Selection dictates the distance pattern of similarity in trees and soil fungi across forest ecosystems

How the four major processes affecting community assembly—selection, dispersal, drift, and diversification—solely or jointly shape co-occurring assemblages of macro- and microorganisms at the same scales remains poorly understood. Here, we delved into the distance pattern of similarity (DPS) in tree and soil fungal communities in three c. 20-hectare forest plots spanning tropical to temperate climates in Yunnan province, Southwest China. Specifically, we decrypted the assembly contribution of individual-based random sampling, selection and/or dispersal using drift-inexplicit ordination and drift-explicit baseline models. Surprisingly, our findings demonstrated that most soil fungal realized distribution ranges (RDR) were shorter than most trees. Because of explicitly integrating drift and the range of DPS is broader than the RDR of most trees and fungi, selection baseline models overwhelmingly captured the DPS structures in trees and fungi across spatial scales in tropical, subtropical, and subalpine forest ecosystems and that for fungi across taxonomic levels and fungal guilds. Under the premise that modeling frameworks, ecosystems, spatial scales, sample intensities, selection variables, and dispersal variables are well unified, the ubiquitous dominance of selection elucidates no fundamental difference in the assembly mechanism between trees and soil fungi.