Biochar and microbial inoculants as natural agents with beneficial potential for soil health and plant growth

1 Introduction

Biochar, a carbonaceous material, is increasingly used for the remediation of anthropogenically affected soils to restore their ecological functions and improve physico-chemical properties (Getahun et al., 2020). Biochar, produced by pyrolyzing woody biomass, crop residues, animal wastes and sewage sludge, is emerging as an important soil amendment in sustainable agriculture (Bolan et al., 2023). During pyrolysis, organic materials are converted into biochar, non-condensable syngas and condensable liquid fractions under low-oxygen or anoxic conditions (Afshar and Mofatteh, 2024). Biochar is a solid carbon-rich material characterized by a large specific surface area, which enables it to retain water and nutrients and gradually make them available to plants and soil microorganisms (Kamyab et al., 2025). Owing to its porous structure, reactive surface functional groups and relatively inert carbon framework, biochar is widely applied in agriculture and ecological restoration to modify soil pH, supply labile carbon, increase micro-habitat heterogeneity and enhance crucial soil properties such as aeration, nutrient availability and the root–soil interface (Zaid et al., 2024). These changes, in turn, influence microbiota assembly and activity and support the growth of beneficial plants, including those used for phytoremediation (Zhao et al., 2024; Yasin et al., 2024). Recent studies and meta-analyses further confirm that biochar can significantly alter soil microbial abundance, enzyme activities and nutrient cycling, reinforcing its central role in soil-microbe interactions.

Soil microbial diversity plays a central role in terrestrial biogeochemical cycling, disease suppression and ecosystem resilience (Li et al., 2026). However, shifts in microbial community structure in response to biochar are strongly modulated by the soil physicochemical background, local climate and hydrology, and the method and rate of biochar application (Hu et al., 2024). Biochar inputs alter the quantity and quality of resources and habitat structure in soil, which differentially affect these environmental drivers and help explain the diversity patterns reported across soil types and climatic conditions (Table 1) (Li et al., 2026). An important property of biochar in this context is its hierarchical pore structure: micro (<2 µm), meso (2–50 µm) and macro (>50 µm) pores, which provide protected micro-habitats for beneficial microbiota (Gorovtsov et al., 2020). Low-molecular-weight hydrocarbons on biochar surfaces may be utilized by soil microbes as carbon sources and can also act as signaling molecules that stimulate or inhibit microbial activity and plant growth (Xu et al., 2025a). In addition to biochar’s intrinsic characteristics, soil type can markedly affect the rate and extent of microbial colonization (Zhang et al., 2023a). Freshly applied biochar may also release organic substances into the soil that support microbial growth and further promote colonization (Wu et al., 2025).

Table 1. Diverse role of biochar application in soil and plant system.

Microbial inoculants comprising plant growth-promoting microorganisms (PGPM) isolated from diverse environments offer a cost-effective, environmentally benign and promising strategy to enhance crop yields while mitigating soil and plant-related stresses (Ansabayeva et al., 2025). Beneficial microbes support host plants through both direct and indirect mechanisms (Shahwar et al., 2023). Direct mechanisms include biological nitrogen fixation, phosphorus solubilization, siderophore production, phytohormone synthesis and reduction in ethylene levels via ACC deaminase activity (Timofeeva et al., 2023). Indirect mechanisms involve the production of antibiotics, iron chelation, synthesis of exopolysaccharides and secretion of antifungal metabolites such as chitinases (Chen et al., 2024a). Collectively, these mechanisms ultimately enhance major physiological processes in plants, such as protein synthesis, photosynthesis, lipid metabolism and respiration (Sohaib et al., 2020). Although microbial inoculants are generally suitable and easy to use for crop improvement, under field conditions, the performance of single-strain inoculants is often inconsistent due to their limited adaptability under variable environmental conditions (Díaz-Rodríguez et al., 2025).

It has been reported that the adaptability and field performance of bacterial inoculants can be improved by deploying microbial consortia (mixed inoculants composed of multiple microbes) (Xu et al., 2025b). Multiple strains tend to perform better in diverse soils because different microbes require different pH, temperature and moisture ranges for effective root colonization, resistance against phytopathogens, metabolic activities, nitrogen fixation, hormone and antibiotic production and phosphorus solubilization (Table 2) (Liu et al., 2023). Therefore, the use of microbial consortia provides a broad spectrum of beneficial functions without recourse to genetic engineering, making multi-strain inoculants a more reliable approach for crop yield enhancement. However, selecting compatible strains and formulating stable consortia is time-consuming and technically challenging. Moreover, the application of microbial inoculants under natural field conditions may sometimes fail to enhance crop growth because of diverse environmental constraints and consequently, the adoption of biofertilizers by farmers remains lower than that of conventional agrochemical inputs.

Table 2. Role of microbial inoculants in promotion of plant and soil health.

Microbial colonization on biochar surfaces has been widely studied, yet a general conclusion regarding the underlying chemical and physical processes remains elusive because of the wide diversity of feedstocks, pyrolysis conditions and microbial taxa involved (Gorovtsov et al., 2020). From a material science perspective, surface roughness and topography, surface free energy, surface charge and hydrophobicity are important parameters governing microbial attachment (Gorovtsov et al., 2020). It is often proposed that microbes attach more rapidly to hydrophobic, non-polar surfaces than to hydrophilic ones. Microbe-substrate interactions trigger multiple adaptive responses, including the formation of surface structures such as flagella, pili and fimbriae (Kimkes and Heinemann, 2020). These adaptations can alter the hydrophobicity of the cell wall and membrane, as well as the cell surface charge and can modulate the production of extracellular polymeric substances. Together, these mechanisms enhance cell adhesion to biochar surfaces. In turn, the interaction of beneficial microbiota with biochar can generate synergistic effects on soil processes and plant growth (Gorovtsov et al., 2020). Nevertheless, the mechanisms governing the tripartite interactions among biochar, soil organic/inorganic particles and microbes are not yet fully resolved and a widely accepted unifying mechanism of biochar and soil microbiome effects on soil properties is still lacking. Moreover, there are several reviews published on the sole application of biochar and microbes in agricultural systems (Schmidt et al., 2021; Elnahal et al., 2022; Singh et al., 2022b; Arshad et al., 2024; Khan et al., 2024a; Biswal and Balasubramanian, 2025; Sun et al., 2026), but there is a lack of literature that highlights the combined role of biochar and nano-biochar with microbes to enhance soil properties. Against this backdrop, the present review focuses on the mechanisms of interaction between biochar/nano biochar and microorganisms and their combined effects on soil properties and crop performance under climate-induced stresses.

