[Response of Soil Microbial Community Composition to Topography in the Yellow River Source Basin]

The aim of this study was to find out the influence of different topography types on the soil microbial community and its ecological function in the Yellow River source basin unit. An alpine meadow with three types of microtopography （shady slope， sunny slope， and floodplain） was taken as the research object， and the changes of soil microbial community structure， diversity， and molecular ecological network under different microtopography types were explored by combining high-throughput sequencing technology and function prediction. The results showed that： ① There were 1 268 species of bacteria in the three types of microtopography， among which the number of bacteria endemic to the sunny slope habitat was the highest， and the main dominant bacteria at the phylum level were Actinobacteria， Proteobacteria， and Acidobacteriota. There were 316 species of fungi， among which the number of fungi endemic to shady habitats was the highest， accounting for 6.65%. The dominant fungi at the phylum level were Ascomycota， Mortierellomycota， and Basidiomycota. ② The Shannon index， Simpson index， and Pielou index of soil bacteria were significantly different in different landforms， while the Ace index and Chao1 index of soil fungi were significantly different in different landforms， and bacterial community diversity was more responsive to micro-topography than fungi. ③ The topological characteristics of the network showed that the complexity of the network of soil bacteria in the flood plain habitat was high， and the network showed mainly positive correlation， with the largest number of edges （481）. The complexity of the network of soil fungi in the river beach habitat was high， and the network showed mainly positive correlation， with the largest number of edges （393）. ④ The Mantel experiment showed that the bacterial community structure was mainly affected by the changes of plant evenness index， plant aroma index， total nitrogen， and total phosphorus， while the fungal community structure was mainly affected by the changes in biomass， SWC， and BD. ⑤ The results of redundancy analysis showed that the plant evenness index was the key factor driving the rhizosphere bacterial community of the alpine meadow in the source area of the Yellow River. BD was the main driving factor to change the rhizosphere fungal community of the alpine meadow in the source region of the Yellow River. These findings emphasized the importance of microtopography in driving the diversity， community structure， functional contour， and co-occurrence network of bacteria and fungi in the alpine meadow ecosystem. ⑥ The function prediction of soil bacteria FAPROTAX showed that chemoheterotrophy and aerobic_chemoheterotrophy had the strongest functions in three types of topographic habitats， and at the same time， their functional expression in sunny and floodplain habitats was higher than that in shady habitats （> 5 500）. Fungal FUNGuild function prediction showed that the nutritional types of fungi in the three terrain habitats were different， and compared with that in the sunny slope habitats， the floodplain habitats could increase the abundance of endophytic-litter saprophytic-soil saprophytic-undefined saprophytic fungi. To summarize， topography and habitat are the key driving factors that affect the diversity pattern， community construction， functional characteristics， and symbiotic interaction of soil bacteria and fungi in the alpine meadow ecosystem in the source region of the Yellow River.