Plant-microbe interactions are fundamental to biodiversity maintenance and ecosystem functioning, and their assembly is shaped by a complex interplay of ecological and evolutionary processes. However, how these forces jointly influence ectomycorrhizal (EcM) fungal communities, especially those dominant in subalpine forests, remains poorly understood. To address this, we investigated EcM fungal communities associated with 11 species of Pinaceae (Abies, Picea, and Pinus) across 195 monodominant stands in the subalpine forests of the Qinghai-Tibetan Plateau. We found that all pine species consistently associated with a broad phylogenetic range of EcM fungal lineages and that pine-EcM association networks exhibited low connectance, indicating low partner specificity. Variation in fungal community structure was significantly influenced by host identity, environmental factors, and spatial distribution, but not by host phylogenetic relatedness. Notably, fungal taxa from three dominant lineages (Sebacina, Russula, and Inocybe) were clustered phylogenetically with globally distributed Pinaceae-associated taxa, pointing to evolutionarily conserved symbiotic associations across biogeographic regions. Together, these results indicate that EcM fungal communities in subalpine Pinaceae forests are assembled through a combination of evolutionary conservatism and environmental filtering. The persistent association with key EcM fungi across Pinaceae species underscores their essential role in supporting tree physiology and forest ecosystem stability in subalpine environments.