Methane emission from living tree wood

Abstract

The time courses of CO2, CH4, and H2 accumulation and O2 absorption at the exposure of trunk wood samples taken from living trees of birch (Betula pendula Roth.), bird cherry tree (Padus avium Mill.), and pine (Pinus sylvestris L.) in the closed volume were studied. The activity of these processes at different temperatures (from 5 to 55°C) was also examined. The main components of gas exchange in all three tree species were O2 absorption and CO2 evolution. The fluxes of these gases were equal. In experiments with dehydration-hydration of wood samples, the intrawood origin of “woody” methane was established. Emission of CH4 and H2 from the wood depended on temperature. The temperature dependence of CH4 emission was similar to the temperature dependence of wood respiration. The high correlation between CO2, CH4, and H2 release and O2 absorption was noted. The relationships between these gas-exchange parameters were not species-specific. Temperature maxima of CH4 emission and the respiratory activity coincided. This implies that the highest methane emission should be expected in the period of the growth season most favorable for tree physiology. For the wood from all tree species, the ratio between released CH4 and CO2 volumes was close to 1: 160. This means that the annual methane emission from living tree is about 2 Mt C, attaining 4% of total methane emission from the territory of North Eurasia. However, taking into account a temperature dependence of methane exchange between the vegetation cover and atmosphere, we can expect that, at global climate warming, methane emission volume might be substantial.