Abstract
The terricolous species Cladonia foliacea (Cladoniaceae, lichenised Ascomycota) widely distributed in open, dry lowland steppe and rocky mountain grassland vegetation in Europe was chosen as a potential test organism for ecological experiments, since their thalli are producing cortical solar radiation-protective and UV screening pigment dibenzofuran usnic acid and medullary secondary substance depsidone fumarprotocetraric acid. Significant seasonal differences were found in the amounts of lichen secondary metabolites analysed by HPTLC and HPLC-PDA between summer and winter collected thalli in sandy grassland area in Hungary. The concentrations of usnic acid varied between 7.34 and 15.52 mg/g in summer collected samples and 13.90 and 21.61 mg/g in winter collected ones. A comparable amount (11.61±0.29 mg/g) was measured in pulverised samples. The concentrations of fumarprotocetraric acid varied between 0.60 and 3.01 mg/g in summer collected samples and 2.26 and 5.81 mg/g in winter collected thalli. A comparable amount (2.45±0.21 mg/g) was found in pulverised samples. The range of concentration values is comparable with data known from lichens. A higher amount of usnic acid is produced in winter probably to ensure sufficient protection also for summer. The fumarprotocetraric acid content of the medulla might contribute to the solar irradiation reflecting role of the pale lower surface lobes turning upwards in dry condition.
Highlights
Lichenised associations represent a sensitive model ecosystem for investigating various or changed environmental conditions
Lichens produce a great variety of lichen secondary metabolites (LSMs), and most of them are unique to lichen-forming fungi as it is summarised in recent reviews on their biological roles (Calcott et al 2018, Molnár and Farkas 2010)
Collected samples were checked for presence of usnic acid and fumarprotocetraric acid by high performance thin layer chromatography (HPTLC) according to standard methods for analysing lichen samples described by Arup et al (1993) and Molnár and Farkas (2011)
Summary
Lichenised associations represent a sensitive model ecosystem for investigating various or changed environmental conditions (cf. Asplund et al 2017, Bergamini et al 2005, Galloway 1993, Nash 2008, Stofer et al 2006). 1,050 secondary compounds have been identified to date (Stocker-Wörgötter 2008, 2015) These chemically diverse (aliphatic and aromatic) lichen substances are produced by the mycobiont (Elix 1996, Huneck 1999). The lichen species Cladonia foliacea is a frequent chlorolichen in open, dry, sun-exposed habitats in the Hungarian lowland steppe areas as well as in low mountain rocky grasslands. Since it has a great potential in experimental applications, it was selected for a test organism and tested for its tolerance for acetone treatment (Farkas et al 2020). Our present aim was to check LSM content of exactly the same thalli by the analysis of the soaking acetone-solution, to study seasonal differences in samples collected in two seasons, summer and winter
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