Endophytic fungal communities in the needles of Scots Pine, Pinus sylvestris, planted in three progeny plantations in Scotland

Forest tree species are challenged by changes in the environment at an increasing rate. Among others impacts of Climate Change and emerging tree diseases have received most attention and the interaction between both is seen as a significant threat. From tree breeding to planting- and forest management strategies are being investigated for their ability to increase resilience at tree species- to forest ecosystem levels. Tree - microbial interactions have long been known to be able to support trees with some emphasis on soil fungal mutualists such as mycorrhiza. The foliar microbiomes have received less attention, but are widely seen to have great potential to contribute to tree resilience and resistance to disease.Here we present a study of the endophytic fungal community in the needles of Pinus sylvestris, Scots Pine, as the extended phenotype of the tree in a progeny trial in three location in Scotland. Seed material from 5 provenance zones collected on 8 maternal trees in each. Seedlings were planted in three locations with different predominant climates; in short warm & wet, Inverewe, cold & dry, Glensaugh, and warm & dry, Yair. The endophytic fungal community was recorded by amplicon (ITS2) metabarcoding.Across the three common gardens we characterise the fungal endophyte communities. At a clustering threshold of 97% we recorded 7610 Operational Taxonomic Units (OTUs). After rarefying to account for sequencing depth 2079 OTUs remained varying from 1423 at Glensaugh to 700 at Inverewe. Comparing measures of average OTU richness per tree yielded no difference between the three locations nor did they correlate with climate variables at the sites of origin of the seed material. Shannon diversity was lowest at Glensaugh, which also showed the most uneven frequency distribution with the genus Lophodermium representing 56.8% of the reads. Partitioning the variance in community structure between location, provenance and family using multivariate general linear modelling shows clearly that family accounts for most of the variance across all taxonomic levels. However, the terms explanatory power is only significant on the basis of abundance, but not presence/absence.Finally we adapt methods to differentiate core (common & abundant) from satellite (infrequent and scarce) species in the endophytic fungal community. Applying them only to species with a full taxonomic match the reference data from UNITE 7.0 we identify 120 out of 600 species as comprising the core. Results are discussed in the context of likely ways of community assembly, but also the potential of managing tree microbiota to mitigate future challenges.