2 Methodology used in literature search

A comprehensive literature search was conducted to identify relevant studies on biochar-microbe interactions in soil systems using major online databases, including Web of Science, Scopus, PubMed, ScienceDirect and Google Scholar, covering publications from 2010 to 2026. The search employed combinations of keywords related to this study, including biochar, beneficial microbes, soil health, nano biochar, plant stress, soil microbes, etc. Peer-reviewed articles (284) published addressing biochar-microbe interactions in relation to soil health, nutrient cycling, bioremediation, biotic and abiotic stress were included, while conference abstracts, editorials, duplicate records and studies lacking sufficient methodological detail were excluded. All retrieved records were compiled and screened in three stages: title, abstract and full-text evaluation. Relevant data, including biochar characteristics, microbial taxa, soil types and observed functional outcomes, were systematically extracted and synthesized into thematic categories and included in this review (Figure 1).

3 Nano-biochar and nano-bioinoculants for sustainable agriculture

3.1 Nano-biochar: emerging applications

Recent advancements in nanotechnology have improved the properties of conventional biochar with the development of nano-biochar, a nanoscale carbonaceous material having better physicochemical properties. Earlier studies show that nano-biochar is generally prepared by pyrolysis or hydrothermal carbonization of biomass, followed by size reduction techniques like ball milling, sonication, or other top-down approaches (Zhang, 2025). Among all these methods, ball milling is the best because it reduces the particle size as well as increases the surface area, the presence of oxygen-containing functional groups and the number of adsorption sites, which make the material more reactive (Nan et al., 2024). It has also been found that pretreatment and milling processes enhance the reactive surfaces of biochar to produce highly functionalized nanomaterials suitable for environmental and agricultural applications (Nosratabad et al., 2024). The enhanced performance of nano-biochar relates to its surface chemistry and structural modification. It has high porosity, a large specific surface area, greater surface energy and more carboxyl, hydroxyl and carbonyl functional groups than bulk biochar (Chandran and Julie, 2026). These features strengthen electrostatic attraction, ion exchange, surface complexation and redox reactions so that it can interact more effectively with nutrients and contaminants (Salem, 2026). Furthermore, surface functionalization via oxidation, amination, sulfonation and metal impregnation has created more active sites on the surface of nano-biochar and increased its sorption efficiency (Bhandari et al., 2023). Several recent studies have proven that nano-biochar has better adsorption and contaminant immobilization than conventional biochar. Iron oxide-modified nano-biochar was reported to remove over 90% of arsenic by Nath et al. (2019), while Li et al. (2020a) found high adsorption of tetracycline and Hg (II) with magnetic nano-biochar. El-Fattah et al. (2025) showed effective Cd²⁺ removal through adsorption and surface complexation. These results prove that the higher density of reactive functional groups and nanoscale pores improves the immobilization of heavy metals and organic pollutants. Moreover, studies are being carried out on nano-biochar for the retention and delivery of nutrients. Khan et al. (2025) observed that formulations of nano-biochar allow for the slow release of essential nutrients in such a way that nutrient-use efficiency is enhanced while losses are minimized (Shafiq et al., 2023). Recent studies have focused on nano-biochar as a multi-functional amendment that enhances nutrient cycling, reduces the bioavailability of contaminants, improves soil quality and promotes sustainable agriculture (Bhandari et al., 2023; Salem, 2026).

3.2 Nano-enabled microbial formulations and nano carriers for their effective delivery

Nano formulations of microbial inoculants address some of the conventional biofertilizers’ drawbacks, such as poor shelf life and low survival under stress. Recent studies have shown that nano-bioinoculants improve microbial delivery by shielding the beneficial microorganisms from desiccation, UV radiation, temperature shifts and competition from native microbes (Khalid et al., 2019). Thus, these formulations qualify as promising tools for the enhancement of PGPM in sustainable agriculture (Shah et al., 2025). On the other hand, a major improvement in this area has been the use of nanocarriers for microbial delivery (Garg et al., 2023). Nanomaterials such as chitosan, alginate, silica, hydroxyapatite and biodegradable polymers have been reported to effectively carry PGPM, nitrogen-fixing bacteria, phosphate-solubilizing microbes and arbuscular mycorrhizal fungi (Sultan et al., 2024; Fazelian and Yousefzadi, 2022). These carriers provide a protective microenvironment that can sustain the viability of the microbes both during storage and after application. In a study by Zaman et al. (2025), it was reported that engineered nanocarriers would enable targeted and controlled release of microbial inoculants, ensuring that microorganisms reach the rhizosphere at optimum concentrations for better establishment around plant roots. Chitosan-alginate nano-capsules, polymeric nanoparticles and nano-hydrogels are some of the prominent matrices for encapsulating beneficial microorganisms (Sultan et al., 2026). Hamed et al. (2024) worked on nano-biofertilizer capsules, which were prepared with Pseudomonas fluorescens and nanoscale NPK nutrients; they used chitosan and alginate cross-linked with humic acid. This formulation was designed to protect the microbes and allow gradual release of nutrients and microbial cells into the soil. Other nano-polymer-based encapsulation systems that have reduced microbial mortality and increased the persistence of the inoculant during storage and transport (Sharma et al., 2026). Nano-enabled formulations improve survival and rapid population declines are generally observed due to environmental stress and nutrient limitations in the case of most traditional biofertilizers (Singh et al., 2025a). The microorganisms are encapsulated within a protective matrix provided by the nano-formulation, thereby minimizing stress on the microorganisms and increasing adaptation to the soil environment (Sharma et al., 2025). Studies have shown that nano-encapsulated microorganisms maintain higher viability and metabolic activity compared to their non-encapsulated counterparts, leading to better root colonization and enhanced plant growth-promoting activity (Cloete, 2025; Raghuvanshi et al., 2026). The nanocarriers are reservoirs that release nutrients and microbial metabolites gradually under the influence of environmental conditions. This will enhance nutrient-use efficiency by reducing losses through leaching (Otaiku et al., 2022). Therefore, nano-carriers would be considered an advanced approach in the next generation for delivering beneficial microorganisms more precisely and effectively in sustainable agriculture.

3.3 Future potential of nano-biochar-microbial systems

The future development of nano-biochar-microbial systems is aimed at creating integrated platforms that would enhance microbial delivery, nutrient efficiency, contaminant remediation and plant stress tolerance (Figure 2). It was revealed in a study that the nanoscale properties of biochar make it possible to design microbial carriers with better stability and functionality (Chen et al., 2022). Microbial cells attached to the surfaces of nano-biochar remain shielded from various environmental stresses such as desiccation, UV radiation, sudden changes in temperature and scarcity of nutrients (Hamed et al., 2024). This protection may enhance the survival of the microbes after being applied to the soil and consequently support beneficial populations around the plant root (Wang et al., 2022). Other studies have shown that carriers based on biochar improve microbial colonization, increase enzymatic activities and enhance nutrient cycling in the rhizosphere to promote plant growth under adverse conditions (Zaman et al., 2025). Researchers are focused on smart nano-enabled formulations for the slow release of nutrients and microbial control. Nano-biochar particles have the capacity to adsorb nutrients and microbial metabolites and later release them based on environmental conditions (Li et al., 2020). This will synchronize the availability of nutrients with the demand by plants and will help to maintain an active microbial population in the root zone (Shah et al., 2025). Such systems may enhance nitrogen efficiency, availability of phosphorus and acquisition of micronutrients while minimizing losses of nutrients through leaching and volatilization (Garg et al., 2023). The nano-biochar-microbial system is very important in climate-smart agriculture. Heavy metals and contaminants are immobilized by nano-biochar through adsorption and ion exchange. Pollutants are transformed by microorganisms through biosorption and enzymatic detoxification (Ali et al., 2026). This method enhances remediation and restores soil fertility, hence increasing crop productivity in contaminated environments. Involvement of advanced microbial consortia, omics technologies, AI-assisted selection and precision agriculture will expedite the formulation of nano-biochar crop specificity. Long-term field evaluations, environmental risk assessments and regulatory frameworks are required for large-scale adoption in agriculture.

