Fungal endophytic communities within the microbiome of birch leaves respond to elevated radiation at the Chornobyl Exclusion Zone

How symbiotic interactions evolve under continuous radiation, is unknown. We compared epiphytic, living on surfaces, and endophytic, living in plant tissues, microbial communities of birch leaves at the Chornobyl Exclusion Zone (CEZ), to evaluate the effect of elevated radiation between the two levels of intimacy. The most common endophytic fungi belonged to the genus Microstroma , and Taphrina spp. dominated epiphytic fungi. Pseudomonas was a birch shoot-specific bacterial endophyte. Composition of microbial communities was mainly dependent on location, but radiation significantly affected the structure of endophytic fungal communities. In Red Forest with highest radiation levels, Coniozyma was most frequent, and Venturia pyrina was identified as a core taxon. Both of these endophytic fungi are melanized and tolerate stressful environments. Endophytic bacterial communities of Red Forest hosted insect endosymbionts, suggesting that trees were exposed to herbivory. The endo- and epiphytic communities also resembled each other in Red Forest, indicating a weakened defense system. Our data shows that prolonged radiation alters the most intimate symbiotic communities of trees.