Soil microorganisms are important components of soil ecosystems, and their diversity plays an important role in maintaining their functional stability. Organic fertilizer is an important measure for improving soil fertility in agronomic practice. The effects of organic fertilizer on soil microbial diversity and community structure are different with different degrees of maturation. In this study, uncomposted organic fertilizer (R), high-temperature organic fertilizer (H), cooling organic fertilizer (C), and decomposed organic fertilizer (D) were applied, and the 16S rRNA gene sequences of bacteria in soil were analyzed via high-throughput sequencing technology to understand the effects of organic fertilizer with different degrees of maturation on bacterial diversity and community structure in saline soil. Compared with no fertilization, the uncomposted organic fertilizer, high-temperature organic fertilizer, and decomposed organic fertilizer treatments significantly reduced soil bacterial diversity: the decomposed organic fertilizer treatment significantly reduced soil bacterial richness, the cooling organic fertilizer treatment had no significant effect on soil bacterial diversity and bacterial richness, Proteobacteria representing soil nutrients significantly increased under the cooling organic fertilizer treatment, and the relative abundance of Firmicutes significantly decreased. These four organic fertilizers, with different degrees of maturation, significantly increased the beneficial bacterium Bacillus and nitrile-based degrading bacteria but also significantly increased the potential pathogenicity of the soil, and there was no significant difference between the four treatments. In addition, during a cooling period, the organic fertilizer treatment helped to increase the population of oxidative-stress-tolerant bacteria. The application of organic fertilizer during a cooling period to saline–alkali soil is more helpful in improving its nutrient levels.

Streptomyces alfalfa strain 11F has inhibitory effects on many phytopathogenic fungi and improves the establishment and biomass yield of switchgrass. However, the antagonistic effects of strain 11F on Fusarium wilt of watermelon and its secondary metabolites that contribute to its biocontrol activity are poorly understood. We evaluated the antagonistic and growth-promoting effects of strain 11F and conducted a transcriptome analysis to identify the metabolites contributing to antifungal activity. Strain 11F had marked inhibitory effects on six fungal pathogens. The incidence of Fusarium wilt of watermelon seedlings was decreased by 46.02%, while watermelon seedling growth was promoted, as indicated by plant height (8.7%), fresh weight (23.1%), and dry weight (60.0%). Clean RNA-sequencing data were annotated with 7553 functional genes. The 2582 differentially expressed genes (DEGs) detected in the Control vs. Case 2 comparison were divided into 42 subcategories of the biological process, cellular component, and molecular function Gene Ontology categories. Seven hundred and forty functional genes (55.47% of the DEGs) were assigned to Kyoto Encyclopedia of Genes and Genomes metabolic pathways, reflecting the complexity of the strain 11F metabolic regulatory system. The expression level of the gene phzF, which encodes an enzyme essential for phenazine-1-carboxylic acid (PCA) synthesis, was downregulated 3.7-fold between the 24 h and 48 h fermentation time points, suggesting that strain 11F can produce phenazine compounds. A phenazine compound from 11F was isolated and identified as phenazine-1-carboxamide (PCN), which contributed to the antagonistic activity against Fusarium oxysporum f. sp. niveum. PCA was speculated to be the synthetic precursor of PCN. The downregulation in phzF expression might be associated with the decrease in PCA accumulation and the increase in PCN synthesis in strain 11F from 24 to 48 h. Streptomyces alfalfae 11F protects watermelon seedlings from Fusarium wilt of watermelon and promotes seedling growth. The transcriptome analysis of strain 11F provides insights into the synthesis of PCN, which has antifungal activity against F. oxysporum f. sp. niveum of watermelon.

Biochar, a soil amendment with diverse regulatory functions, has been widely applied to enhance soil conditions. However, its underlying mechanism for alleviating continuous cropping obstacles, from the perspective of rhizosphere microbe-metabolite-plant coupling, remains to be further elucidated. Using cucumber ( Cucumis sativus L.) as the model crop, this study explored the rhizosphere-mediated effects of biochar application under continuous cropping conditions via the analytical methods of metagenomics and metabolomics. Six biochar application rates (0, 5, 10, 20, 30, and 40 t ha ^- ¹) were tested. All biochar treatments significantly improved cucumber yield by 20%-50%, with the C30 and C40 treatments producing the most pronounced yield enhancement. C10, C20, C30 and C40 treatments had a positive effect on cucumber quality, soil physicochemical properties and enzymatic activities. Vitamin C and soluble protein peaked in C20, whereas some sugar indicators decreased across all biochar treatments. Urease activity was significantly elevated under C20, C30, and C40 treatments. Notably, the C40 treatment led to marked increases in total nitrogen, available phosphorus, and sucrase activity. Biochar amendments also enriched key bacterial phyla involved in carbon and nitrogen cycling, including Actinobacteria, Bacteroidetes, Chloroflexi, and Bacillota. Medium to high application rates (C20, C30, C40) upregulated various secondary metabolic pathways associated with biotic stress resistance, including the biosynthesis pathways of phenylpropanoids, various alkaloids, and the metabolic pathway of phenylalanine. High biochar application rate (C40) characterized lipid metabolism as the core responsive pathway and significantly downregulated galactose metabolism. This study reveals that biochar application represents a promising strategy to mitigate continuous cropping obstacles of cucumber by enhancing nutrient cycling, enzyme activities, soil metabolite composition, and the rhizosphere microbial community in facility systems of the cold and arid northern regions of China.

[This corrects the article DOI: 10.3389/fpls.2026.1726191.].