Black shank disease in tobacco, caused by Phytophthora nicotianae , can lead to yield losses of 30%–50% upon outbreak. Recently, biochar derived from agricultural waste has shown significant potential in controlling soil-borne diseases, though its mechanisms remain unclear. Over a 3-year observation period, we found that the incidence of black shank was significantly lower in plots amended with biochar compared with normal cultivation plots. To investigate the underlying mechanisms, we studied both the direct and indirect effects of biochar on black shank. Direct antifungal assays indicated that biochar reduced the total number of sporangia by 53.91%. Further pot experiments revealed a 62.34% reduction in the P. nicotianae population in the soil following biochar application. Additionally, biochar application led to notable changes in soil physicochemical properties and microbial community composition. Microbial species analysis showed that biochar promoted the aggregation of beneficial microbes such as Sphingomonas , Flavisolibacter , and Mucoromycota . Functional predictions using the PICRUSt 2 software revealed that biochar enhances bacterial functions related to antimicrobial substance synthesis (Tetracycline biosynthesis), detoxification metabolism (D-arginine and D-ornithine metabolism, arginine and proline metabolism), and lipid and fatty acid metabolism (Lipopolysaccharide biosynthesis, fatty acid biosynthesis), while fungal functions showed no significant changes. This suggests that rhizosphere bacteria play a more prominent role in the suppression of black shank by biochar, a finding supported by partial least squares path modeling analysis. Therefore, we hypothesize that biochar not only directly inhibits P. nicotianae growth but also regulates the composition of the rhizosphere microbial community, inducing the production of antimicrobial substances by rhizosphere bacteria, effectively preventing P. nicotianae invasion. IMPORTANCE: Black shank, a global soil-borne fungal disease in tobacco, currently lacks effective control methods. Notably, biochar derived from agricultural waste has shown significant potential in controlling soil-borne diseases. Over a 3-year observation period, we found that plots amended with biochar had a significantly lower incidence of black shank compared with normal cultivation plots. However, the mechanisms of disease suppression remained unclear. Through in vitro antifungal assays and pot experiments, we discovered that tobacco-derived biochar can directly inhibit the growth of the pathogen. Additionally, biochar regulates the composition of the rhizosphere microbial community, inducing rhizosphere bacteria to produce antimicrobial substances, effectively preventing pathogen invasion. This discovery reveals both the direct and indirect mechanisms by which biochar suppresses black shank in tobacco. It provides a scientific basis for developing green control technologies for black shank and offers theoretical support for the application of biochar in managing soil-borne diseases in tobacco cultivation areas.

Introduction: Phenolic acids are believed to play a significant role in tobacco continuous cropping obstacles, but the strength and potential mechanisms of different phenolic acids remain unclear.Methods: This study evaluated the allelopathic effects of six phenolic acids that exhibited cumulative effects in our previous research. Different concentrations of phenolic acids with the strongest allelopathic effects were added to potting soil to explore their impacts on tobacco growth and physiological characteristics, as well as on soil chemical properties and microbial community structure. Results: The results showed that coumaric acid exhibited the strongest direct allelopathic effect. Exogenous coumaric acid significantly reduced soil pH and shifted the soil microbial community from bacteria-dominated to fungi-dominated. Simultaneously, the abundance of bacteria related to nutrient utilization (e.g., Flavisolibacter, Methylobacterium) and fungi related to disease resistance (e.g., Fusicolla, Clonostachys) gradually decreased, along with a reduction in soil catalase, urease, invertase, and acid phosphatase activities. Leaf MDA levels increased continuously with higher concentrations of coumaric acid, while the root resistance hormone (jasmonic acid and the jasmonate-isoleucine complex) levels show the opposite trend.Discussion: Coumaric acid may inhibit tobacco growth by influencing the physiological processes in tobacco plants directly and the broader soil microecological balance indirectly. This study provides theoretical guidance for precise mitigation of continuous cropping obstacles in future tobacco cultivation.

Nicotine, a potential environmental pollutant that has raised increasing concerns, accumulates to significant levels in soils under long-term tobacco monoculture, posing substantial risks to both local ecosystems and human health. Addressing this challenge, the screening and utilization of nicotine-degrading bacteria have emerged as a central remediation strategy. In this study, we isolated nicotine-degrading bacteria from tobacco-cultivated soils and subsequently immobilized them onto biochar to optimize degradation efficiency. A systematic investigation was conducted to examine the synergistic effects and underlying degradation mechanisms of the biochar-bacteria complex. Notably, we successfully isolated Paenarthrobacter ureafaciens N21 (N21), a bacterial strain capable of degrading nicotine through the pyridine pathway. When immobilized on biochar (BN21), the composite maintained robust degradation capabilities in both culture media and soil environments. Compared with free N21, BN21 demonstrated a 1.4 times enhancement in nicotine degradation efficiency and significantly improved colonization capacity by the degrading bacteria (P < 0.0001). Stability assessment tests further confirmed BN21's consistent degradation performance under diverse environmental conditions. Integrated microbiomic and metabolomic analyses revealed that BN21 induced significant alterations in soil microbial community structure and metabolic profiles, while enhancing the soil's resistance to repeated nicotine disturbances. Importantly, BN21 facilitated synergistic interactions between nicotine-degrading bacteria and indigenous microorganisms, collectively mediating nicotine decomposition through coordinated pyridine and pyrrolidine pathways. The novel discovery of bacteria-loaded biochar synergistically enhancing nicotine removal highlights the potential of biochar-microbe composites for targeted pollutant elimination. This approach shows promising prospects for future applications in ecological remediation of various organic contaminants, providing innovative perspectives for developing microbiome-based green remediation strategies.

