Temperature Sensitivity of CO2 and CH4 Fluxes from Coarse Woody Debris in Northern Boreal Forests

Abstract

Carbon dioxide (CO2) and methane (CH4) are recognized as the main greenhouse gases causing climate warming. In forest ecosystems, the death of trees leads to the formation of coarse woody debris (CWD) that is one of the sources of greenhouse gas emissions due to wood decomposition. We quantified the CO2 and CH4 fluxes from CWD of larch (Larix gmelinii (Rupr.)) and birch (Betula tortuosa Ledeb.) collected in the northern boreal forests of Central Siberia. The CWD samples were incubated at +5, +15 and +25 °C. The CO2 and CH4 fluxes showed strong correlations with temperature, moisture, decomposition stage and the type of wood’s rot. The temperature coefficient Q10 indicated higher temperature sensitivity of CO2 flux within the temperature interval from +5 to +15 °C than from +15 to +25 °C. Methane flux had higher temperature sensitivity within the interval from +15 to +25 °C. It was found that, in boreal forests, CWD of early decay stage can serve as a source of methane to the atmosphere when air temperatures increased above +15 °C. Strong positive correlation between CH4 production and CO2 emission indicated a biological source and supported findings on aerobic origin of the main process contributing to the CH4 flux from decomposing CWD.

Emission of CO2 and CH4 From 13 Deadwood Tree Species Is Linked to Tree Species Identity and Management Intensity in Forest and Grassland Habitats

“…Another indication that CH 4 production and decomposition activity are linked to each other was the positive correlation between CH 4 and CO 2 emission rates (Supplementary Figure S6 in Supporting Information S1), which was also reported by Mukhortova et al. (2021). Therefore, CH 4 emission rates provide rather supplementing information and are not a reliable predictor for deadwood decomposition processes.…”

“…Accordingly, it can be assumed that the decomposition of our sterilized deadwood specimens on forest and grassland soils was mainly determined by aerobic processes, which were only partially accompanied by methanogenic decomposition processes. Another indication that CH 4 production and decomposition activity are linked to each other was the positive correlation between CH 4 and CO 2 emission rates (Supplementary Figure S6 in Supporting Information S1), which was also reported by Mukhortova et al (2021). Therefore, CH 4 emission rates provide rather supplementing information and are not a reliable predictor for deadwood decomposition processes.…”

“…Studies of deadwood emission rates have focused primarily on CO 2 emissions and less attention has been paid to methane (CH 4 ) emissions (Covey & Megonigal, 2019). Interestingly, two different studies observed a positive correlation of both gas emission rates during decomposition indicating deadwood as a biological source for CH 4 emission (Mukhin & Voronin, 2009;Mukhortova et al, 2021). CH 4 emission rates from deadwood can originate from anaerobic microbial decomposition by methanogens (Covey et al, 2012;Hietala et al, 2015) and are attributed to oxygen-depleted habitat conditions, which can be found in the inner parts of wood.…”

Carbon and Oxygen Gas Exchange in Woody Debris: The Process and Climate-Related Drivers

“…That is the rationale for intensive studies of WD decomposition and gas exchange. Although performed in numerous areas, previous research mainly focused on CO 2emission activity of WD and its relevance to climate [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The results of these studies clearly confirm that humidity and temperature are the most important climatic drivers of CO 2 gas exchange in WD and climate change that are projected to increase precipitation and temperature [19], which should significantly affect WD carbon respiration.…”

“…They include not only aerobic but also anaerobic microorganisms, so far as anaerobic conditions could locally form in timber owing to high moisture and O 2 uptake by fungi uncompensated by diffusion. Such conditions promote the formation of anaerobic bacteria and archaea, as well as the anaerobic production of CO 2 and CH 4 as gas exchange [1,4,18,20,35]. There is evidence that methane may also be produced by xylotrophic Basidiomycetes [36,37], many of which can exist in oxygen-free environments [25,38], being de facto electively anaerobic organisms.…”