Epiphytic lichens are integral to boreal forest ecosystems, yet their allelopathic interactions with host trees, particularly in cryolithozone regions, remain poorly understood. This study elucidates the physiological and biochemical impacts of the epiphytic lichen Physcia alnophila on Larix gmelinii (Gmelin larch), a keystone species in Siberian permafrost forests. By combining dendrochronology, GC–MS metabolomic analysis, and HPLC–ESI–MS/MS analysis, we demonstrate that the lichen’s primary metabolite, atranorin (ATR), systemically migrates from thalli into the host’s cambium, roots, and needles, with root accumulation reaching 36.3 µg g⁻¹ DW. Lichen-colonized trees exhibited severe radial growth inhibition (27%–51% reduction over five years) and suppressed apical growth, despite comparable heights to controls, indicating chronic phytotoxicity. Metabolomic profiling revealed lichen-specific polyols (e.g., arabitol, mannitol) in larch tissues, alongside elevated stress biomarkers (terpenes, sterols, phenolic acids), and significant disruptions to the tricarboxylic acid cycle and oxidative phosphorylation. These metabolic perturbations correlate with reduced monosaccharide availability and impaired energy production, directly linking ATR translocation to growth suppression. L. gmelinii exhibited compensatory responses, including increased fatty acids and arabinogalactan synthesis, suggesting adaptive mechanisms to mitigate lichen-induced stress. Our findings suggest P. alnophila as a biotic stressor that affects tree physiology in extreme climates, with implications for boreal forest resilience. This work provides an insight to the rarely pointed out species interactions, which, when combined with climate change, may alter carbon cycling and forest dynamics in permafrost ecosystems.

Epiphytic lichens are naturally subjected to highly fluctuating light and must protect their algal symbionts from harmful short wavelengths while facilitating efficient photosynthesis. Confocal microscopy confirmed that the upper cortices of Hypogymnia physodes and H. bitteri thalli contained colorless secondary metabolites atranorin and chloroatranorin, which were able to protect lichens against excessive UV and blue–violet radiation in two ways. The first way screens algae through visible light reflection; the second way is realized through the absorption of UV-A and blue–violet radiation and fluorescence emission in the yellow–green spectrum. Acetone rinsing removed atranorin and chloroatranorin crystals from the cortical surface, thus reducing the reflectance of both H. physodes and H. bitteri. Nevertheless, fluorescence in H. physodes remained largely unaffected due to the deep-layer localization of atranorin within the upper cortex. However, melanized H. bitteri exhibited weak fluorescence either before or after acetone rinsing, despite containing atranorin and chloroatranorin at levels comparable to H. physodes. Within the heavily melanized lower cortical layer of H. bitteri, young areas contained significant amounts of atranorin and chloroatranorin. A reduction in their content resulted in a compensatory enhancement of non-photochemical quenching in algae. This phenomenon suggests that atranorin and chloroatranorin contribute to the photoprotection of lichens in yet another way through light reflectance and through fluorescence in a photosynthetically safe manner.

Prokopiev, I., Zholobova, Zh., Himelbrant, D. & Frolova, D. 2026. Das gelbe Pigment Subauriferin aus Melanelixia subaurifera und seine Identität mit Secalonsäure A. – Herzogia 39: 280 – 283. Die Struktur eines schwefelgelben Pigments aus der Flechte Melanelixia subaurifera, historisch als Subauriferin bezeichnet, wurde aufgeklärt. Chromatographische Analysen von Flechtenextrakten zeigten, dass diese Verbindung hinsichtlich Molekulargewicht und UV-Spektrum mit Secalonsäure A, einem bekannten gelben Pigment, das sowohl in lichenisierten als auch in nicht-lichenisierten Pilzen vorkommt, übereinstimmt. Myelochroa entotheiochroa und Pseudoparmelia cubensis, die für ihren hohen Gehalt an Secalonsäure A bekannt sind, wurden als Referenzproben ausgewählt. Ein Vergleich der chromatographischen und spektrometrischen Daten von Secalonsäure A und des Pigments Subauriferin bestätigte deren Identität.