Introduction: Applying biochar (BC) to reduce toxic substance accumulation in soil, either through direct adsorption or modulation of the microbial community, has received considerable attention. However, a knowledge gap exists regarding how BC regulates microbial community structure and functions to mitigate toxic substance accumulation.Methods: We previously identified p-coumaric acid (p-CA) as a representative autotoxin in tobacco rhizosphere soil. On this basis, this study simulated a soil environment with p-CA accumulation to investigate the impacts of BC on p-CA, soil physicochemical properties, and microbial community structure and function.Results: The results showed that p-CA could be directly adsorbed onto BC, which followed the pseudo-second-order kinetic model (R² = 0.996). A pot experiment revealed that BC significantly reduced soil p-CA, altered soil microbial composition, and enhanced bacterial community diversity. A weighted correlation network analysis showed a close association between taxon 1 in the microbial network and p-CA, suggesting a pivotal role for this taxon in reducing p-CA, with Devosia and Nocardioides identified as potential key contributors to this process. The prediction of possible keystone taxa functions showed that BC increased the relative abundances of aromatic compound degraders. Mantel tests indicated that soil organic matter exerted the greatest influence on keystone taxa functions and hub genera.Discussion: These findings suggest that BC may either directly chemisorb p-CA or indirectly facilitate p-CA degradation by regulating the functioning of keystone taxa. The results of this study provide a novel perspective for further investigation of the mechanisms through which BC reduces the accumulation of toxic substances in soil.

This study conducts an integrated analysis of the impacts of tobacco cultivation on farmers in Yunnan Province using machine learning and econometric methods, drawing on detailed micro-level survey data collected from 253 households. Our findings highlight the significant role of tobacco income within household income structures, demonstrating its competitiveness compared to other crops. Through interpretable machine learning techniques and advanced econometric methods, the analysis reveals that expanding tobacco cultivation is associated with improvements in certain indicators of farmers’ quality of life, although the benefits vary with the scale of production. Additionally, the promotion of agricultural diversification by the Tobacco Bureau has shown positive effects, despite challenges such as localized disadvantages, such as poor soil quality, limited access to irrigation, and remoteness from markets. The results emphasize the need for optimizing cropping structures by adjusting crop combinations, planting schedules, and resource allocation to improve yield and sustainability and improving management practices to maximize the benefits of tobacco cultivation while supporting sustainable agricultural development.

Stacking, a pivotal step in the preparation of composted organic manures, plays a crucial role in organic matter decomposition, nutrient availability, and soil microbial diversity, with effects dependent on the stacking duration. However, the mechanisms through which organic manures with different stacking times influence crop growth and development via alterations in the soil environment remain poorly understood. This study employed a pot experiment with tobacco plants, applying conventional fertilizers alongside organic cottonseed meal manures subjected to various stacking times (0, 10, 20, and 30 days). The primary aim was to examine the impact of cottonseed meal organic manures on the microbial community structure, function, and chemical properties of tobacco-growing soil, as well as to assess dry matter accumulation in tobacco plants. Results revealed that, compared to conventional fertilizers alone, the addition of cottonseed meal organic manures significantly enhanced soil organic matter content, with the 20d-stacked manure showing the highest increase (68.94%). Additionally, the composition of the soil microbial community was modified, which has increased the relative abundance of carbon and nitrogen metabolic functions. Dry matter accumulation in tobacco plants increased by 13.66%, 25.83%, 31.65%, and 9.69% across the different stacking times. In conclusion, composted organic manures regulate the soil–microbe system, promoting tobacco growth by enhancing the microbial structure of rhizosphere soil and improving nutrient availability. Cottonseed meal organic manures subjected to 20d of composting exhibited the most comprehensive benefits. The enrichment of beneficial microbes like Chryseobacterium and Humicola (potential antagonists of soil pathogens) might contribute to the observed enhancement in soil organic matter and available nutrients. This improvement in soil quality led to a balanced nutrient environment, ultimately promoting dry matter accumulation in tobacco plants. These findings offer robust theoretical support for the application of composted organic manures. IMPORTANCE: This study is important because it elucidates the crucial mechanisms by which composted organic manures, specifically through the regulation of the soil–microbe system, promote crop growth. It provides key evidence that the stacking duration is a critical factor, identifying a 20-day (d) composting period for cottonseed meal manure as optimal for delivering comprehensive benefits: (i) Enhanced soil health: significantly increasing soil organic matter and improving nutrient availability. (ii) Improved microbial community: shifting the soil microbial structure to favor beneficial bacteria and suppress pathogens, thereby enhancing metabolic functions related to carbon and nitrogen cycling. (iii) Direct crop promotion: leading to a substantial increase in dry matter accumulation in tobacco plants