Effects of arbuscular mycorrhizal fungi on the improvement and restoration of degraded landscape soil in the ionized rare earth mining area of the southern region of Jiangxi in subtropical China

The disordered mining of ion-type rare soil has caused significant ecological and environmental problems. Arbuscular mycorrhizal fungi (AMF) can promote soil quality, providing new ideas about the ecological restoration of degraded soil. In this study, the degraded ion-type rare earth tailing soils in Xinfeng County, southern Jiangxi Province, was used as a research object. The soil was subjected to different restoration methods (biochar + fly ash + surface vegetation planting) for 2 yr. A total of six treatments were set up in this experiment, and the phospholipid fatty acid method was used to determine the microbial community structure and biomass of the rhizosphere soil of navel oranges [Citrus sinensis (L.) Osbeck] treated with different amounts of biochar (0, 1, and 5%) plus surface mulching (Trifolium repens L.) or soil without plants. Additionally, a pot experiment was conducted to study the effects of single and double inoculation of AMF (Septoglomus viscosum and Claroideoglomus claroideum) on plant growth and soil improvement under various P levels (0 and 50 mg kg–1) in ion-type rare soil. The results showed that the microbial biomass (fungi, Gram-positive bacteria, Gram-negative bacteria, actinomycetes, AMF, and protozoa) when T. repens was present was noticeably higher than that when T. repens was not present. In particular, the biomass of the AMF under the T. repens treatment with 5% biochar (1.28 nmol g–1) was 34.38% higher than that under the 5% biochar treatment without plants (p < .05). Furthermore, the pot experiments showed that AMF inoculation significantly increased the plant biomass, single AMF inoculation significantly increased soil P in the absence of basal P, and double inoculation significantly increased the glomalin (a component of soil organic matter) content. Our findings indicated that the soil microbial biomass was greatly affected by planting T. repens and adding biological modifiers. These composite remediation methods could provide an increasing number of C sources for the soil microbial community and could effectively improve soil quality and plant growth.