The phosphoric acid extract of fresh biochar and its compound aqueous solutions promoted tobacco plant growth by regulating nutrient-related microorganisms in rhizosphere soil

Biochar has been widely used in agriculture and has positive effects on soil improvement. To further explore the biochar soil plant interaction mechanisms, rice husk biochar and root-promoting solutions were used to prepare biochar extracts and compound aqueous solutions, to study the effects of biochar acid extract and its compound aqueous solutions on main nutrients content (nitrogen, phosphorus, potassium), microbial abundance and functional diversity in tobacco rhizosphere soil, and their regulation on the growth of flue-cured tobacco (Nicotiana tabacum L.). In this paper, the results showed that, applying biochar acid extract and Its compound aqueous solutions at different concentrations significantly enhanced tobacco plant dry matter accumulation, improved soil pH, increased available nitrogen and organic matter, and reduced potassium and phosphorus availability. Notably, the compound aqueous solutions had a more pronounced effect on soil nutrients compared to biochar acid extract. Regarding the microbial community structure, biochar acid extract and compound aqueous solutions increased the relative abundance of specific bacterial genera, including Sphingomonas and Vicinamibacteraceae, and fungal genera such as Mortierella and Penicillium. biochar acid extract and compound aqueous solutions positively influenced functional groups like chemoheterotrophs, aerobic chemoheterotrophs, and saprotrophs. Sphingomonas contributes to regulating soil pH and decomposing various organic compounds, while Vicinamibacteraceae play a critical role in nitrogen cycling and nutrient availability. The saprotrophic fungus Mortierella can release organic acids to solubilize phosphorus in soils, and Penicillium enhance phosphorus cycling and availability, improving soil nutrient content. Additionally, the application of biochar acid extract and compound aqueous solutions increased the complexity and interconnectivity of the soil microbial network. Notably, the biochar acid extract treatment group showed a stronger positive correlation with soil microbes than the compound aqueous solutions group. In summary, the application of biochar acid extract and its compound aqueous solutions improve soil nutrients by enhancing the structure, diversity, and functional groups of the soil microbial community, thereby promoting tobacco growth.