Eco-Physiological Adaptations of the Xylotrophic Basidiomycetes Fungi to CO2 and O2 Mode in the Woody Habitat

The aim of this research is to study of eco-physiological adaptations of xylotrophic fungi (Basidiomycota, Agaricomycetes) to hypoxia, anoxia and hypercapnia as the main environmental factors that determine the activity of fungi in woody habitat. The study was carried out on seven species of polypore fungi widespread in the preforest-steppe pine-birch forests of the Central Urals, including both white (D. tricolor, D. septentrionalis, F. fomentarius, H. rutilans, T. biforme) and brown (F. betulina, F. pinicola) rot. Their CO₂ and O₂ gas exchange were analyzed in natural samples of woody substrates (Betula pendula, Pinus sylvestris) and basidiocarps by the chamber method using a CO₂/O₂ gas analyzer. It was shown that the intensity of O₂ gas exchange is positively related to the oxygen concentration but is not very sensitive to a decrease in its content in the woody habitat. Xylotrophic fungi are able to completely exhaust the O₂ in the habitat, and this process is linear, indicating that they do not have threshold values for oxygen content. Oxygen consumption is accompanied by an adequate linear increase in CO₂ concentration up to 18-19%. At a concentration of 5-10%, carbon dioxide does not affect the gas exchange of xylotrophic fungi and can even enhance it, but at 20% it significantly reduces its intensity. Xylotrophic fungi are resistant to high CO₂ concentrations and remain viable at 100% CO₂ concentration and are capable of growth under these conditions. In an oxygen-free habitat, anaerobic CO₂ emissions are recorded; when O₂ appears, its consumption is restored to the level preceding anoxia. Xylotrophic fungi are the specialized group of saprotrophic microaerophilic and capnophilic facultative anaerobes adapted to develop at low oxygen and high carbon dioxide concentration, anoxia.