Abstract
The carbon-to-oxygen relationship and gas exchange balance, organic carbon to CO2 conversion intensity and efficiency, and their relevance to climate parameters and wood decay fungi were investigated for birch woody debris (WD) in the Mid-Urals mixed pine and birch forests. It was shown that, within the range of temperatures from 10 to 40 °C and relative moisture (RM) of wood of 40% and 70%, aerobic gas exchange was observed in the WD, encompassing the physiologically entwined processes of CO2 emission and O2 uptake. Their volumetric ratio (0.9) confirmed that (1) the WD represents a globally significant CO2 source and appropriate O2 consumer and (2) the oxidative conversion of organic carbon is highly efficient in the WD, with an average ratio of CO2 released to O2 consumed equal to 90%. The balance of carbon-to-oxygen gas exchange and oxidizing conversion efficiency in the WD were not affected by either fungal species tested or by moisture or temperature. However, the intensity of gas exchange was unique for each wood decay fungi, and it could be treated as a climate-reliant parameter driven by temperature (Q10 = 2.0–2.1) and moisture (the latter induced a corresponding trend and value changes in CO2 emission and O2 uptake). Depending on the direction and degree of the change in temperature and moisture, their combined effect on the intensity of gas exchange led to its strengthening or weakening; otherwise, it was stabilized. Aerobic respiration of wood decay Basidiomycetes is an essential prerequisite and the major biotic factor in the WD gas exchange, while moisture and temperature are its climatic controllers only.
Highlights
Introduction iationsForests are the largest terrestrial carbon sinks and reservoirs, playing an important role in CO2 regulation in the atmosphere
This was confirmed by the close correlation factors derived for O2 and CO2 fluxes under similar temperatures but different relative moisture (RM) (40% and 70%): They were 0.88 and 0.96 for +10 ◦ C, 0.93 and 0.97 for +20 ◦ C, 0.91 and 0.84 for +30 ◦ C, and 0.96 and 0.93 for +40 ◦ C, correspondingly (Figure 1)
A similar positive correlation was found for CO2 and O2 fluxes and gas exchange in wood affected by white (Fomes fomentarius) and brown (Fomitopsis betulina) rot: The values of the factors were 0.79–0.85 and 0.84–0.82 for wood with RM 40% and 70%, correspondingly (Figure A1)
Summary
Forests are the largest terrestrial carbon sinks and reservoirs, playing an important role in CO2 regulation in the atmosphere. Their carbon cycle is specified by a large-scale and long-lasting (from dozens to hundreds of years) woody pool. It is estimated at 30 Gt C for the forests of Russia, and 240 Mt are annually added to it. Mobilization of woody pool carbon, shown by biological decomposition of woody debris (WD), is the main process of the forest ecosystem carbon cycle. That is the rationale for intensive studies of WD decomposition and gas exchange
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