Effects of intercropping on rhizosphere microbial community structure and nutrient limitation in proso millet/mung bean intercropping system

Abstract

Soil microbes are important for nutrient cycling and ecosystem functions in diverse farmland systems. Intercropping systems alter the soil microbial community structure and boost metabolic function via biological interactions between species. However, the responses of microbial communities to nutrient limitation under intercropping conditions remain unclear. In this study, intercropping of proso millet and mung bean was used to investigate the microbial community structures and metabolic characteristics of both species rhizospheres. The relationship between microbial communities and nutrient limitation was analyzed using high-throughput sequencing. Compared with single cropping, the potential nitrogen (N) limitation of rhizosphere soil microorganisms of both species was more intense in intercropping. Linear regression analysis of soil nutrients, microbes, and threshold elemental ratios directly supported this finding. The soil microbial community diversity and composition were significantly affected by intercropping. Redundancy analysis revealed that total carbon:total nitrogen (TC:TN) and β–1,4–glucosidase: (β–1,4–N–acetylglucosaminidase + leucine aminopeptidase) (BG: (NAG + LAP)) ratios were key factors influencing bacterial and fungal community structure. Intercropping altered the topological network properties of soil microbial communities; the ecological connectivity of bacterial taxa was tighter than that of fungi. As dominant microbial communities, the increased relative abundance of Proteobacteria in intercropped mung bean and decreased relative abundance of Ascomycota in intercropped proso millet was conducive to regulating microbial metabolic limitations. Our results highlighted the close relationship between microbial communities and nutrient limitation, improving our understanding of the degree of plant–soil interactions from the perspective of microbial metabolism in proso millet/mung bean intercropping system.