4 Biochar-microbe interaction mechanisms for sustainable agriculture

The use of microbes is an environmentally benign strategy that plays a crucial role in improving plant health and reducing the stress that hampers the yield (Sharma et al., 2020a). In the last few years, a lot of research has focused on beneficial microbes’ habitat and how the microbes interact with the host plant and defend plants against various stresses caused by phytopathogens and environmental factors. Therefore, the plant is no longer seen as an individual but instead as a large entity (plant microbiome or phytobiome) or holobiont in which the plant is associated with various kinds of microorganisms, including fungi, bacteria, microarthropods, viruses, protozoa, nematodes, actinomycetes, archaea and others as well as their environment. This microbial community, which represents a second larger genome associated with plants, provides nutrition, tolerance to abiotic stress, pathogen protection and regulates the host immunity (Trivedi et al., 2020). Microbes vary in numbers and diversity based on species in agricultural soil (Gupta et al., 2022). In recent years, several omics technological advancements have provided an in-depth insight into the taxonomy and functional level diversity of these microbes (Kumar et al., 2021). However, it is still unclear the fewer facts, including understanding of assembly rules, host genotype effects, microbe-microbes interaction and environmental factors that regulate the phytobiome and their functions (Tosi et al., 2020). The engagement of beneficial microbes in agriculture is much needed for uplifting the modern agriculture status in terms of advocation of environment sustainability as well as enhancing production efficacy (Pandey and Saharan, 2025). From the very first day, plants started promoting the rhizospheric microbiota and their roots stretched into primeval soils where they interact with diverse, crowded microbial communities (Choudhary et al., 2022). Regularly, plants engineer their rhizosphere by releasing exudates to interact with beneficial microbes (Sharma et al., 2021). It is also reported that the different plant species are associated with precise and unique microbial groups and this may be due to variances in the chemistry of root exudates and plant nutrition uptake rate (Sharma et al., 2020b). Microbes utilize the carbon released by roots as rhizodeposits and play an important role in the food web (Wasikoyo et al., 2026). Phytopathogenic microorganisms, including fungi, bacteria, nematodes and oomycetes, are major in soil, while beneficial microbes include symbiotics, free-living plant growth-promoting rhizobacteria, associative symbionts, arbuscular mycorrhizal fungi and algae. The microbial diversity and their number depend on the quality and quantity of root exudates along with the physicochemical properties of soil (Nazli et al., 2020; Harindintwali et al., 2020). Microbes protect crops by inhibiting plant pathogens through bioactive substances (Munakata et al., 2022). These include siderophores, hydrogen cyanide and fungal cell wall-degrading enzymes such as chitinase, protease, glucanase and lipase. Each enzyme targets specific fungal cell wall components: chitinase breaks down chitin, protease degrades proteins, lipase disrupts lipids and β-1,3-glucanase attacks cell wall carbohydrates (Shurigin et al., 2024). Microbes also promote plant growth through mechanisms like ammonia and IAA production, siderophore production, Zn solubilization and P solubilization (Shurigin et al., 2024). Phosphate-solubilizing microbes address this by converting insoluble P into plant-accessible forms (Sudewi et al., 2020). Phytohormones from plants and microbes not only boost growth but also mediate host-microbe interactions. Siderophores from plant growth-promoting bacteria improve iron bioavailability to enhance growth and bolster defenses against phytopathogens (Singh et al., 2022b; Zheng et al., 2021). These mechanisms highlight microbes’ role in sustainable agriculture as eco-friendly, environmentally benign and cost-effective alternatives to harmful chemicals (Figure 3; Table 3). Other possible microbe-biochar interactions are discussed in the following sub-sections.

Table 3. Quantitative synthesis of reported effect sizes for biochar-microbial systems across studies.

4.1 Biochar-induced microbial habitat engineering fosters microbial specialization and functional effectiveness

Soil physical and chemical structure modifications induced by biochar significantly influence microbial colonization, activity and functional diversity in soil. The addition of biochar to soils results in a reconceptualization of soil spatial architecture into heterogeneous microenvironments capable of supporting microbial diversity through the creation of diverse microbial niches (Pot et al., 2022). These microsites provide microbes with resilience against environmental stress, such as desiccation and predation and protect against changes in redox state (Roy et al., 2025). By providing a high surface area, interconnected pore network and functional groups in abundance, biochar has the potential to create microenvironments with the capacity to sequester water and nutrients while also establishing oxygen and redox gradients that allow for the cohabitation of functionally independent microbial communities (Gan et al., 2025). Biochar acts as an active ecological scaffold that directs the assembly and activity of microbes in soils, wetlands, wastewaters and composts, not only as an inert additive (Singh et al., 2025). Many of these characteristics are most evident through their functions in remediation-oriented systems. In constructed wetlands and wastewater treatment systems, biochar has been extensively utilized as both a microbial carrier and an adsorbent, providing adsorption capabilities for heavy metals and organic contaminants as well as providing structural habitats for functional microbial populations capable of breaking down these contaminants (Pandey et al., 2025). Because the physical adsorption of contaminants and their biological transformations occur in the same location, biochar systems present an important advantage over traditional single-process systems with respect to contaminant removal efficiency and system stability (Guo et al., 2025). Therefore, while physicochemical properties will play a role in determining biochar’s effectiveness in remediation, its ability to create and maintain active microbial habitats through structuring is the primary factor influencing biochar’s effectiveness in this role.

