Molecular Soil Biology 2026, Vol.17, No.1, 38-50 http://bioscipublisher.com/index.php/msb 41 3.2 Functions of microbial communities in soil ecosystems Microbial communities perform essential functions in soil ecosystems including nutrient cycling, organic matter decomposition, disease suppression, and maintenance of soil structure. Bacteria and fungi mediate carbon and nitrogen transformations through enzymatic activities that regulate mineralization and nutrient availability for plants. For example, bacterial communities strongly influence nitrogen cycling processes such as nitrification and denitrification, while fungal communities contribute significantly to phosphorus solubilization and organic matter breakdown (Zheng et al., 2019; Jiao et al., 2021). These functional roles are critical for sustaining cucumber growth under greenhouse conditions where nutrient demands are high. Continuous cropping can disrupt these functions by altering microbial community composition and reducing functional diversity. Declines in key enzyme activities related to carbon degradation (e.g., β-glucosidase) or nitrogen cycling (e.g., urease) have been observed under monoculture systems, impairing nutrient turnover rates (Zheng et al., 2019). Moreover, shifts toward pathogenic fungal dominance reduce the capacity for natural disease suppression. Conversely, diverse microbial communities with balanced bacterial-fungal interactions enhance multifunctionality by supporting multiple nutrient cycles simultaneously (Jiao et al., 2021). Thus, maintaining functional microbial diversity is vital for ecosystem resilience and productivity in continuous cucumber cropping systems. 3.3 Relationship between microbial diversity and soil health Microbial diversity is positively correlated with overall soil health because diverse communities provide redundancy in ecosystem functions that buffer against environmental stresses and disturbances. High microbial richness supports stable nutrient cycling processes, improves soil structure through aggregate formation, and suppresses pathogens via competitive exclusion or antagonism (Banerjee and Van Der Heijden, 2022; Chen et al., 2024). In greenhouse cucumber systems subjected to continuous cropping, declines in microbial diversity often coincide with reduced soil fertility indicators such as enzyme activities and increased disease incidence. Research shows that soils with greater bacterial and fungal diversity exhibit enhanced multifunctionality including improved carbon sequestration and nitrogen retention compared to less diverse soils (Zheng et al., 2019; Jiao et al., 2021). However, the relationship between diversity and function is complex; community composition often has a stronger influence on specific functions than mere species richness alone (Jiao et al., 2021). Management practices that promote microbial diversity-such as crop rotation or organic amendments-can restore degraded soils by reestablishing beneficial taxa that improve nutrient availability and plant health (Mishra et al., 2025). Therefore, preserving or enhancing microbial diversity is crucial for sustaining long-term soil health under intensive greenhouse cucumber cultivation. 4 Effects of Continuous Cropping of Greenhouse Cucumbers on Soil Microbial Community Structure 4.1 Effects of continuous cropping duration on microbial community diversity The duration of continuous cropping in greenhouse cucumber systems significantly influences soil microbial community diversity, often leading to complex shifts in bacterial and fungal populations. Short-term continuous cropping may initially increase bacterial richness due to nutrient inputs and root exudates stimulating microbial growth, but prolonged monoculture typically results in decreased bacterial diversity and altered community composition as soil nutrients become imbalanced and autotoxic compounds accumulate (Li et al., 2024; Chen et al., 2025). Fungal diversity often shows a contrasting pattern, with some studies reporting increased fungal richness under continuous cropping, potentially due to the proliferation of pathogenic fungi favored by monoculture conditions (Qiu et al., 2025; Zhang et al., 2025). Long-term continuous cropping also affects the balance between deterministic and stochastic processes governing microbial community assembly. Deterministic factors such as soil pH, nutrient availability, and crop root exudates strongly shape microbial communities in early years, but with extended monoculture, stochastic processes gain influence, leading to less predictable community structures (Figure 2) (Chen et al., 2025; Wang et al., 2025).
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