Mycorrhizal associations of the exotic hickory trees, Carya laciniosa and Carya cordiformis, grown in Kórnik Arboretum in Poland

We studied mycorrhizal associations of North American Carya laciniosa and Carya cordiformis trees, successfully acclimated to local habitat conditions of the historic Kórnik Arboretum in Poland, in order to better understand mycorrhizal host range extensions in new environments. The root systems of Carya seedlings (1-3 years old), regenerated under a canopy of mature hickory trees, were analyzed using microscopic, morphological, and molecular techniques. Our results, for the first time, indicate that C. laciniosa and C. cordiformis have both arbuscular and ectomycorrhizal associations. In the cleared and stained roots of both Carya species, typical structures of arbuscular mycorrhizae (vesicles, arbuscules, hyphal coils, and intercellular nonseptate hyphae) were detected. On the basis of ITS rDNA sequencing, 40 ectomycorrhizal fungal taxa were revealed, with 25 on C. laciniosa and 19 on C. cordiformis. Only four fungal species (Cenococcum geophilum sensu lato, Russula recondita, Xerocomellus cisalpinus, Humaria hemisphaerica) were shared by both Carya species. The high number of infrequent fungal taxa found, as well as the calculated richness estimator, indicates that the real ectomycorrhizal community of C. laciniosa and C. cordiformis is probably richer. The ability of the exotic Carya species to form arbuscular and ectomycorrhizal linkages with native fungi could be a factor in the successful establishment of these tree species under the conditions of Kórnik Arboretum.