Ecological and physiological studies of photosynthesis and associated processes in lichens (review)

Lichens are the oldest symbiotic organisms. Their thallus represents a structure created by a mycobiont for a population of photobiont cells, the presence of which transforms a fungal heterotrophic organism into an autotrophic association. The review article summarizes the results of ecological and physiological studies of lichens in the taiga zone on the European North-East of Russia. The data on the photosynthetic activity, the effects of environmental factors on the thallus photosynthesis, and the reactions aimed at fine-tuning the functional structure and metabolism of lichens to habitat conditions are presented and analyzed. The importance of the photobiont type for the functioning of the entire lichen association is demonstrated. Cyanobiont lichens were found to be characterized by a higher nitrogen content and intensive metabolism, compared with chlorobionts. In most of the studied lichen species, the content of chlorophyll a varied within 0.4-0.8 mg/g of the dry mass of thallus, and the concentration of carotenoids was by 2.5-3 times as less. The maximum net uptake of CO2 in lichens was observed at a temperature of 15-20 °C and a relative water content of about 60 %. The saturation of photosynthesis with light was noted at a photosynthetic photon flux density being by four-five times less than that of the total solar radiation. The effects of exposure of thalli to UV radiation and environmental pollution with bauxite dust have been revealed. Promising directions for further research are outlined.