Continuous Cropping Stress on Ophiopogon japonicus and Alleviation by Maize Intercropping: Rhizosphere Microecological Mechanisms

Long-term continuous cropping of Ophiopogon japonicus leads to continuous cropping problems, and this practice threatens the long-term viability of O. japonicus production. Currently, the intrinsic relationship between the deterioration of soil physicochemical properties and the disruption of the rhizosphere microbial community caused by continuous cropping of O. japonicus remains unclear. This study aims to elucidate the mechanisms underlying continuous cropping problems in O. japonicus from multiple perspectives, including rhizosphere microecology and soil enzyme activity. This study was conducted in Luxi Town, Santai County, Mianyang City, Sichuan Province, China. Rhizosphere soils of O. japonicus were collected from fields with different continuous cropping years (1, 2, and 3 years) and from a maize–O. japonicus intercropping system. A split-plot design was adopted, with continuous cropping year as the main-plot factor and planting pattern (monocropping and intercropping) as the subplot factor. The experiment compared the differences in metagenomic sequencing, standard soil physicochemical analysis, soil enzyme activity, yield and key components of O. japonicus. The results indicate that long-term continuous cropping leads to soil nutrient imbalance, a significant decline in soil enzyme activity, and reduced O. japonicus yield and quality. The duration of continuous cropping had a highly significant effect on yield (F = 23.611, p < 0.001), while the cropping pattern had a significant effect on yield (F = 15.154, p = 0.003); the interaction between the two was not significant (F = 1.815, p = 0.213). Compared with monoculture, the O. japonicus yields in the intercropping treatments increased by 18.15%, 16.02%, and 13.52%, respectively. Continuous cropping caused a decline in rhizosphere microbial diversity and a restructuring of the microbial community, with a significant decrease in the relative abundance of beneficial bacterial phyla (Actinomycetota, Nitrososphaerota) and an enrichment of potentially pathogenic bacterial genera (such as Fusarium). The regulatory effects of maize intercropping on the microbial community exhibit distinct lag and time-dependent characteristics. In summary, it is the synergistic interaction of multiple factors that acts as a key driver in the formation of continuous cropping stress in O. japonicus, and the second year of continuous cropping is the critical regulatory juncture. This study offers a theoretical basis for alleviating continuous cropping stress via maize intercropping strategies, and in doing so supports the sustainable development of the O. japonicus cultivation industry as well as the improvement and maintenance of the soil ecological environment.