microbial environment. Our results suggest a scientific foundation for implementing effective nutrient management practices and rational crop rotation systems.

Dynamics of major plant nutrients and enzymatic activities in soil influenced by application of biochar and organic waste

The concentration of salt ions influences the availability and plant nutrients dynamics in the soil. Proper management of these ions can enhance food grain production, helping to feed the growing population. In this experiment, nine fertility combinations were followed to enhance the soil organic carbon and reduce the salt toxicity and monitor the plant nutrient availability. An incubation experiment was conducted for the period of one year with different organic soil amendments in combinations including biochar (BC), pressmud (PM), and farm yard manure (FYM) as follow: T1-control, T2-RDF, T3-FYM (10 t/ha), T4-PM (10 t/ha), T5-BC (10 t/ha), T6-FYM (5 t/ha) + PM (5 t/ha), T7-FYM (5 t/ha) + BC (5 t/ha), T8-PM (5 t/ha) + BC (5 t/ha), T9-FYM (5 t/ha) + BC (2.5 t/ha) + PM (2.5 t/ha). Results showed that addition of organic substance (10 t/ha) significantly (p < 0.05) affected soil pH and electric conductivity. Plant nutrient availability (N, K, and S) was also influenced by application of organic substance (10 t/ha). Organic C and available N were recorded the highest in the treatment T7 (FYM-5 t/ha + BC -5 t/ha); whereas, the highest available K and S were observed in treatment T5 (BC-10 t/ha). The microbial soil fertility indicators (alkaline phosphatases, arylsulphatase, dehydrogenase activity and microbial biomass carbon) were measured the highest in FYM (5 t/ha) + BC (5 t/ha) applied treatment. In conclusion, application of organic substance 10 t/ha (biochar alone or with FYM) improved the plant nutrient availability and soil microbial activities in saline soil. It could be a suitable option for enhancing the soil fertility in saline soils.

Heavy metal immobilization and radish growth improvement using Ca(OH)2-treated cypress biochar in contaminated soil

Heavy metal contamination poses a significant threat to soil quality, plant growth, and food safety, and directly affects multiple UN SDGs. Addressing this issue and offering a remediation solution are vital for human health. One effective approach for immobilizing heavy metals involves impregnating cypress chips with calcium hydroxide (Ca(OH)2) to enhance the chemical adsorption capacity of the resulting woody charcoal. In the present study, un-treated cypress biochar (UCBC) and calcium-treated cypress biochar (TCBC), were introduced into pristine and contaminated soil, at rates of 3, 6, and 9% (w/w). Both BCs were alkaline (UCBC pH: 8.9, TCBC pH: 9.7) with high specific surface area, which improved the soil properties (pH, EC, and OM). Radish (Raphanus sativus) cultivated in pots revealed that both UCBC and TCBC demonstrated significant improvements in growth attributes and heavy metal immobilization compared to the control, with TCBC exhibiting superior effects. The TCBC surface showed highly active nanosized precipitated calcium carbonate particles that were active in immobilizing heavy metals. The application of TCBC at a rate of 9% resulted in a substantial reduction in Zn and Cu uptake by radish roots and shoots. In contaminated soil, Zn uptake by radish roots decreased by 55% (68.3-31.0 mg kg-1), and shoots by 37% (49.3-31.0 mg kg-1); Cu uptake decreased by 40% (38.6-23.2 mg kg-1) in roots and 39% (58.2-35.2 mg kg-1) in shoots. Uptake of Pb was undetectable after TCBC application. Principal component analysis (PCA) highlighted the potential of TCBC over UCBC in reducing heavy metal concentrations and promoting radish growth. Future research should consider the long-term effects and microbial interactions of TCBC application.

