Niche differentiation shapes the community assembly of fungi associated with evergreen trees in the Horqin desert

Fungal communities inhabit plant soil and roots, occupying different niches. Soil fungi (SF) and root-associated fungi (RAF) strongly affect plant health and growth. Owing to the regulation of deterministic and stochastic processes, the community assembly of SF and RAF may exhibit spatiotemporal differences. Moreover, stand age affects the fungal community distribution, soil properties, and the understorey microenvironment in desert forest ecosystems. However, little is known about the underlying mechanisms by which stand age shapes the SF and RAF community assemblies in desert forest ecosystems. Therefore, we collected soil and root samples of Mongolian pine (Pinus sylvestris var. mongolica) from five stands (13a (young), 22a (half-mature), 34a (nearly mature), 41a (mature), and 55a (overmature)) in the Horqin Desert to reveal the community assembly of SF and RAF associated with Mongolian pine plantations. The results indicate that (1) stand age affected the diversity, responsive taxa, and composition of SF rather than those of RAF. (2) RAF communities were more stable than SF communities were, and the community stability of the SF and RAF communities was influenced mainly by symbiotroph_saprotroph fungi and symbiotroph_pathotroph_saprotroph fungi, respectively. (3) Compared with the RAF communities, the SF communities presented wider niche breadth (p < 0.001) and lower niche overlap (p < 0.05). Dispersal limitation (75.33 %) and ecological drift (58.33 %) played crucial roles in controlling the respective SF and RAF community assemblies. (4) The community assembly of the SF and RAF communities was affected mainly by soil moisture and soil nutrients. The response of the SF community composition (p < 0.001) to stand age was stronger than that of the RAF community composition (p < 0.05). The results reveal that stand age had a stronger effect on SF community characteristics and community assembly processes than on those of RAF. These studies help elucidate the differences in fungal communities in different niches of desert ecosystems. Understanding the responses of SF and RAF communities to stand age may improve the understanding of the potentially profound consequences of stand age on microbiome function in desert forest ecosystems.