An important part of ecological engineering is using biochar to enhance organisms’ growth and substrate development through the establishment of biofilms and microbial communities (Bolan et al., 2023). The physical configuration of the biochar’s pore network allows for a sheltered location for bacteria and archaea to adhere, while the chemical characteristics of biochar increase the likelihood of microbial attachment (Kayoumu et al., 2025). The presence of easily degradable forms of carbon in the biochar also provides a readily available energy source for microbial growth and activity and this leads to selective enrichment of functional groups of microorganisms, such as those involved in nutrient cycling and biodegradation (El-Aradi et al., 2026). Several studies demonstrate the positive influence of biochar on microbial abundance and diversity. However, the results are quite variable. Other factors, such as feedstock source, pyrolysis temperature, application rate, soil characteristics and environmental conditions, also lead to different responses from microorganisms, which hinders a universal recommendation on habitat engineering strategies (Yu et al., 2023). However, both the quantity and quality of the biochar-derived carbon will differ based on the particular physical and chemical properties of each biochar, including the temperature of pyrolysis. Biochars have various degrees of structural and chemical characteristics that are determined by their pyrolysis temperatures, having been found to affect their suitability as microbial habitats (Tomczyk et al., 2020). Typically, high-temperature biochars (550–800 °C) have highly-developed microporous structures that may produce micro-anoxic environments and favor denitrification. Low-temperature biochars (400 °C) are generally richer in labile carbon, having downgraded pore network structures; thus, they could create imbalances in microbial population and/or produce incomplete denitrification effects (Antonangelo et al., 2019). The contrasting properties of high and low temperature biochars demonstrate that the quality of a microbial habitat is affected by the carbon species availability and may also be influenced by the interaction of the carbon’s pore structure, surface chemistry and the metabolic requirements of the microorganisms (Ndoung et al., 2021).

The use of molecular techniques to investigate how biochar affects the structure and function of microbial communities has continued to increase. Through high-throughput sequencing and phospholipid fatty acid analysis, researchers have repeatedly shown that biochar increases microbial diversity and changes microbial communities (Kerner et al., 2023). For example, using leaf-based biochar in forests produces greater bacterial diversity compared to using woodchips as a feedstock, highlighting the significance of feedstock-based habitat heterogeneity (Qiu et al., 2023). In addition, higher abundances of specific groups of microorganisms (e.g., Betaproteobacteria, Deltaproteobacteria and Chloroflexi) are associated with increased nutrient transformation and degradation of hydrocarbons over specific ranges of pH (Muhammad et al., 2026b). This implies that while biochar enhances overall microbial quantity, it also leads to a reorganization of the functional capacity of microbial communities (Li et al., 2020). The consequences of the changes made to the habitats discussed above influence biogeochemical cycle rates and the level of how well these systems remove chemical contaminants. Higher numbers of bacteria and fungi have been positively correlated with faster decomposition of carbon and more effective decomposition of environmental pollutants, specifically triazine herbicides and PAHs that are found in contaminated soils (Bala et al., 2022; Agbede et al., 2024). Taken together, the findings from these investigations indicate that habitat modification, through the usage of biochar, fosters microbial specialization and functional effectiveness across many different types of habitats (Gao et al., 2024). These responses to the microbiological structures in the soil provide the framework for biological processes that stabilize soils. When microorganisms are colonized and active in increasing numbers, they produce more extracellular polymeric substances (EPS), develop biofilms and create minerals through biochemical means; all these processes contribute to binding particles, forming aggregates and stabilizing soil structure (Zhang et al., 2024b). Biochar as a habitat engineer links microbiological ecology with the geological/physical processes of soil stabilization, thereby bridging the biological activity of soils with engineering results.

4.2 Biochar-microbes interaction for nutrient and enzymatic regulation

Through its involvement in controlling nutrient dynamics and enzyme activity in soil systems, biochar has a significant impact on microbial metabolism and biogeochemical cycling. The biochar effects result from both direct physicochemical interactions with enzymes and substrates and indirect regulation by the microbial community (Giagnoni and Renella, 2022). Thus, biochar is an important interface between abiotic properties and biological function. Therefore, the effect of biochar on nutrient transformation processes does not occur independently, but rather it is primarily driven by how microbial communities respond to the environmental modifications caused by biochar (DeLuca et al., 2024). The way that biochar modifies enzymatic activity is mainly through its direct binding to exogenous enzymes and their substrates. This direct binding can be attributed to the high surface area and the large number of chemical functional groups present on biochar, which together enable phosphate groups and highly polar reactive groups to grab onto enzyme and substrate molecules (Zeng et al., 2024). These interactions can change the shape of enzymes, making them unusable, or can interfere with the enzyme and substrate coming together, either by blocking substrates from getting to the enzyme or by blocking the active site of the enzyme (Bednik et al., 2023). The specific enzymatic effect of biochar depends on the surface chemistry of biochar, specifically whether the functional groups are reactive or have an aromatic structure that facilitates binding interactions (Rahmanian and Khadem, 2024). Additionally, some of the organic compounds found in residual biochars, such as polycyclic aromatic hydrocarbons (PAHs), benzofurans and heterocyclic compounds, may pollute the enzyme environment, resulting in reduced rates or inhibition of catalytic conversion of substrates by significant enzymes including β-N-acetyl glucosaminidase, leucine aminopeptidase, β-glucosidase and lipase; some residual contaminants may function as allosteric modulators of the enzyme’s catalytic efficiencies (Gupta et al., 2020). The movement of electrons between free radicals on the biochar surface and oxidoreductase reactions affects the enzyme reactions. The chemical reaction between biochar and cells is not limited to physical interactions; chemical interactions also affect enzyme activity, by affecting biochemical processes through oxidation and reduction (Xie et al., 2024). Biochar impacts enzyme activity through a variety of mechanisms, but findings are inconsistent. Some research confirmed that it enhances enzymatic activity by improving microbial habitats and nutrient availability, while other research reported its inhibitory effects due to adsorption of enzymes, limitation of substrates, or residual compounds (Díaz-Rodríguez et al., 2025). These different results indicate that the response of the enzyme depends on the characteristics of the biochar, as well as the properties of the soil and the conditions in the environment.

The regulation of enzymes in biochar-amended environments is primarily influenced by microbial activities. The impact of adding biochar to soil on microbial community composition and activity is strongly related to changes in certain soil physicochemical properties, such as changes in pH, electrical conductivity and availability of nutrients (El-Aradi et al., 2026). The change in soil pH after biochar addition has consistently been positively correlated with an increase in the growth of microorganisms and an increase in their production of nutrient-cycling enzymes (Dai et al., 2021). In addition, microbial activity often decreases as soil conditions become less favorable, which will result in less production of enzymes. Thus, the overall impact of biochar on enzymatic activity is greatly dependent upon the activity of the microorganisms as opposed to their direct chemical reactions with the soil (Hou et al., 2014). There is an intrinsic link between biochar’s impact on the enzymatic activities and the biochar’s functions for nutrient cycling through the major biogeochemical processes. The enzymes that are used as indicators of nutrient transformations are: β-xylosidase and β-D-cellobiosidase for carbon cycling; urease and protease for nitrogen transformations; sulfatase and aryl-sulfatase for sulfur cycling; and phosphomonoesterases for phosphorus turnover (Nourmandipour et al., 2021). The regulation of these enzyme systems directly influences microbial biomass, nutrient availability and soil chemical properties. Importantly, the increased enzymatic activity, along with microbial colonization and attachment to biochar surfaces, supports processes such as microbial cell bridging, flocculation and aggregation; thus, linking nutrient cycling and soil structural stability and contaminant bioremediation (Mukherjee et al., 2022).

