Plant-mediated rhizospheric interactions in intraspecific intercropping alleviate the replanting disease of Radix pseudostellariae

Abstract

Traditional agricultural systems increasingly contribute to food and livelihood security worldwide. Previous studies have demonstrated the positive effects of intercropping on crop productivity due to the reduced impact of disease. However, surprisingly few studies to date have explored the mechanisms underlying the alleviation of agricultural replanting disease by intraspecific intercropping. Here, we performed metabolomic, high-throughput sequencing and quantitative PCR analysis to explore the beneficial effects of intraspecific intercropping on Radix pseudostellariae yields, soil metabolite abundance and microbial communities. Our results showed that intraspecific intercropping alleviated the serious replanting disease of R. pseudostellariae. The intercropping increased fungal and bacterial community diversity, increasing the relative abundances of potentially beneficial taxa (e.g., Nitrosomonadales, Nitrospirales, and Pseudomonadales), and decreasing the relative abundances of pathogenic taxa (e.g., Aspergillus and Talaromyces). Quantitative PCR analysis showed intercropping significantly decreased the populations of pathogenic F. oxysporum, and increased the beneficial Pseudomonas spp. and Burkholderia spp. as compared to monoculture. Our findings also suggested that intraspecific intercropping tightened associations within the soil microbiome and promoted microbial co-occurrence. Specifically, we observed that soils subjected to the consecutive monoculture of two plant varieties contained fewer metabolites, while intercropping increased the abundances of metabolites in the second cropping year. The metabolites most reduced after intercropping were negatively correlated with the beneficial taxa Bacillus, Pseudomonas, Nitrobacter, and Penicillium. Thus, intercropping drove changes in root exudate metabolites, which subsequently shaped the rhizosphere microbiome by increasing microbial diversity. This consequently improved soil nutrients and reduced disease in the consecutive monocultures.