Effects of Altitude and Continuous Cropping on Arbuscular Mycorrhizal Fungi Community in Siraitia grosvenorii Rhizosphere

Siraitia grosvenorii, a medicinal plant with continuous cropping, is cultivated in southern China. Changes in the soil microbial community during continuous cropping can cause soil-borne diseases in S. grosvenorii. This experimental study aimed to determine the differences in the arbuscular mycorrhizal fungi (AMF) community structure and root colonization in the rhizosphere soil of S. grosvenorii with different continuous cropping years and altitudes. We tested three altitude gradients (low, 200-300 m; middle, 500-600 m; and high, 700-800 m) and four continuous cropping years (1, 2, 3, and 5 years). AMF colonization, along with AMF spore density, and the soil physicochemical properties of S. grosvenorii roots at different altitudes and continuous cropping years were determined. Illumina high-throughput sequencing was used to determine the molecular diversity of AMF in the rhizosphere of S. grosvenorii as they exhibited a symbiotic relationship. The AMF species in the rhizosphere soil of S. grosvenorii included 28 species of nine genera, including Glomus, Claroideoglomus, Acaulospora, Paraglomus, Ambispora, and so on. With an increasing altitude, the AMF colonization of S. grosvenorii roots increased significantly (p < 0.01); available phosphorus (AP) content was negatively correlated with AMF colonization (p < 0.01). Glomus and Paraglomus were the common dominant genera in the rhizosphere soil of S. grosvenorii planted for 2-5 years at a low altitude and 1 year at middle and high altitudes. The average relative abundance of Glomus increased with increasing continuous cropping years and altitude in the low-altitude and 1-year S. grosvenorii areas, respectively. Slightly acidic rhizosphere soil contributed to AMF colonization and improved the richness and diversity of the AMF community. Our results showed that altitude, AP, and pH are essential factors for predicting AMF infection and community changes in the S. grosvenorii rhizosphere. Here, Illumina high-throughput sequencing was used to study the species resources and community composition of mycorrhizal fungi in S. grosvenorii in the hilly areas of Guangxi, China. This study provides a theoretical basis for the application and practice of mycorrhizal fungi including the isolation and screening of dominant strains, inoculation of mycorrhizal fungi, and exploration of the effects of mycorrhizal fungi on the growth and active ingredients of medicinal plants.

Automated summary

This experimental study aimed to investigate the effects of changes in the soil microbial community during continuous cropping on S. grosvenorii, a medicinal plant cultivated in southern China. The results showed that an increasing altitude led to a significant increase in the AMF colonization of S. grosvenorii roots, while the available phosphorus content had a negative correlation with AMF colonization. The study also revealed the presence of multiple AMF species in the rhizosphere soil of S. grosvenorii, with their diversity and abundance closely related to soil pH.