Abstract. Although the dynamics of methane (CH 4 ) emission from croplands and wetlands have been fairly well investigated, the contribution of trees to global CH 4 emission and the mechanisms of tree transport are relatively unknown. CH 4 emissions from the common wetland tree species Populus trichocarpa (black cottonwood) native to the Pacific Northwest were measured under hydroponic conditions in order to separate plant transport mechanisms from the influence of soil processes. Roots were exposed to CH 4 enriched water and canopy emissions of CH 4 were measured. The average flux for 34 trials (at temper-
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