Excessive nitrogen fertilization in sweet potato cultivation poses significant ecological and economic challenges in China, negatively impacting soil health by altering microbial community diversity, enzyme activities, and increasing the risk of stem nematode damage. In this study, we conducted a field trial in Northeast China, applying 0–72 kg of urea-N per hectare to brown soil under a five-year sweet potato cropping system. The results demonstrated that optimal nitrogen fertilization (64.8 kg ha⁻¹) significantly promoted beneficial microbial populations, enhanced soil urease activity, and reduced the incidence of stem nematode disease while maintaining high sweet potato yields.

Stem nematode (Ditylenchus destructor Thorne) is considered one of the most economically devastating species affecting sweet potato production. Biocontrol offers a sustainable strategy for nematode control. This study conducted a pot experiment to evaluate the biocontrol efficacy of Paecilomyces lilacinus CS-Z and Bacillus pumilus Y-26 against the stem nematode, as well as to examine their influence on the bacterial communities in the sweet potato rhizosphere. The findings indicated that B.pumilus Y-26 and P.lilacinus CS-Z exhibited respective suppression rates of 82.9% and 85.1% against the stem nematode, while also stimulating sweet potato plant growth. Both high-throughput sequencing and Biolog analysis revealed distinct impacts of the treatments on the bacterial communities. At the phylum level, B.pumilus Y-26 enhanced the abundance of Actinobacteria but reduced the abundance of Cyanobacteria, with P.lilacinus CS-Z exhibiting similar effects. Additionally, the treatment with B.pumilus Y-26 resulted in increased abundances of Crossiella, Gaiella, Bacillus, and Streptomyces at the genus level, while the treatment with P.lilacinus CS-Z showed increased abundances of Crossiella and Streptomyces. In contrast, the abundance of Pseudarthrobacter was reduced in the treatment with B.pumilus Y-26. Conversely, the application of the nematicide fosthiazate exhibited minor influence on the bacterial community. The findings indicated that the application of P.lilacinus CS-Z and B.pumilus Y-26 led to an increase in the relative abundances of beneficial microorganisms, including Gaiella, Bacillus, and Streptomyces, in the rhizosphere soil. In conclusion, P.lilacinus CS-Z and B.pumilus Y-26 demonstrated their potential as environmentally friendly biocontrol agents for managing stem nematode disease of sweet potato.

Arbuscular mycorrhizal (AM) fungi establish mutualistic symbioses with plant roots, enhancing plant growth and improving soil fertility through nutrient exchange. Among these, soil nitrogen (N) and phosphorus (P) are critical for symbiosis formation, directly influencing nutrient uptake and translocation within the symbiotic system. This study aimed to examine the regulatory roles of N and P levels on AM fungal development and associated bacterial communities in culture. Sorghum was used as the host plant in pot experiments with two AM fungi, Rhizophagus irregularis and Funneliformis mosseae, under varying N and P concentrations. The analyzed parameters included mycorrhizal colonization, propagule production, plant biomass, nutrient contents (N, P, and K), and bacterial community diversity. N3P1 treatment (150 mg/L N, 30 mg/L P) yielded the highest colonization rate, spore production, and arbuscule abundance in both AM fungal symbionts. At equivalent N and P concentrations, the N, P, and K contents in inoculated plants were significantly higher than those in controls. AM fungal inoculation markedly increased the bacterial diversity in the culture (Shannon index raised by 15.2–28.7%) and enriched beneficial taxa, such as Bradyrhizobium and Pseudomonas. N and P concentrations substantially influenced AM fungal symbiosis, with optimal development observed under N3P1 conditions. By regulating AM symbiotic establishment, N and P levels reshaped microbial community composition, providing theoretical guidance for industrialized AM fungal cultivation and inoculant production.

Aqueous ammonia can release high nitrogen inorganic substances of ammonia and has been used as soil fumigant. However, the information about how fumigation with ammonia affects the soil microbial community is still limited. In this study, a laboratory microcosm experiment was conducted to evaluated the effectiveness of ammonia fumigation in controlling root-knot nematodes (RKNs), its influence on soil microbial diversity, and its impact on nitrous oxide (N ₂ O) emissions. The results indicated that Ammonia treatment increased N ₂ O emissions and decreased the RKNs population by 75.73%. Adding the inhibitors N-(N-butyl) thiophosphoric triamide (NBPT) and Dicyandiamide (DCD) to aqueous ammonia can mitigate N ₂ O emissions. Compared with CK treatment, Soil enzyme activities, including those of urease, nitrate reductase, and nitrite reductase, were enhanced in each treatment. The fungal Sobs index was significantly higher in CK treatment than in the other treatments, whereas bacterial alpha diversity remained unaffected. This study also indicates that soil fumigation with aqueous ammonia has the potential to regulate fungal communities and important key reactions involved in nitrogen cycling.