Effects of Biochar and Straw Amendment on Soil Fertility and Microbial Communities in Paddy Soils

Straw and biochar, two commonly used soil amendments, have been shown to enhance soil fertility and the composition of microbial communities. To compare the effects of straw and biochar on soil fertility, particularly focusing on soil dissolved organic matter (DOM) components, and the physiochemical properties of soil and microbial communities, a combination of high-throughput sequencing and three-dimensional fluorescence mapping technology was employed. In our study, we set up four treatments, i.e., without biochar and straw (B0S0); biochar only (B1S0); straw returning only (B0S1); and biochar and straw (B1S1). Our results demonstrate that soil organic matter (SOM), available nitrogen (AN), and available potassium (AK) were increased by 34.71%, 22.96%, and 61.68%, respectively, under the B1S1 treatment compared to the B0S0 treatment. In addition, microbial carbon (MBC), dissolved organic carbon (DOC), and particulate organic carbon (POC) were significantly increased with the B1S1 treatment, by 55.13%, 15.59%, and 125.46%, respectively. The results also show an enhancement in microbial diversity, the composition of microbial communities, and the degree of soil humification with the application of biochar and straw. Moreover, by comparing the differences in soil fertility, DOM components, and other indicators under different treatments, the combined treatments of biochar and straw had a more significant positive impact on paddy soil fertility compared to biochar. In conclusion, our study revealed the combination of straw incorporation and biochar application has significant impacts and is considered an effective approach to improving soil fertility.

The potential and prospects of modified biochar for comprehensive management of salt-affected soils and plants: A critical review

Soil salinization has become a global problem that threatens farmland health and restricts crop production. Salt-affected soils seriously restrict the development of agricultural, mainly because of sodium ion (Na+) toxicity, nutrient deficiency, and structural changes in the soil. Biochar is a carbon (C)-based substance produced by heating typical biomass waste at high temperatures in anaerobic circumstances. It has high cation exchange capacity (CEC), adsorption capacity, and C content, which is often used as a soil amendment. Biochar generally reduces the concentration of Na+ in soil colloids through its strong adsorption, or uses the calcium (Ca) or magnesium (Mg) rich on its surface to exchange sodium ions (Ex-Na) from soil colloids through cation exchange to accelerate salt leaching during irrigation. Nowadays, biochar is widely used for acidic soils improvement due to its alkaline properties. Although the fact that biochar has gained increasing attention for its significant role in saline alkali soil remediation, there is currently a lack of systematic research on biochar improvers and their potential mechanisms for identifying physical, chemical, and biological indicators of soil eco-environment assessment and plant growth conditions affected by salt stress. This paper reviews the preparation, modification, and activation of biochar, the effects of biochar and its combination with beneficial salt-tolerant strains on salt-affected soils and plant growth. Finally, the limitations, benefits, and future needs of biochar-based soil health assessment technology in salt-affected soils and plant were discussed. This article elaborates on the future opportunities and challenges of biochar in the treatment of saline land, and a green method was provided for the integrate control to salt-affected soils.

Harnessing the power of exogenous factors to enhance plant resistance to aluminum toxicity; a critical review

Aluminum (Al) is the most prevalent element in the earth crust and is toxic to plants in acidic soils. However, plants can address Al toxicity through external exclusion (which prevents Al from entering roots) and internal detoxification (which counterbalances the toxic-Al absorbed by roots). Nowadays, certain categories of exogenously added regulatory factors (EARF), such as nutritional elements, organic acids, amino acids, phytohormones, or biochar, etc. play a critical role in reducing the bioavailability/toxicity of Al in plants. Numerous studies suggest that regulating factors against Al toxicity mediate the expression of Al-responsive genes and transcription factors, thereby regulating the secretion of organic acids, alkalizing rhizosphere pH, modulating cell wall (CW) modifications, improving antioxidant defense systems, and promoting the compartmentalization of non-toxic Al within intracellular. This review primarily discusses recent and older published papers to demonstrate the basic concepts of Al phytotoxicity. Furthermore, we provide a comprehensive explanation of the crucial roles of EARF-induced responses against Al toxicity in plants. This information may serve as a foundation for improving plant resistance to Al and enhancing the growth of susceptible species in acidic soils. And this review holds significant theoretical significance for EARF to improve the quality of acidic soils cultivated land, increase crop yield and quality, and ensure food security.