Effects of arbuscular mycorrhizal fungal inoculation on soil bacterial diversity in the root envelope of licorice

To reveal the effects of arbuscular mycorrhizal (AM) fungi on the bacterial community of plant root enclosures in the field, this study was conducted with Glycyrrhiza uralensis inoculated with Glomus mosseae (Gm) or Glomus intraradices (Gi) and a control without inoculation (CK). High-throughput sequencing was used to analyze the bacterial community diversity, structure, function, and drivers underlying differences among the inoculation treatments. The results showed that inoculation with AM fungi (Gi and Gm) significantly altered the soil nutrient content and significantly increased (P < 0.05) the fast-acting phosphorus content and pH compared with the CK treatment. The dominant bacterial phyla in all three treatments were Proteobacteria (33.17%), Acidobacteria (14.83%), and Actinobacteria (8.73%), and the relative abundance of Acidobacteria and Bacteroidetes in the Gi treatment was significantly lower than that in the Gm and CK treatments (P < 0.05). Functional predictions by PICRUSt2 revealed that the functional bacterial communities of licorice root enclosures under the Gi, Gm, and CK treatments were associated with amino acid metabolism, coenzyme vitamin metabolism, and glycoconjugate metabolism; however, the bacterial communities associated with carbohydrate metabolism, lipid metabolism, and glycan biosynthesis and metabolism were significantly lower in the Gi treatment than the Gm and CK treatments. A redundancy analysis (RDA) revealed that physicochemical properties significantly influenced the distribution of bacterial communities and the available phosphorus (AP) and total phosphorus (TP) were the main drivers underlying the differential distribution of bacterial communities. In summary, the content of soil AP in the root enclosure of licorice inoculated with AM fungi (Gi and Gm) was significantly greater than that in the CK (P < 0.05) and the AP content in the Gi treatment was significantly greater than that in the Gm treatment (P < 0.05); however, the metabolism of sugars and lipids in the Gi treatment was significantly lower than that in the Gm and CK treatments. These findings suggest that Gi may inhibit the metabolism of soil sugars and lipids and that AM fungal inoculation may affect the soil bacterial community by altering P effectiveness in the root enclosure of licorice and thus the distribution of the soil bacterial community.