A new strategy for evaluating the improvement effectiveness of degraded soil based on the synergy and diversity of microbial ecological function

•Nitraria sibirica growth are improved under the organic fertilizer and AMF amendment.•Combination of organic fertilizer and AMF improves the phytoremediation of sandy soil.•Combination of organic fertilizer and AMF alters microbial community of sandy soil.•Network analysis clarify microbial interactions and ecology functional roles.•Synergy and diversity of microbial ecological function is used to assess soil quality. Sandy soil, as an important transition phase to desertification, has been an important environmental issue of global concern. This study explored the combined effects of organic fertilizer amendment and arbuscular mycorrhizal fungus (AMF)-assisted phytoremediation on sandy soil improvement and revealed the mechanism of soil improvement from the perspective of microbial interactions. Furthermore, soil quality and soil improvement effectiveness were evaluated from the perspective of microbial ecological function. A greenhouse pot experiment with four treatments, including control (CK), single AMF-assisted amendment (RI), single organic fertilizer amendment (OF) and combined amendment (OF + RI) was set up. The results showed that the biomass and nutrient element contents of Nitraria sibirica, soil enzyme activities, soil organic carbon and soil water-stable macroaggregates (>0.25 mm) were highest in the OF + RI treatment. Using Illumina high-throughput sequencing, we found that the combined amendment had a significant impact on soil microbial diversity, community composition and ecological function. Chloroflexi, Basidiomycota, Blastocladiomycota and Sordariomycetes were significantly dominant microorganisms in the OF + RI treatment. Network analysis revealed significantly positive or negative linear relationships between bacteria/fungal groups and soil nutrient elements. In conclusion, the synergy and diversity of microbial ecology function can be used as a key indicator to assess the improvement effectiveness of various soil. Under the combined effects of reasonable nutrient supplementation and effective cooperation of the microbial community, the physicochemical amendment and microbe-assisted phytoremediation will more positively drive sandy soil improvement. This study proposes new insights for effectively evaluating the soil improvement effectiveness and improving sandy soil or managing desertification.