Host phylogenetic relatedness and soil nutrients shape ectomycorrhizal community composition in native and exotic pine plantations

Exotic non-native Pinus species have been widely planted or become naturalized in many parts of the world. Pines rely on ectomycorrhizal (ECM) fungi mutualisms to overcome barriers to establishment, yet the degree to which host specificity and edaphic preferences influence ECM community composition remains poorly understood. In this study, we used high-throughput sequencing coupled with soil analyses to investigate the effect of host plant identity, spatial distance and edaphic factors on ECM community composition in young (30-year-old) native (Pinus massoniana Lamb.) and exotic (Pinus elliottii Engelm.) pine plantations in China. The ECM fungal communities comprised 43 species with the majority belonging to the Thelephoraceae and Russulaceae. Most species were found associated with both host trees while certain native ECM taxa (Suillus) showed host specificity to the native P. massoniana. ECM fungi that are known to occur exclusively with Pinus (e.g., Rhizopogon) were uncommon. We found no significant effect of host identity on ECM communities, i.e., phylogenetically related pines shared similar ECM fungal communities. Instead, ECM fungal community composition was strongly influenced by site-specific abiotic factors and dispersal. These findings reinforce the idea that taxonomic relatedness might be a factor promoting ECM colonization in exotic pines but that shifts in ECM communities may also be context-dependent.