No consistency in the mechanism of assembly and potential effects on the host of various dimensions of Eucommia ulmoides rhizosphere microbiota

Background and Aims: Rhizosphere microbiota is regarded as the second genome of plants and can promote plant growth, development and metabolism. However, little is known about the dominant microbial genera, diversity, and mechanisms of assembly of co-occurrence networks of the plant rhizosphere microbiota and their effects on host secondary metabolites. Methods: Using 33 Eucommia ulmoides rhizosphere soil samples from 11 regions of China, the dominant microbial genera, α-diversity, and co-occurrence networks of the rhizosphere microbiota were determined. Their responses to environmental factors (soil and climatic variables) and effects on the host secondary metabolites (assessed by LC-QTOF MS/MS) were then analyzed. Results: The dominant fungal genus and bacterial genus in the E. ulmoides rhizosphere microbiota were Eremothecium (relative abundance, 50.54%) and Sphingomonas (8.33%), respectively. The dominant microbial genera, α-diversity, and co-occurrence network properties significantly differed by region. The three dimensions of the rhizosphere microbiota (dominant microbial genera, α-diversity, and co-occurrence networks) clearly responded inconsistently to environmental factors, with total and available nitrogen having key effects on dominant microbial genera, total nitrogen and rainfall having key effects on α-diversity, and soil organic matter and temperature having key effects on co-occurrence network properties. There were also inconsistent effects on secondary metabolites, with the co-occurrence network properties being significantly correlated with pinoresinol diglucoside, and dominant bacteria genera ( Bradyrhizobium , Streptomyces , Burkholderia , and Mortierella ) being significantly correlated with aucubin. Conclusion: This study provides a new theoretical basis regarding the mechanisms underlying rhizosphere microbiota assembly, and the microbiota effects on host secondary metabolites.