RESUMEN
The question of the nature of the interaction between epiphytic lichens and their host trees remains highly debated. Some authors showed cases of allelopathy, but this needs further investigation. Our study covers the effects caused by the epiphytic lichen Evernia esorediosa (Müll. Arg.) Du Rietz on growth and biochemical processes in Larix gmelinii (Rupr.) Rupr. ex Kuzen trees in cryolithozone boreal forests. Usnic acid (UA) is shown to migrate from the thalli of E. esorediosa in the bark and phloem of L. gmelinii, from which it is transported to the root system of the tree, and then UA is moved upward through the xylem into tree needles. Accumulation of UA in L. gmelinii needles causes the following effects: inhibition of photosynthesis, cellular respiration and oxidative phosphorylation. These disruptions could reflect on the tree growth processes. The L. gmelinii trees inhabited by the epiphytic lichen E. esorediosa were found to show lower radial and apical growth parameters. Our results show that E. esorediosa exhibits an allelopathic effect toward L. gmelinii through the migration of UA from the lichen thalli to the tissues of the tree, which led to inhibition of energetic processes in cells. This caused the tree growth to slow down and could ultimately lead to its death.