In addition to adding nutrients to the soil, the interaction of biochar with soil organics leads to more nutrients being available to microbes (Ali et al., 2025). Biochar amendments have been shown to increase the mineralization of the native organic matter in soil, which increases the amount of carbon available for use by microbes (Chagas et al., 2022). Both of these processes involve microbial activity that leads to the formation of organo-mineral complexes and the stabilization of aggregates in the soil (Lyu and Zimmerman, 2025). Biochar has an extremely variable nutrient composition, which directly impacts how microbes respond to different forms of biochar. During pyrolysis, nitrogen can be lost through volatilization, while phosphorus and potassium levels generally increase as the temperature of pyrolysis rises because less biochar is produced as a result of higher heat. Depending on the conditions of pyrolysis, secondary nutrients like sulfur will either be retained or lost. The degree of nutrient variability affects the microbial metabolism and the efficiency of nutrient cycling associated with biochar; therefore, it is important to determine the optimal parameters for biochar production for selected applications. Also, due to the presence of 60-70% carbon in biochar, it provides a long-term source for carbon sequestration (Ali et al., 2025). Dissolved organic carbon (DOC) from biochar modifies the composition of soil organic matter and aids in the regulation of nutrients that are released into soils via the process known as mineralization and the transport of contaminants through soils (Azeem et al., 2025). Further, through the existence of unpaired electrons on the biochar surface, biochar facilitates biochemical reactions that occur through redox reactions and affects the transformation of organic contaminants (Wu et al., 2025). Thus, the interaction between physicochemical properties of biochar and microbial processes represents an evolving relationship whereby microorganisms are the principal catalysts that convert changes induced by biochar into functional results (Kocsis et al., 2022). This integrative interaction will provide enhanced ecosystem services associated with improved nutrient cycling, increased microbial activity, enhanced soil stability and enhanced environmental sustainability.

4.3 Biochar-microbe mediated soil aggregation and structural stability

Biochar interacts with microbes in three ways: 1. Microbially induced mineral precipitation (MICP) 2. Extracellular polymeric substance (EPS) production 3. Biofilm-mediated aggregation, all three processes help in creating better inter-particle bonding in soils, resulting in a reduction of pore space and an increase in the mechanical strength of soils. Through various metabolic mechanisms like urecolysis, denitrification, sulfate reduction and photosynthesis, microorganisms induce calcification (CaCO₃) by inducing precipitation via the reaction of carbonate ions produced from the metabolic pathways with Ca²⁺, thereby producing calcite at particle contact (Dubey et al., 2025). Bridging calcite between soil particles is formed, which leads to the creation of stable soil aggregates, therefore improving pore architecture, water retention, aeration and root penetration. Such alterations provide conducive circumstances for microbial colonization and nutrient transformation in the rhizosphere, thereby coupling bio-cementation processes with soil health and plant productivity (Pakbaz et al., 2018).

Microbial cells and their exopolysaccharides (EPS) function as nucleation sites for mineral precipitation. Many bacteria have negatively charged surfaces, which attract divalent cations such as calcium (Ca²⁺). Therefore, localized concentration of divalent cations produces supersaturation of the mineral solution and promotes the growth of crystals (Fein et al., 1999). EPS/matrices of bacterial extracellular polymers include all or some combination of polysaccharides, proteins and nucleic acids concentrated by the bacterial cell (Li et al., 2021). Moreover, promotion of nucleation through the concentration of ions and reducing the activation energy barrier required for the precipitation of the mineral, bacterial EPS’s also stimulate the deposition of calcite at the point of contact of particles to create and/or strengthen the interconnection between particles and enhance the transfer of load in the soil matrix (Tastambek et al., 2026). Through the aggregation of soil particles supported by EPS, the cohesion and stability of soil aggregates may be enhanced by 20-40% in the absence of the concurrent precipitation of minerals (Redmile-Gordon et al., 2020). EPS-mediated binding also triggers the creation of biologically active microhabitats that hold moisture, protect microbial communities from environmental stresses and enhance nutrient exchange between microorganisms and plant roots, in addition to aggregate stability (Chagas et al., 2022). EPS generation is therefore essential to maintain the functionality of the rhizosphere and to ensure sustainable crop yield.

Research exhibits that adding biochar to MICP’s increased the amount of CaCO₃ that precipitated compared with just using microbes, with an increase of 15 – 35% causing more uniform cementation and better mechanical properties (Zheng et al., 2022; Ouyang et al., 2023; Priyadarshi and Sharma, 2025). Biochar may function as a mineral nucleation template, facilitating the adsorption of calcium ions and the crystallization of surfaces through the use of carbonyl (COOH) and hydroxyl (OH) functional groups (Mathabatha et al., 2023). In addition to supporting microbial activity, biochar can also modulate the pathways for mineral precipitation, thus improving the effectiveness of bio-cementation (Liu et al., 2024). Such interactions may enhance nutrient cycling activities, including nitrogen transformation and phosphorus mobilization, therefore increasing nutrient availability to plants.

Soils are stabilized by mineral precipitation, the formation of biofilms and the production of EPS, which work together to form strong connections among particles in soils, especially those that contain mostly fine-sized particles, which could result in a lack of mineral precipitation (Joshi et al., 2026; Solanki et al., 2020). In addition to binding soil particles together, EPS enhances the soil’s ability to retain moisture and provide protection to microbial populations from environmental stress, thereby promoting long-term soil stabilization. Together, these biological processes complement the mineral cementation, leading to stronger soil structures (Das et al., 2025). The bio-cementation process and microbes’ ability to bind soil are influenced dramatically by both environmental and operational conditions (Zhang et al., 2024a). If the temperature and/or pH parameters change, there is likely to be an adverse effect on crystal morphology, distribution and bonding, all of which are important for the strength and durability of the soil.

Microbial processes utilizing biochar for bio-cementation can be viewed as a green alternative to using chemical stabilizers and have positive environmental impacts. As a result of bio-cementation, calcium carbonate is produced, which improves the mechanical properties of soils and immobilizes contaminants, thereby decreasing the mobility of heavy metals and the bioavailability of these contaminants (Pansare et al., 2024). In addition, biochar sequesters carbon dioxide and enhances biological activity in soil, thereby greatly contributing to the ecological sustainability of the soil (Adekiya et al., 2026). MICP, EPS production and biofilm formation are the processes through which soil aggregation, nutrient retention and microbial habitats are regulated. These functions, together with biochar, enhance soil stability, rhizosphere function and beneficial microbial activity (El-Aradi et al., 2026). Improved water retention and availability of nutrients with enhanced root growth result in better plant performance and soil health.

