Molecular Soil Biology 2026, Vol.17, No.1, 38-50 http://bioscipublisher.com/index.php/msb 42 These changes in assembly dynamics coincide with declines in soil organic matter and enzyme activities critical for nutrient cycling, further impacting microbial diversity and ecosystem function under continuous cucumber cultivation. Figure 2 (A) Comparative analysis of bacterial relative abundances at the phylum level. (B) Comparative analysis of relative fungal abundance at the genus level (Adopted from Chen et al., 2025) 4.2 Dynamic changes of beneficial microorganisms and pathogenic microorganisms Continuous cucumber cropping induces dynamic shifts between beneficial and pathogenic microorganisms in the soil, often resulting in reduced populations of plant-growth-promoting microbes alongside increases in pathogens. Beneficial bacteria such as those involved in nitrogen fixation or organic matter decomposition tend to decline over time due to nutrient depletion and unfavorable soil conditions caused by monocropping (Yang et al., 2025). Similarly, populations of beneficial fungi like arbuscular mycorrhizal fungi decrease, weakening symbiotic relationships that enhance nutrient uptake and disease resistance. Conversely, pathogenic microorganisms including certain fungal genera (e.g., Fusarium, Alternaria) and bacterial pathogens tend to increase with continuous cropping duration, contributing to higher disease incidence and reduced crop yields (Chen et al., 2025). The accumulation of pathogen-associated genes correlates with disease severity in long-term monoculture soils, highlighting the risk posed by unchecked pathogen proliferation (Wang et al., 2025). Management strategies such as microbial fertilizer application or crop rotation have been shown to partially restore beneficial microbes while suppressing pathogens, improving soil health under continuous cropping regimes (Qiu et al., 2025). 4.3 Variation characteristics of the abundance of different microbial groups The abundance of specific microbial groups varies markedly with continuous cucumber cropping duration, reflecting shifts in soil environmental conditions and resource availability. Bacterial phyla such as Proteobacteria often decrease over time while Acidobacteria increase, indicating a shift toward microbes adapted to lower nutrient levels and more acidic soils common under long-term monoculture (Ding et al., 2024; Li et al., 2024). Actinomycetes generally decline with prolonged cropping due to reduced organic matter inputs but can be stimulated by amendments that improve soil quality (Yang et al., 2025). Fungal communities show increased relative abundance of pathogenic taxa like Cladosporium and Alternaria during extended continuous cropping periods, while beneficial fungal groups decline or fluctuate depending on
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