Anatomical, Morphological, and Physiological Features of Cyanolichen Peltigera praetextata (Florke ex Sommerf.) Zopf Thalli in Different Ontogenetic States

The goal of this study is to describe the cyanolichen Peltigera praetextata ontogenesis stages and reveal some of their morphological, anatomical, and physiological features. This paper analyzes 300 P. praetextata thalli taken in 2019 from aspen trunks in the aspen-spruce communities of the middle taiga territory in Kivach Nature Reserve (62°15'15.9'N, 33°58'746.1"E) from permanent sample plots. The authors determined the ontogenetic state of each thallus based on morphology and anatomy data using the concept of a discrete approach to the description of ontogenesis (Suetina, 2001). They registered the following thalli parameters: length, width, presence and length of rhizines, presence and width of veins, presence of phyllidia and apothecia, number of notches and lobes, shape, edge curl, and surface tomentum. They studied the anatomical parameters (thallus total thickness, tomentum thickness, cortical layer, algal layer and medulla thickness, algae cell size) using sections of thalli samples in all ontogenetic states from the apical, medial, and basal parts in triplicate. They measured the content of photosynthetic pigments spectrophotometrically with preparation of alcoholic extracts. To assess the parameters of the water regime of thalli having different ontogenetic states, the authors calculated a specific thallus mass (STM) and water holding capacity (WHC). They made a statistical data measurement using one-way ANOVA and regression analysis. They also calculated the coefficient of variation (CV) to assess the variability of the features under study. The study identified four periods and 12 ontogenetic states of P. praetextata: latent (sp), pre-generative (pr, prt, j, iml, im2, im3, vl, v2), generative (g), and post-generative (ss, s). The values of the morphological and anatomical parameters of the thalli increase during their development. The early ontogenesis stages demonstrate the highest variability of the parameters. The highest variability of the thallus structures under study within the ontogenetic states is registered for the rhizine length, vein width, and medulla thickness, while the highest constancy is typical of the share of the algal layer in the thallus that varies within a very limited range (22-32%) and reaches the minimum values in the post-generative period. The mycobiont increases in volume through a medulla growth. The physiological characteristics of the P. praetextata thalli differ in various ontogenetic states, while the generative thalli characterized by a normal ratio of photosynthetic pigments, maximum water saturation, and maximum water holding capacity have the maximum values. Thus, at early development stages, the thalli demonstrate a lower ability to retain moisture and may represent a critical stage in a lichen life cycle. On the one hand, the revealed wide variability of the morphological and anatomical parameters of young thalli testifies to their high adaptability, but the physiological parameters of water saturation indicate the vulnerability of these stages. These parameters confirm the validity of the ontogenetic stages identified. The paper contains 5 Figures, 5 Tables and 55 References. The Authors declare no conflict of interest.

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