4.4 Biochar-microbe mediated soil remediation and functional soil recovery

The integrated approach of using microbes with biochar together in the remediation of contaminated soils or sediments can be considered a feasible method for successfully achieving functional remediation. It is through this synergistic interaction between microbial activity and biochars that contaminants degradation is enhanced and thus ultimately facilitating ecological recovery as evidenced by the linkages between mechanistic interactions and practical applications (Mukherjee et al., 2022). A clear demonstration of synergy can be found in the bioremediation of polycyclic aromatic hydrocarbons (PAHs). Research showed that rice straw biochars inoculated with Mycobacterium gilvum dramatically increased the ability to degrade PAHs in contaminated soils when compared to using either microbes or biochars alone (Xiong et al., 2017). More specifically, phenanthrene removal in the biochar-microbe systems was 62.6% compared to 47.3% for microbes only and virtually none for the biochars alone (Janus et al., 2020). Furthermore, pyrene removal was about 62.1% for the biochar-microbe systems versus 13.5% for the biochars alone, showing that biochars act more as facilitators of microbial degradation than as independent remediation agents (Das and Pandey, 2025). The enhanced ability of the biochars to degrade the PAHs was due to improved mass transfer of the contaminants to the biochar surface, where the microbes degrade the sorbed pollutants, demonstrating a coupled sorption-biodegradation pathway (Song et al., 2021). Biochar-microbe remediation systems are predominantly regulated by mechanistic interactions at the biochar-microbe–contaminant interface. Biochar acts as a sorbent and as a microbial habitat that accumulates pollutants, nutrients and microbial populations inside discrete microsites (Yang et al., 2018). This spatial linkage allows for simultaneous adsorption and biodegradation processes, thereby increasing the effectiveness of pollutant transformation in comparison to each mechanism acting in isolation.

Microbial consortia immobilized in biochar have great potential for remediating contaminated land. Studies demonstrate that biochar can immobilize microbial consortia and degrade pesticide compounds such as metribuzin at a 96% than untreated soils 30% (Zhang et al., 2023b). Additionally, adding organic substrates to biochar increases the degradation rate of PAHs by increasing the availability of DOC to stimulate hydrocarbon-degrading microbes (Bao et al., 2020). The results indicate that biochar does increase the abundance of microbes and also increase the functional expression of degradation pathways, especially when co-amended with an organic substrate (Song et al., 2024). Biochar in combination with microbes to treat or bind contaminants in sediments and water bodies has been demonstrated to stabilize contaminants for long periods and degrade some of the contaminants in place (Jiang et al., 2024). Biochar, as a capping agent on contaminated sediments, limits the migration of the contaminants and also supports the microbes that breakdown the contaminants (Rahmanian and Khadem, 2024). The combination of the immediate immobilization of the contaminants and the more prolonged biodegradation is important in systems where the impurities remain due to their chemical stability and limited access for microbes (Armanu et al., 2025).

The biochar-microbe synergistic systems are capable of addressing all organic pollutants, as well as antibiotics, petroleum hydrocarbons and emerging contaminants. The ability to remove greater than 95% of paraquat from water is an example of the potential of these systems to treat water (Manikandan et al., 2023). Biochar combined with specific microbial strains has been shown to achieve removal rates from 40-90% for antibiotics, further illustrating their versatility (Liu et al., 2025). Additionally, the biochar-microbe systems inhibit the transmission of antibiotic resistance genes within biochar-amended environments by limiting gene transfer between microorganisms (Fang et al., 2025). Rhizoremediation has been established as an innovative area of research combining plants, improvements in microbial activity and biochar to help remove contaminants via plant roots (Min et al., 2025). Rhizo-degradation of petroleum hydrocarbons and persistent organic pollutants has also been significantly increased by combining plant-associated microbes with biochar (Ali et al., 2020; Yaashikaa et al., 2020; Manikandan et al., 2023). Existing data suggest biochar and microbes act together to remediate polluted sites by removing contaminants from soils, improving microorganisms’ ability to degrade contaminants and restoring ecological health to affected sites (Xiang et al., 2022). These remediation techniques use integrated approaches and provide multiple methods of remediating contaminants and restoring degraded soils by increasing microbial diversity, enhancing nutrient cycling and providing greater ecological stability in the environment (Giagnoni and Renella, 2022; Fang et al., 2025). Therefore, biochar-microbes application play a crucial role in contamination degradation and reclamation of polluted soils.

4.5 Role of biochar-microbial inoculants in mitigation of soil abiotic stress

Soil abiotic stresses like drought, salinity, nutrient scarcity, high rainfall, heavy metal toxicity and temperature extremes cause a significant reduction in agricultural productivity and soil functionality. The use of biochar along with microbial inoculants resolves a large-scale solution for improving stress tolerance (Figure 3; Table 4), which improves soil physicochemical properties, increases microbial activity and improves plant growth (Bolan et al., 2023). The ability of microbially inoculated biochar to exhibit significant potential to mitigate salinity stress through forming a more conducive environment for plants. Salinity can negatively impact soil chemistry by increasing electrical conductivity and affecting the overall ionic balance between Na⁺ ions and K⁺ ions (Abbas et al., 2024a). Adding microbially inoculated biochar to the soil significantly improves the ionic balance and the osmotic potential to help plants withstand osmotic stress caused by excessive salinity in the soil (Abbas et al., 2026b; 2026a). Furthermore, utilizing biochar with PGPR will further increase the osmotic adjustment capacity of plants subjected to salinity stress by enhancing the activity of several antioxidant enzymes, which helps mitigate the damaging effects of high salinity on plant health and productivity (Abbas et al., 2024b). Biochar-microbial inoculant systems significantly enhance soil’s ability to retain moisture and allow for greater adaptation by plants through microbially mediated processes (Abo-Elyousr et al., 2022). Biochar’s porosity increases the soil’s ability to retain moisture and benefits plants through microbes, improving root growth and through microbes modulating stress-responsive pathways in plants (Parastesh et al., 2025). Biochar application decreased plant biomass loss due to drought conditions from approximately 50% to 35%, thereby improving the plants’ level of resilience in conditions where moisture was limited. Further combination of biochar and microbial inoculant systems improved these plants’ water-use efficiency and increased photosynthetic activity (Muhammad et al., 2026a). Microbes produce phytohormones such as indole-3-acetic acid (IAA) and abscisic acid (ABA) that play a critical role in regulating plant response to water stress, while biochar creates a stable environment for continued microbial activity (Mathabatha et al., 2023). Biochar–microbial systems are effective under abiotic stress if they have the capacity to adjust soil properties and activities of living organisms. Water retention, ion exchange, nutrient availability and rhizosphere chemistry are properties of biochar, while those of microbial inoculants include effects on phytohormone production, antioxidant responses and nutrient transformations (Upadhyay et al., 2024). These properties make a combination of both biochar and microbes a dynamic duo for the resilience of both soil and the plant, maintaining their physiological functions even under stressful conditions.

