Objective To explore the composition and assembly process of soil fungal communities in Pinus sylvestris var. mongolica plantations of different ages in the Mu Us Sandy Land, Shaanxi Province of northwestern China and to reveal the effects of stand age on composition and function of soil fungi.

Method Soil samples were collected associated with 26, 32, 43 years old P. sylvestris var. mongolica plantations in the Mu Us Desert to identify and analyze the composition, diversity, assembly and function of soil fungal communities based on field investigation, Illumina Miseq high-throughput, iCAMP and FUNGuild platform.

Result (1) No significant difference in the α diversity or β diversity of soil fungal communities was detected for P. sylvestris var. mongolica with stand aging (P > 0.05). A total of 285 genera of soil fungi from 5 phylums, 23 phylums, 62 orders, 133 families were obtained, and the highest relative abundance of soil fungi of different forest ages were all from Inocybe. With the increase in forest age, the relative abundance of Genabea, Pulvinula and Sphaerosporella increased significantly. (2) In soil fungi, in addition to other trophic types, symbiotic trophic types dominated, followed by saprophytic trophic types. There was a significant increase in relative abundance of symbiotic fungi (P < 0.05), and the saprotrophic fungi decreased significantly (P < 0.05) with increasing forest age. No significant correlation (P > 0.05) was found between soil physical and chemical properties and soil fungal functions. The community assembly process of soil fungi in P. sylvestris var. mongolica plantations of different forest ages was mainly dominated by diffusion limitation.

Conclusion In Pinus sylvestris var. mongolica plantations of the Mu Us Sandy Land, as forest age increases, the soil fungal community structure becomes more similar and stable. The function of soil fungi is more favorable to tree growth. The community assembly is mainly influenced by fungal birth, death, migration and emigration,