Bulk soil microbial reservoir or plant recruitment dominates rhizosphere microbial community assembly: Evidence from the rare, endangered Lauraceae species Cinmaomum migao

Abstract

The rhizosphere microbial community is important for plant growth and health; however, it remains controversial whether this community assembles through rhizosphere recruitment or the stochastic dispersal of the bulk soil microbial reservoir. We observed the dynamic spatiotemporal changes in the Cinmaomum migao microbial community in the rhizosphere and bulk soil, a rare and endangered species endemic to China, through continuous sampling for 2 years. Soil nutrients, pH, and enzymes were tested to examine the dominant factors underlying rhizosphere microbiome assembly. The rhizosphere microbiome is a subset of the bulk soil microbiome. The Simpson diversity index (−0.02%, −0.01%) and Shannon diversity index (−4.3%, −4.5%) were lower in the rhizosphere than in the bulk soil. The rhizosphere microbial network had 1073 nodes and 2899 edges in the first year and 1012 nodes and 2730 edges in the second year. In contrast, the bulk soil microbial network had 1088 nodes and 3717 edges in the first year and 1133 nodes and 3715 edges in the second year. Therefore, their community compositions are very similar in terms of higher taxonomy (e.g., phylum), but significantly different in terms of lower taxonomy (e.g., genus). However, functional composition is significantly different between rhizosphere and bulk soil microbiomes; the rhizosphere community is closely associated with the nitrogen and carbon cycles, whereas bulk soil microbiome is highly diverse and its functioning varies with its location. Our study revealed that plant roots play an important recruitment role when they encounter different bulk soil microbial reservoirs. However, they may form bulk soil microbial reservoir with similar functions through chance selection and not assembly taxonomic level.