Wetlands are the largest global source of atmospheric methane (CH4), a potent greenhouse gas. However, methane emission inventories from the Amazon floodplain, the largest natural geographic source of CH4 in the tropics, consistently underestimate the atmospheric burden of CH4 determined via remote sensing and inversion modelling, pointing to a major gap in our understanding of the contribution of these ecosystems to CH4 emissions. Here we report CH4 fluxes from the stems of 2,357 individual Amazonian floodplain trees from 13 locations across the central Amazon basin. We find that escape of soil gas through wetland trees is the dominant source of regional CH4 emissions. Methane fluxes from Amazon tree stems were up to 200 times larger than emissions reported for temperate wet forests and tropical peat swamp forests, representing the largest non-ebullitive wetland fluxes observed. Emissions from trees had an average stable carbon isotope value (δ13C) of −66.2 ± 6.4 per mil, consistent with a soil biogenic origin. We estimate that floodplain trees emit 15.1 ± 1.8 to 21.2 ± 2.5 teragrams of CH4 a year, in addition to the 20.5 ± 5.3 teragrams a year emitted regionally from other sources. Furthermore, we provide a ‘top-down’ regional estimate of CH4 emissions of 42.7 ± 5.6 teragrams of CH4 a year for the Amazon basin, based on regular vertical lower-troposphere CH4 profiles covering the period 2010–2013. We find close agreement between our ‘top-down’ and combined ‘bottom-up’ estimates, indicating that large CH4 emissions from trees adapted to permanent or seasonal inundation can account for the emission source that is required to close the Amazon CH4 budget. Our findings demonstrate the importance of tree stem surfaces in mediating approximately half of all wetland CH4 emissions in the Amazon floodplain, a region that represents up to one-third of the global wetland CH4 source when trees are combined with other emission sources.

中文翻译：

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洪泛区树木的大量排放关闭了亚马逊的甲烷预算

湿地是全球最大的大气甲烷 (CH4) 来源，这是一种强效温室气体。然而，亚马逊洪泛区（热带地区最大的 CH4 自然地理来源）的甲烷排放清单始终低估了通过遥感和反演模型确定的 CH4 大气负荷，表明我们对这些生态系统贡献的理解存在重大差距CH4 排放。在这里，我们报告了来自亚马逊流域中部 13 个地点的 2,357 棵亚马逊河漫滩树的茎的 CH4 通量。我们发现土壤气体通过湿地树木逃逸是区域 CH4 排放的主要来源。亚马逊树干的甲烷通量比温带潮湿森林和热带泥炭沼泽森林报告的排放量高出 200 倍，代表观察到的最大的非沸腾湿地通量。树木排放的平均稳定碳同位素值 (δ13C) 为 -66.2 ± 6.4/mil，与土壤生物起源一致。我们估计，洪泛区树木每年排放 15.1 ± 1.8 至 21.2 ± 2.5 太克 CH4，此外还有其他来源的区域性每年排放 20.5 ± 5.3 太克。此外，我们根据涵盖 2010 年至 2013 年期间的常规垂直对流层低层 CH4 剖面，提供了亚马逊流域每年 42.7 ± 5.6 太克 CH4 排放量的“自上而下”区域估计。我们发现我们的“自上而下”估计和“自下而上”组合估计之间非常一致，表明适应永久性或季节性淹没的树木产生的大量 CH4 排放可以解释关闭亚马逊 CH4 预算所需的排放源。