This study investigated the effects of bio-organic fertilizer (BF) containing plant growth-promoting bacterium Bacillus velezensis SS-20 on soil properties, microbial community structure, and C/N cycle functional genes. The results showed that compared with chemical fertilizer (CF) and deactivated bio-organic fertilizer (BFD) treatments, BF significantly improved soil physicochemical properties. Soil pH, organic matter, total nitrogen, total potassium, and total phosphorus content under BF treatment were increased by 14.8%, 56.5%, 48.2%, 38.8%, and 58.4%, respectively, compared to the control; soil urease and sucrase activities increased by 3.5 and 2.4 times those of CF treatment, respectively. Meanwhile, BF increased pakchoi yield by 11.2% (vs. CF). BF treatment enhanced the relative abundance of beneficial bacteria Actinomycetota by 28.4% compared with the BFD treatment and raised that of fungi Ascomycota to 1.9 times that of the control. At the genus level, BF significantly enriched biocontrol-relevant genus Pseudogymnoascus, whose abundance reached three times that of CF treatment, while the abundance of potentially harmful genus Penicillium decreased by 82%. BF also led to a high degree of synergy in carbon and nitrogen cycles. Functional gene analysis indicated that BF down-regulated multiple carbon-degrading genes, increased organic nitrogen metabolism genes by 5.3%, and reduced denitrification genes by 13.3%. Overall, bio-organic fertilizer optimized the soil microenvironment, regulated the microbial community structure, and improved C/N use efficiency and plant growth by introducing functional microorganisms and organic matter.

(1) Background: A vegetable eel co-culture system is an economically efficient way of agricultural cultivation, which can have an impact on the soil microbial environment and play a pivotal role in the soil nutrient cycle, but there is little research on its impact on soil ammonia-oxidizing microorganisms. (2) Methods: NovaSeq platform sequencing was employed to investigate the richness, structure, and diversity of soil ammonia-oxidizing microbial communities, exploring the effects of a vegetable eel co-culture system on soil nitrogen cycling. Four different planting treatments were set up: unfertilized without vegetable eel (CCK), fertilized without vegetable eel (CRT), unfertilized with vegetable eel (ICK), and fertilized with vegetable eel (IRT). (3) Results: A vegetable eel co-culture system significantly increased soil pH and decreased bulk density under fertilization conditions. The soil nitrification potential rate was enhanced by a vegetable eel co-culture system to an average of 26.3%. A vegetable eel co-culture system significantly altered the community structure of all ammonia-oxidizing microorganisms, with a significant increase in the richness and diversity of ammonia-oxidizing bacteria (AOB) and comammox clade-A, while fertilization significantly increased the diversity of all ammonia-oxidizing microbial communities. Structural equation modeling (SEM) analysis showed that the main environmental factors affecting the structure of the ammonia-oxidizing microbial community were nitrate and total nitrogen. The number of amoA genes in AOB and comammox clade-B was significantly positively correlated with the soil potential N nitrification rate (PNR), which played a leading role in the nitrification of alkaline vegetable soil. The network analysis revealed that a vegetable eel co-culture system improved the modularity of AOB and comammox clade-B by 13.14% and 5.66%. (4) Conclusions: This study showed that the vegetable eel co-culture system stimulated the evolution of ammonia-oxidizing microbial communities by changing the physicochemical properties, which in turn promoted the soil nitrification reaction.

Environmentally released carbon nanomaterials can alter polycyclic aromatic hydrocarbon (PAH) attenuation in agricultural soils, yet how their properties influence biodegradation in association with contaminant bioavailability and indigenous microbial responses remains unclear. This study compared nano-biochar (NBC), pristine and hydroxylated multi-walled carbon nanotubes (MWCNTs; 4–6 nm and >50 nm) in phenanthrene-contaminated soil, using raw biochar (RBC) as parent reference material. NBC showed the strongest promotion, reaching 68.17% biodegradation at 60 d and a maximum rate of 3.00 mg/kg/d, compared with 58.31% and 2.00 mg/kg/d in the unamended phenanthrene-spiked control. RBC exerted a weaker positive effect, suggesting biochar nanosizing favored biodegradation, accompanied by moderate bioavailability reduction and stimulation of microbial abundance, enzyme activity and diversity. In contrast, MWCNTs inhibited biodegradation, with reduced β-HPCD-extractable phenanthrene, suppressed polyphenol oxidase activity and more pronounced community shifts, while higher abundance of PAH-degradation gene nidA did not correspond to enhanced biodegradation. Pristine MWCNTs showed the lowest initial β-HPCD-extractable phenanthrene and biodegradation rates, whereas small-diameter MWCNTs most strongly limited final biodegradation extent, consistent with greater surface reactivity and intensified cell-contact stress. Hydroxylated MWCNTs exhibited weaker inhibition than pristine counterparts. These findings highlight the importance of material properties in shaping PAH fate and microbial ecology in agricultural soils.

Soil salinization limits sustainable agriculture. This study used a citric acid–FeSO₄ method to create modified chicken manure biochar (MCMB) as a carrier for the plant growth-promoting Bacillus velezensis SS-20, forming a biochar-based microbial agent (JS). A pot experiment included four treatments: CK (control), SS (SS-20 only), JF (MCMB only), and JS (biochar-based agent). The JS treatment significantly improved pakchoi plant height and aboveground fresh weight by 26.33% and 76.62%, respectively, compared to CK. It also lowered soil pH, electrical conductivity (EC), and salt content, while enhancing soil catalase activity by 8.83%. The ameliorative effects of SS and JF were less pronounced than those of JS. The contribution of biochar and SS-20 to the improvement of the soil quality index suggests additive effects with minimal interaction. Redundancy analysis identified EC and total potassium as the key environmental variables influencing microbial community structure at the phylum and genus levels, respectively. JS influenced the relative abundances of candidate lineages, such as Myxococcota, AG11, and Gemmatirosa, as well as functional genes associated with energy metabolism and cell motility. In summary, JS enhanced soil properties, modulated differentially abundant taxa and their metabolic potential, and consequently facilitated pakchoi production in saline–alkali soil. This study offers practical insights for the ecological management of saline–alkali farmland.