Foliar fungal communities of naturally regenerated and nursery-produced Scots pine (Pinus sylvestris) seedlings

Abstract: Endophytic fungal communities living in leaves of trees can have a significant impact on their hosts,showing both beneficial and detrimental effects. Some mutualistic fungal species protect the host against pathogens or herbivores, while pathogenic species can increase the vulnerability of the host against biotic and abiotic stresses. The Swedish forestry model consists of planting nursery-produced seedlings after final felling. In the nurseries, the seedlings are grown densely in containers under greenhouse conditions and for disease prevention the Integrated Pest Management strategy is followed, where fungicides are applied to protect the plants. It is known that the intensive nursery production system affect the fungal communities present in the roots of seedlings by making them less diverse, but the effect in the foliar fungi is still unknown. The main objective of this study was to investigate the diversity of foliar fungal communities in Scots pine (Pinus sylvestris) seedlings produced in the nursery after their transplantation to the forest clear-cuts and to compare them with naturally regenerated seedlings. Needle samples of both types of seedlings were collected from three different forest clear-cut sites in Uppland, Sweden. The time scale and the exposure time of the needle were taken into account by sampling at 8-time points of the seasonal period and taking one-year old needles and current-year needles. Fungal communities were characterised by high- throughput sequencing of the ITS2 rRNA region of healthy-looking needles. Sequences were filtered and grouped into operational taxonomic units (OTU). The taxonomic classification of each OTU was determined using the PROTAX-fungi and massBLASTer databases and fungal lifestyle was assigned using the FungalTraits database. Results show that exposure time and needle age are the main factors affecting fungal diversity in needles, irrespective of whether seedlings are from nurseries or natural regeneration. Overall, fungal communities on needles of Scots pine are similar at different sites. The needle mycobiome was dominated by a fungal species belonging to the family Pseudeurotiaceae (10%), a species of the genus Cladosporium (9%), the species Sydowia polyspora (4%) and a species of the family Herpotrichiellaceae (2%). Further studies should focus on how colonisation of new needles develops in nursery-produced seedlings and compare this with naturally regenerated seedlings.