Lichens are globally widespread organisms playing an important role in diverse ecosystems. They produce secondary metabolites, unique compounds, which play many important ecological and biological roles, including their effects on other plants, through allelopathy.

Many of them also inhibit the growth of higher plants (1). Brown and Mikola (2) mentioned negative lichen allelopathy effects on the germination and development of conifer trees, whereas Stark and Hyvarinen (3) and Kytoviita and Stark (4) documented neutral, no allelopathic effect of lichens on conifer trees. On the other hand, the negative influence was achieved when the plant species naturally not co-occurring with lichens were laboratory treated with usnic acid, one of the lichen secondary metabolite. Such species include tomato (5), wheat and sunflower (6) and red clover (7). Lichen secondary metabolites are soluble the most in organic solvents.  However, aqueous extracts of certain lichens species possessed cytotoxicity effects on meristematic cells of lettuce and maize (8). Particularly H. physodes synthesize depsidones and depsides, such as protocetraric acid, physodalic acid and atranorin (9).   

Our aim was to measure total germination of Picea abies, Pinus sylvestris and Pinus mugo in the presence of aqueous lichen extracts. The extracts were made from lichens (Hypogymnia physodes, Parmelia sulcata, Physcia adscendens, Pseudevernia furfuracea) collected from fallen branches. For experiment we macerated dried lichens  for 24 (1 day) and 72 hours (3 day) in rain water (1:10 mg/ml). We analysed total anion and cation content and pH in rain water and extracts. Besides we monitored secondary metabolites and sugars soluted in the extracts by HPLC. 

We conclude that aqueous lichen extracts from particular species naturally growing on trees can be considered as a source of nutrients for young emerging conifers from the same habitat. The extracts contained much more anions and cations than pure rain water. Assumpted low solubility (10) of lichen secondary metabolites and sugars in water was confirmed. Our observations show that P. sylvestris is more sensitive than P. mugo and P. abies. Only 3 day extract, which contained the greatest amount of nutrients, significantly (P < 0.05) stimulated germination of P. sylvestris and therefore overtook possible negative allelopathy effect showed by 1 day extract treatment

This work was supported by the Slovak Grant Agency (KEGA 012UPJŠ-4/2016 and VEGA 1/0792/16).

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