Abstract

Globally, billions of tons of carbon sequestered in trees are annually recycled back to the atmosphere through wood decomposition by microbes. In Norway, every fifth Norway spruce shows at final harvest infection by pathogenic white-rot fungi in the genera Heterobasidion and Armillaria. As these fungi can mineralize all components of wood, we predicted that they have a significant carbon footprint. Gas samples taken from infected stems were analyzed for CO₂ and CH₄ concentrations, and wood samples from different parts of the decay columns were incubated under hypoxic (4% O₂) and anoxic laboratory conditions. In spring and summer the stem concentrations of CO₂ were generally two times higher in trees with heartwood decay than in healthy trees. For most of the healthy trees and trees with heartwood decay, mean stem concentrations of CH₄ were comparable to ambient air, and only some Armillaria infected trees showed moderately elevated CH₄. Consistently, low CH₄ production potentials were recorded in the laboratory experiment. Up-scaling of CO₂ efflux due to wood decay in living trees suggests that the balance between carbon sequestration and emission may be substantially influenced in stands with high frequency of advanced root and stem heartwood decay. View Full-Text