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

Abstract

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.

Fungal Methane Production Controlled by Oxygen Levels and Temperature

“…This observation aligns with prior studies indicating that the growth and wood decay activities of saprotrophic fungi diminish when O2 levels fall below 1.5% and 10% or 1%, respectively, and CO2 levels rise accordingly [29,32]. Contrarily, [31] found that xylothrophic basidiomycetes could completely exhaust O2 in their environment and withstand high CO2 levels, even up to 100%. These fungi are, therefore, facultative anaerobes that produce CO2 in O2-deprived environments.…”

“…However, the influence of key parameters like O2 availability and temperature on fungal CH4 formation has not been investigated, even though these factors strongly influence the physiological activity and growth of fungi. Studies have shown that the activity and growth of xylothrophic fungi depend on prevailing O2 mixing ratios [29][30][31]. For instance, xylothrophic fungi, which include the two investigated fungi in this study, can consume all available O2 in their woody habitat and still grow under anoxic conditions [31].…”

“…Studies have shown that the activity and growth of xylothrophic fungi depend on prevailing O2 mixing ratios [29][30][31]. For instance, xylothrophic fungi, which include the two investigated fungi in this study, can consume all available O2 in their woody habitat and still grow under anoxic conditions [31]. On the other hand, studies have indicated that below a concentration of 0.2% O2, fungal growth is completely inhibited [29,30], while the decay of wood debris by saprotrophic fungi decreased with decreasing O2 and increasing CO2 mixing ratios, and vice versa [29,32].…”

Fungal Methane Production Controlled by Oxygen Levels and Temperature

“…However, the influence of key parameters like O 2 availability and temperature on fungal CH 4 formation has not been investigated, even though these factors strongly influence the physiological activity and growth of fungi. Studies have shown that the activity and growth of xylotrophic fungi depend on prevailing O 2 mixing ratios [29][30][31]. For instance, xylothrophic fungi, which include the two investigated fungi in this study, can consume all available O 2 in their woody habitat and still grow under anoxic conditions [31].…”

The Specific and Total CO2 Emission Activity of Wood-Decaying Fungi and their Response to Increase in Temperature

“…The main role in the decomposition of debris in forests of temperate latitudes is played by xylotrophic fungi − Basidiomycota, Agaricomycetes [7][8][9][10]. This is, perhaps, the only group of organisms in the modern biosphere that has a unique set of interconnected ecological and physiological adaptations to the woody habitat and is capable of decomposing the lignocellulosic complex of wood [11]. They determine the main parameters of CO2 emission activity of woody debris and this makes them one of the globally significant regulators of the gas composition of the atmosphere [12], factors of climate stability and change [5].…”