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This study examines CH4 and N2O fluxes during the dry season in two distinct areas of the Pantanal: Barranco Alto Farm (BAF), dominated by grasslands, and Passo da Lontra (PL), a forested region. As climate change increases the occurrence of droughts, understanding greenhouse gas (GHG) fluxes in tropical wetlands during dry periods is crucial. Using static chambers, CH4 and N2O emissions were measured from soils and tree stems in both regions, with additional measurements from grass in BAF. Contrary to expectations, PL—characterized by clayey soils—had sandy mud samples that retained less water, promoting oxic conditions and methane uptake, making it a CH4 sink. Meanwhile, BAF's sandy, well-drained soils exhibited minimal CH4 fluxes, with negligible methane uptake or emissions. N2O fluxes were generally higher in BAF, particularly from tree stems, indicating significant interactions between soil type, moisture, and vegetation. These findings highlight the pivotal roles of soil texture and aeration in GHG emissions, suggesting that well-drained, sandy soils in tropical wetlands may not always enhance methane oxidation. This underscores the importance of continuous GHG monitoring in the Pantanal to refine climate change mitigation strategies. [ABSTRACT FROM AUTHOR]

Inundation-adapted trees were recently established as the dominant egress pathway for soil-produced methane (CH4) in forested wetlands. This raises the possibility that CH4 produced deep within the soil column can vent to the atmosphere via tree roots even when the water table (WT) is below the surface. If correct, this would challenge modelling efforts where inundation often defines the spatial extent of ecosystem CH4 production and emission. Here, we examine CH4 exchange on tree, soil and aquatic surfaces in forest experiencing a dynamic WT at three floodplain locations spanning the Amazon basin at four hydrologically distinct times from April 2017 to January 2018. Tree stem emissions were orders of magnitude larger than from soil or aquatic surface emissions and exhibited a strong relationship to WT depth below the surface (less than 0). We estimate that Amazon riparian floodplain margins with a WT<0 contribute 2.2-3.6 TgCH4 yr-1 to the atmosphere in addition to inundated tree emissions of approximately 12.7-21.1 TgCH4 yr-1. Applying our approach to all tropical wetland broad-leaf trees yields an estimated nonflooded floodplain tree flux of 6.4 TgCH4 yr-1 which, at 17% of the flooded tropical tree flux of approximately 37.1 TgCH4 yr-1, demonstrates the importance of these ecosystems in extending the effective CH4 emitting area beyond flooded lands. [ABSTRACT FROM AUTHOR]