[Potential of Arbuscular Mycorrhizal Fungi, Biochar, and Combined Amendment on Sandy Soil Improvement Driven by Microbial Community].

Sandy soils are considered as a significant transition phase to desertification. The effective recovery of sandy soils is of great significance to mitigate the desertification process. Some studies have shown that arbuscular mycorrhizal (AM) fungi and biochar improved the sandy soil, but there have been very few studies regarding the combined effects of AM fungi and biochar amendments on sandy soil improvement. Additionally, the roles of the bacterial and fungal community during the process of sandy soil improvement remain unclear. A greenhouse pot experiment with four treatments, including a control (CK, no amendment), single AM fungi-assisted amendment (RI), single biochar amendment (BC), and combined amendment (BC_RI, biochar plus AM fungi), was set up. This study investigated the effects of different amendment methods on the Nitrariasi birica mycorrhizal colonization, biomass, nutrient (N, P, K, Ca, and Mg) content, soil organic carbon, soil nutrient (TN, TP, and TK) content, and soil water-stable aggregate composition. High throughput sequencing technology was used to investigate the roles of the bacterial and fungal communities during the process of sandy soil improvement. Combined with multiple analysis methods, the improvement mechanisms of different amendment methods were explored. The aim was to provide basic data and scientific basics for reasonably and effectively improving sandy soils. The results indicated that a significant mycorrhiza colonization was observed in the inoculation (RI and BC_RI) treatments, but there was no substantial difference in the mycorrhiza colonization with the RI and BC_RI. Compared with the CK, the shoot biomass and shoot element (N, K, Ca, and Mg) contents were significantly increased in the RI, and the shoot element (N, P, K, Ca, and Mg) contents were significantly increased in the BC and BC_RI; compared with the RI and BC, the root biomass and the root element (P, K, Ca, and Mg) contents were significantly increased in the BC_RI. Compared with the CK, the soil organic carbon contents were significantly increased in the BC and BC_RI, the soil TN contents were significantly increased by 152.54%, and the soil TP and TK contents were significantly decreased by 12.5% and 18.8%, respectively. The proportion of soil aggregates with particle sizes of 0.25-0.05 mm was the highest in each treatment, and the large particle size (>0.25 mm) soil aggregate was significantly increased in the BC_RI. Compared with the CK, the Sobs and Shannon indices of the bacterial/fungal community were significantly decreased in the RI and BC_RI. There was a difference in the microbial community compositions and abundance in the various treatments. The results of the RDA and network analysis were as follows:the effects of AM fungi, biochar, and combined amendment on the soil environment and microbial community structure were significant; in the different amendment treatments, the relationship of the microbial molecular ecological network was significantly changed, and the composition of the core species varied; compared with the RI, there was a higher network connection degree and a richer core species composition in the BC and BC_RI; moreover, the essential role of Rhizophagus intraradices was weaken and the core roles of the other microorganisms (especially bacterial species) were enhanced under the combined effects of biochar and AM fungi. The SEM results demonstrated that the application of AM fungi and biochar could directly affect the bacteria/fungi community structure, and further affect the plant growth and soil properties. The differences in the microbial community structure (especially the change in the microbial interaction) were the key driving factors that led to the difference in the soil improvement effectiveness. In summary, the effects of the different amendment methods on the improvement effectiveness of sandy soils varied. The microbial community played key roles in the process of sandy soil improvement, and there were potential advantages and applications in accelerating the ecological restoration of sandy soils under the combined AM fungi and biochar amendment.