Molecular Soil Biology 2026, Vol.17, No.1, 38-50 http://bioscipublisher.com/index.php/msb 45 In addition to the temporal gradient of continuous cropping years, the study incorporated high-throughput sequencing techniques targeting bacterial 16S rRNA and fungal 18S rRNA gene fragments to characterize microbial communities comprehensively. This molecular approach provided detailed insights into taxonomic composition and relative abundances of key microbial groups across different cropping durations. The integration of soil chemical analyses with sequencing data enabled identification of potential drivers behind microbial community changes associated with continuous cucumber monoculture (Figure 4) (Liu et al., 2020; Zhao et al., 2020). Figure 4 Location of the study site in a calcareous soil region of northern China and schematic representation of greenhouse cucumber monocropping systems used for soil sampling (Adopted from Liu et al., 2020) 6.2 Sequencing and data analysis results of microbial community structure Sequencing results revealed significant alterations in both bacterial and fungal community structures as continuous cropping years increased. Bacterial diversity showed a decline in dominant phyla such as Actinobacteria, while Acidobacteria and Firmicutes increased significantly after eight or more years of monocropping. For fungi, the relative abundance of Ascomycota increased markedly with longer cultivation periods, indicating a shift toward fungal groups often associated with disease development (Zhao et al., 2020). These compositional changes coincided with decreases in soil pH and fungal diversity but increases in soil organic matter and nutrient concentrations like total nitrogen and available phosphorus. Beta diversity analyses demonstrated that bacterial community composition changed significantly with consecutive cucumber cultivation but alpha diversity remained relatively stable. Notably, some beneficial bacterial genera involved in nitrogen cycling decreased over time, while others related to functional adaptation increased. Co-occurrence network analysis indicated that long-term continuous cropping weakened species interactions within bacterial communities, resulting in less complex networks that may reduce ecosystem stability (Liu et al., 2020; Chen et al., 2022). Overall, these findings highlight that continuous cucumber cropping reshapes microbial communities by favoring certain taxa while suppressing others critical for soil health. 6.3 Relationship between continuous cropping years and soil microbial community changes The duration of continuous cucumber cropping was strongly correlated with shifts in soil microbial communities through its effects on soil environmental factors such as pH, organic matter content, and nutrient availability. Redundancy analysis identified soil organic matter and nitrate nitrogen as key drivers influencing bacterial community variation, whereas pH alongside organic matter significantly affected fungal community structure (Zhao et al., 2020; Huang et al., 2023). As continuous cropping progressed, increasing salinity and acidification contributed to declines in microbial diversity and altered functional potentials.
RkJQdWJsaXNoZXIy MjQ4ODYzNA==