Molecular Soil Biology 2026, Vol.17, No.1, 38-50 http://bioscipublisher.com/index.php/msb 40 continuous cropping but also noted decreases in enzyme activities related to nutrient mineralization such as phosphatase and urease, which are critical for converting nutrients into plant-available forms (Zhao et al., 2017; Huang et al., 2025). This decoupling between nutrient presence and availability can impair efficient nutrient uptake by cucumbers. Microbial communities play a central role in mediating nutrient cycling under continuous cropping conditions. Changes in microbial diversity and function influence key processes such as nitrogen fixation, phosphorus solubilization, and organic matter decomposition. Research indicates that beneficial microbial taxa involved in nitrogen and phosphorus cycling decline with prolonged monocropping while potentially pathogenic microbes increase. For instance, rotation systems that enrich microbiota antagonistic to pathogens also enhance functional genes associated with nitrogen and phosphorus cycling compared to continuous cucumber monoculture (Zhang et al., 2023; Xu et al., 2025). These microbial shifts directly affect nutrient transformations and availability, underscoring the need for management strategies that support healthy microbial-mediated nutrient cycling. 2.3 Changes in the stability of soil micro-ecosystems The stability of soil micro-ecosystems is compromised under continuous cucumber cropping due to altered microbial community composition, reduced diversity, and disrupted interactions among microorganisms. Continuous monoculture tends to decrease fungal diversity while increasing certain bacterial groups linked with stress or disease conditions. For example, long-term mono-cropping has been shown to reduce beneficial bacterial phyla such as Actinobacteria while increasing Acidobacteria and Firmicutes; similarly, fungal communities shift toward dominance by Ascomycota species often associated with pathogenicity (Zhao et al., 2020). These changes weaken the resilience of the soil microbiome against environmental stresses and pathogen invasion. Network analyses reveal that continuous cropping leads to more complex but less cohesive microbial interaction networks characterized by higher connectivity but reduced clustering among fungi, indicating destabilization of micro-ecosystem structure over time (Huang et al., 2025). Moreover, reductions in key enzyme activities further impair ecosystem functions essential for maintaining soil health. Interventions such as biochar amendment combined with intercropping have demonstrated potential for restoring micro-ecosystem stability by improving microbial diversity, reducing salinity stress, enhancing nutrient availability, and promoting beneficial microbial taxa (Shen et al., 2025). Maintaining stable micro-ecosystems is therefore critical for sustaining productive greenhouse cucumber cultivation under intensive continuous cropping regimes. 3 Structure and Function of Soil Microbial Communities 3.1 Composition characteristics of soil bacteria, fungi, and actinomycetes Soil microbial communities under continuous cucumber cropping are characterized by shifts in the relative abundance and diversity of bacteria, fungi, and actinomycetes, which play distinct roles in soil processes. Bacterial communities often dominate in terms of abundance and are highly responsive to changes in soil physicochemical properties caused by monocropping. Key bacterial phyla such as Proteobacteria, Acidobacteria, and Actinobacteria fluctuate with cropping duration, with Actinobacteria often declining under continuous monoculture while Acidobacteria may increase, reflecting altered nutrient availability and soil conditions (Chen et al., 2024). Fungal communities also undergo compositional changes; Ascomycota typically become more dominant in continuous cropping systems, sometimes linked to increased pathogen presence, while beneficial groups like arbuscular mycorrhizal fungi (AMF) may decline without crop rotation or soil amendments (Labouyrie et al., 2023; Wooliver et al., 2025). Actinomycetes, a group of filamentous bacteria important for organic matter decomposition and antibiotic production, tend to decrease in diversity and abundance under long-term monocropping due to soil degradation and reduced organic inputs. This decline can weaken natural disease suppression and nutrient cycling functions. However, management practices such as organic amendments or crop rotations can help restore actinomycete populations by improving soil structure and nutrient status (Chen et al., 2024; Mishra et al., 2025). Overall, continuous cucumber cropping leads to a less balanced microbial community composition with potential increases in pathogenic fungi and decreases in beneficial bacteria and actinomycetes that support soil health.
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