Effects of different crop intercropping on quality and rhizosphere soil microbial community of Erigeron breviscapus
Obstacles for continuous cropping severely restrict the sustainable production of Erigeron breviscapus. To screen suitable intercropping crops and clarify their dual effects on plant growth, medicinal quality, rhizosphere nutrients, soil enzyme activity, and microbial communities, a pot experiment was conducted using 3-year continuously cropped soil, with monoculture as the control (CK) and four intercropping treatments: (A) Brassica juncea L., (B) corn, (C) purple garlic, and (D) broad bean. The results showed distinct crop-specific positive and negative effects of intercropping. On the positive side, intercropping with corn and broad bean significantly increased the total flavonoid content; corn and purple garlic intercropping elevated soil catalase and phosphatase activities, while all four intercropping modes improved soil pH, organic matter, and available nutrients and significantly enriched the richness and diversity of rhizosphere bacterial communities, except in the purple garlic treatment. A correlation analysis indicated that the beneficial phylum Actinobacteriota was positively correlated with soil pH and hydrolase activities, and intercropping effectively reduced the relative abundance of pathogenic Fusarium. However, substantial negative drawbacks were observed across all intercropping systems. All intercropping treatments suppressed aboveground leaf development and root morphological indicators of E. breviscapus, and the scutellarin content was significantly lower than CK at all sampling stages. Intercropping with purple garlic drastically reduced fungal community richness and the number of unique fungal operational taxonomic units, which may weaken soil disease-suppressive capacity. Although corn and broad bean partially alleviated rhizosphere microecological degradation caused by continuous cropping, they simultaneously induced irreversible declines in vegetative growth and key medicinal component accumulation. In conclusion, no fully balanced optimal intercropping combination was identified in this pot experiment; corn and broad bean showed partial potential for soil restoration under controlled pot culture conditions; however, their adverse impacts on medicinal quality and plant growth cannot be ignored. Large-scale field positioning trials are urgently required to verify these pot-derived findings and optimize intercropping configuration, planting density, and cultivation regulation before the coordinated intercropping scheme can be applied to field E. breviscapus production to balance soil health, crop growth, and medicinal efficacy.