Biogeochemical and anatomical studies on the mechanisms of tree-mediated methane emissions in forested wetland ecosystems

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We performed field measurements of CH4 fluxes at tree stems to clarify the major controlling factors of stem CH4 emission rates in cool-temperate forested wetlands. We also conducted anatomical observations of wood structure of tree roots in relation to the possible transport pathway of soil-borne CH4 in a tree body.CH4 emission rates from stems of mature Fraxinus mandshurica trees varied greatly among individuals within a study site (0.12ha), and showed a spatial gradient apparently corresponding to the difference in water table depth in the site. Large inter-individual differences were also observed in the magnitude of seasonal changes in stem CH4 emission rate. CH4 emission rates were quite stable throughout a 24 h period for foliated trees and similarly for defoliated trees. Well-developed lysigenous intercellular spaces, i.e., aerenchyma tissues, were observed at the cortex of fine roots of mature Fraxinus mandshurica trees.