Table 4. Biochar-microbial inoculants reducing abiotic stress.

Heavy metal stress can be reduced through the use of biochar and microbial inoculants. Biochar reduces the bioavailability of heavy metals by immobilizing them with adsorption, ion exchange and precipitation. On the other hand, microbial inoculants reduce heavy metal toxicity by transforming them through the processes of biosorption, bioaccumulation and enzymatic reduction (Ghandali et al., 2024). Studies have shown that biochar and microbial inoculant systems enhance plant growth in contaminated soils by improving soil quality and increasing soil microbial activity. For example, the use of metal-tolerant bacteria such as Pseudomonas spp. in biochar-amended soils has decreased cadmium uptake while increasing microbial diversity, thus demonstrating effective detoxification and the recovery of the ecosystem (Dadhich et al., 2025). Together, both microbial inoculants and biochar can work to decrease both temperature and oxidative stresses. Biochar also increase the efficiency of antioxidant enzyme systems in plants, including peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT); these enzymes help to reduce oxidative damage caused by environmental stress (Salehi et al., 2025). Furthermore, the addition of microbial inoculants increases tolerance to environmental stresses and increases the expression of genes that produce resilient plant types that can withstand extreme environmental conditions (Ndoung et al., 2021). Integrating biological regulation of abiotic stressors with mitigation of abiotic stressors is therefore very important. Biochar and microbial inoculants can really help with soil structure improvement and dynamic nutrient availability during stress period (Upadhyay et al., 2024). Biochar increases soil aggregation, aeration and capability for nutrient retention, while inoculating microorganisms into the soil helps with the cycling of all nutrients and contributes to more fertile soil for plant growth when conditions are not favorable (Rathinapriya et al., 2025). Research suggests that adding biochar to the soil increases soil physical properties and increases the availability of nutrients from the soil, both of which are vital to sustain microbial activity and maximize plant productivity, even if they are experiencing stress conditions (Ali et al., 2025). But the level of stress mitigation responses varies widely across research. Inconsistent results are often obtained due to variations in biochar feedstock, pyrolysis temperature, microbial strain selection soil properties and stress severity (Awad et al., 2022). Therefore, favorable responses recorded under one set of environmental variables cannot be globally extended to other agricultural systems.

4.6 Role of biochar and microbial inoculants for improvement of soil physicochemical and biological properties

Biochar can improve the properties of soils when used in conjunction with microbial inoculants. Both biochar and microbial inoculants offer consistent improvements in soil characteristics like pH, nutrient availability and organic matter content (Figure 4; Table 5). Biochar has the ability to increase the pH of acidic soils, thereby supporting microbial survival and enhancing nutrient access (Omokaro et al., 2025). Field experiments have demonstrated that both biochar and PGPR significantly improve the pH and availability of nutrients compared to soil without treatment (Kari et al., 2021). An investigation conducted by (Çığ et al., 2021) discovered that PGPR treated with either biochar or without raised the SOM test results by 42.59 g kg⁻¹, indicating an enhancement of carbon in the soil. These increases occurred due to both the recalcitrant carbon present in biochar and the impact of PGPR on the activities of microorganisms. Combining biochar with microbial inoculants can increase soil organic carbon (SOC) levels by an average of 49% and can also improve soil pH according to the pre-existing conditions, supporting the potential technology to work across a variety of soils (Song et al., 2024). Additionally, the combination improves soil structure, specifically through biochar’s properties and microbial aggregation processes, resulting in greater porosity and aggregation within the soil.

Table 5. Biochar and microbial applications enhancing soil physicochemical and biological properties.

Combined application of biochar and microbial inoculants improve the cycling of nutrients, increase the amount of nutrients available and retain more nutrients over time. Biochar can store nutrients and help prevent nutrients from being lost through leaching. Microbial inoculants help fix nitrogen, solubilize phosphorus and mineralize organic matter (Salehi et al., 2025). Research has shown a substantial increase in alkaline hydrolysable N, soluble P and K availability in soils treated with biochar and microbial inoculants due to the interaction of these two inputs compared to untreated control soils (Zou et al., 2024). In the presence of biochar, the indigenous microbial inoculant used in this study (Azospirillum brasilense and Arthrobacter crystallopoietes) proliferates 1–6 times more than in untreated control soils, resulting in improved nutrient cycling and plant growth associated with these two inputs (Kari et al., 2021). In addition to improving nutrient use efficiency, biochar-initiated microbial systems hold nutrients and facilitate the conversion of these nutrients into plant-available forms via various soil-borne microbes (Bolan et al., 2023). Together, they reduce the dependency on fertilizers and promote a sustainable method of nutrient management. Using biochar and inoculating soils with microbes greatly enhances the biological properties of the soil. The biochar serves as a medium in which microbes can flourish, allowing them to survive longer, to colonize in greater numbers and to become more active, thus increasing all three factors: the biomass, diversity and functional activity of the microbes (Ngaba et al., 2025).

Biochar-microbial inoculant systems increased the abundance of beneficial bacteria by approximately 71.9% and also increased microbial diversity indices, which support a more productive and healthy microbial community structure. The addition of beneficial groups such as Bacillus, Pseudomonas and Streptomyces to biochar-amended soils supports greater soil health and nutrient cycling (Song et al., 2025). The combination of biochar with microbial inoculants enhanced enzymatic activities associated with biological processes in soils. Enzymes involved in the distribution of carbon, N and P in soils, such as dehydrogenase, phosphatase and protease, were improved by the combination of biochar with microbial inoculants and these increases in enzymatic activity​ contribute to improved biochemistry within the soil system (Nourmandipour et al., 2021; Ali et al., 2025). Moreover, there is a strong link between these improvements in enzymatic activity and an increase in microbial metabolic rate, resulting in greater soil fertility. Biochar-microbes applications can improve soil structure by enhancing both aggregation and porosity (Bolan et al., 2023; Salehi et al., 2025). In studies, it has been reported that the application of microbial and biochar treatments can improve aggregation properties in the soil and decrease the bulk density, improving aeration and water retention. These factors are critical to root growth, water infiltration and soil function (Redmile-Gordon et al., 2020; Araujo et al., 2025). These findings highlight the potential role of biochar-microbe treatments to improve soil properties for better crop production.

