Woody stem methane emission in mature wetland alder trees

Copyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyright owners. For more information on Open Research Online's data policy on reuse of materials please consult the policies page. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Abstract 33 34 Methane (CH 4) is an important greenhouse gas that is predominantly emitted to the 35 atmosphere from anoxic wetland ecosystems. Understanding the sources and emissions of 36 CH 4 is crucially important for climate change predictions; however, there are significant 37 discrepancies between CH 4 source estimates derived via so-called bottom-up and top-down 38 methods. Here we report CH 4 emission from the stems of mature wetland alder (Alnus 39 glutinosa) trees in the UK, a common tree of northern hemisphere floodplains and wetlands. 40 The alder stems most likely behave as conduits for soil-produced CH 4 either in the gaseous or 41 aqueous phase, and may, therefore, help to reconcile methodological differences in the way 42 the wetland CH 4 source is estimated. 43 Alder tree stems emitted average peak CH 4 fluxes of 101 µg CH 4 m-2 hr-1 (on a stem 44 area basis) in early October, a rate that is similar to that obtained from mature Japanese ash 45 (Fraxinus mandshurica var. japonica) in Japan and amounting to approximately 20% of the 46 measured CH 4 flux from the soil surface. The finding suggests that trees, which occupy 60% 47 of Earth's wetlands and are normally excluded from the measurement programmes that form 48 the basis for bottom-up estimates of the global wetland source, could be important 49 contributors to overall terrestrial ecosystem CH 4 flux. Introduction 51 Wetlands form the largest source of methane (CH 4) to the atmosphere, a powerful greenhouse 52 gas that is thought to have contributed approximately 50% of the enhanced greenhouse effect 53 of CO 2 since 1850 (Hansen et al., 2000). Great importance is therefore placed on 54 characterizing the various CH …