4.7 Microbes-biochar application to manage soil-borne pathogens

Biochar amendment in the soil improves soil conditions, which harbor beneficial microbes in the soil, ultimately improving plant growth and health. This happens because its high porosity and specific surface area, balancing pH, higher organic carbon content and other enhancements create a favorable environment in soil for microbes and plants (Khan et al., 2024b). The microbial diversity in soil increases, leading to increased interaction and competition between beneficial and harmful microbiota for space and nutrition in the soil. Thus, biochar escalates the growth of beneficial microbiota, which protect the plants from harmful soil-borne microbes (Figure 3; Table 6) (Ilyas et al., 2023). The varied pore size and structure of biochar, viz., micropores, mesopores and macropores, create the appropriate conditions for growth and reproduction of beneficial fungi, arbuscular mycorrhizal fungi and bacteria, which actively colonize the plant roots (Yang et al., 2024). It has also been found that the combined effect of biochar and PGPM narrow down the microbial community and helps in specific microbiota in the rhizospheric soil and plant roots (Zhou et al., 2024). These conditions favor beneficial microbes like Bacillus spp., Pseudomonas spp., Streptomyces spp., Trichoderma spp., Serendipita spp. etc., while limiting the load of soil-borne microbes like Fusarium, Rhizoctonia, Macrophomina, Ralstonia, etc (Kumar et al., 2024). Their increased population has a much larger antagonistic effect, providing defense to plants against soil-borne pathogens. The antagonistic effects include competition, parasitism and antibiosis. The biochar, along with PGPB or beneficial fungi, produces lytic enzymes, siderophores and other secondary metabolites that suppress the growth and production of soil-borne pathogens (Hossain et al., 2025). Biochar combined with Bacillus spp. also favors the housing of parasitic and predatory protists like Cercomonas and Paracercomonas, which inhibit the growth of soil-borne pathogens (Yan et al., 2024). Biochar alters the physico-chemical properties of the soil rhizosphere, which houses the soil microorganisms, by increasing the porosity, aggregate stability and hydrophobicity in the soil rhizosphere. Moreover, the number of secondary plant roots and root hairs is also increased due to all this, which leads to more intake of water and nutrients from the soil, making the plant more robust and healthier. The biochar and microbes activate the resistance genes, which further stimulate the secondary metabolites, inducing resistance in plants (Kumari et al., 2024). Biochar does not necessarily cause direct toxicity to the pathogens, but it re-engineers the system by shifting the soil-root-microbe-plant system toward microbial diversity, nutrient enrichment and plant defense activation (Asif et al., 2023). Therefore, application of biochar-microbes provides new avenues for sustainable plant protection.

Table 6. Biochar-microbial combinations mitigating soil-borne pathogens to improve crop yield.

5 Challenges in field applications and long-term stability

Biochar and microbial inoculants have great promise to improve soil health and crop yield, but their successful application from controlled experiments to field-scale agricultural systems is a big issue. Most research has been conducted in greenhouse or laboratory conditions, where temperature, moisture, nutrient availability and microbial competition are carefully controlled. In contrast, the field environment is highly dynamic and varied, leading to large geographical and temporal variability of biochar effectiveness and microbial establishment. This is the reason that favorable results under controlled conditions are not always consistently duplicated under practical agricultural situations. A critical difficulty is the persistence of introduced microbial inoculants following field treatment. Beneficial microorganisms often have to compete with resident microbial communities for resources, ecological niches and root colonization sites (Scholten, 2025). Other environmental challenges like drought, flooding, salinity and temperature variations may also further limit microbial survival and metabolism. Therefore, the initial benefits of inoculation are generally lost over time, reducing the long-term effectiveness of microbial compositions. Another problem is the durability of microbial consortia, because interactions between consortium members can be affected by environmental circumstances and hence modify their functional performance in the rhizosphere. The long-term usefulness of biochar is also influenced by the aging processes in soil following application. Freshly formed biochar provides homes and reactive surfaces for microbial colonization, but its physicochemical qualities alter progressively through oxidation, weathering and interactions with soil organic matter and mineral particles. Such changes can influence surface functional groups, nutrient retention ability and adsorption properties and thereby affect microbial community assembly and nutrient cycling activities. Thus, biochar can have different ecological functions throughout time and long-term monitoring is necessary to understand the sustained effects of biochar on soil ecosystems. Another major problem is the complexity of interactions between biochar, microbes and soil. Biochar-induced changes in soil pH, moisture retention, aeration and nutrient availability can alter microbial community structure and activity, but these reactions are frequently highly site-specific. The variable outcomes among research are further attributed to the differences in feedstock source, pyrolysis settings, soil type and meteorological factors. Therefore, elucidating mechanistic links between biochar physicochemical qualities, microbial ecology and nutrient transformation pathways and plant physiological responses is still an important research focus. Field-scale application requires standardized application procedures and climate-specific optimization strategies. The ideal biochar type, application rate and microbial formulation may change substantially among agricultural systems and environmental conditions. Thus, long-term multi-location field trials incorporating agronomic, microbiological and ecological evaluations can be used to assess durable, resilient and economically feasible biochar-microbial technology. Such issues are critical to establishing reproducible and scalable approaches to improve soil health, increase nutrient-use efficiency and support climate-resilient agricultural production systems.

6 Conclusion and perspective

Although much progress has been made in understanding the benefits of biochar and microbial inoculants for sustainable agriculture, there are still some fundamental knowledge gaps in understanding the mechanisms driving their interactions in soil-plant systems. Future research must move beyond single agronomic result evaluations to the development of mechanistic frameworks that integrate biochar physicochemical properties, microbial community dynamics, nutrient cycling processes and plant physiological responses under a variety of environmental conditions. Such an approach would provide a systems-level knowledge of how changes in soil structure, pH, porosity, surface functional groups and nutrient retention induced by biochar affect microbial assembly, functional gene expression and plant performance. The application of multi-omics technologies, such as metagenomics, metatranscriptomics, metaproteomics and metabolomics, gives great opportunity to reveal the complex interactions between biochar, microbes and plants. Use of these methodologies in combination with network analysis and ecological modeling may identify essential microbial taxa, metabolic pathways and functional features that underpin nutrient transformation, stress reduction, carbon sequestration and disease suppression. This information is critical for the logical design of next-generation microbial inoculants and biochar-based delivery systems. Future research should also focus on biochar engineering methodologies to design its physicochemical qualities for specific agricultural purposes. Alterations in feedstock choice, pyrolysis parameters, surface functionalization and nano-biochar synthesis might improve nutrient retention, pollutant immobilization, microbial colonization and rhizosphere function. Similarly, the design of synthetic microbial consortia should evolve from the use of single-strain inoculants to the assembly of functionally complementary communities that can execute multiple ecosystem services by biological nitrogen fixation, phosphorus solubilization, phytohormone production, pathogen suppression and stress tolerance. Such research would validate over the long-term biochar-microbial technologies in different soil types, cropping systems, and climates. Most evidence available today is from short-term greenhouse or lab studies, which limit our understanding of stability, resilience and economic viability under real agricultural conditions. Strategies must be specific to climate variation in terms of temperature, precipitation, soil properties and environmental stresses on biochar and microbial performance. Sustainable soil management in the future will be the integration of biochar engineering, microbial ecology, multi-omics technologies and precision agriculture.

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Footnotes

Edited by: Prabir K. Kolay, Southern Illinois University Carbondale, United States

Reviewed by: Ugo De Corato, Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), Italy

Haider Sultan, Jianghan University, China