Non-flooded riparian Amazon trees are a regionally significant methane source

Area of Science:

• Environmental Science
• Biogeochemistry
• Ecology

Background:

• Forested wetlands are significant sources of soil-produced methane (CH4).
• Inundation-adapted trees are recognized as a major pathway for CH4 release.
• The role of trees in CH4 emission when water tables are below the surface is not well understood.

Purpose of the Study:

• To investigate CH4 exchange dynamics in Amazonian floodplain forests with fluctuating water tables.
• To quantify CH4 emissions from trees, soil, and aquatic surfaces under varying hydrological conditions.
• To assess the contribution of non-flooded tree pathways to overall methane emissions.

Main Methods:

• Field measurements of CH4 exchange across tree stems, soil, and aquatic surfaces.
• Monitoring of dynamic water table levels at three Amazonian floodplain locations.
• Data collection over four distinct hydrological periods from April 2017 to January 2018.

Main Results:

• Tree stem CH4 emissions were significantly higher than soil or aquatic emissions.
• Tree emissions showed a strong correlation with water table depth below the surface.
• Non-flooded Amazonian riparian margins contribute an estimated 2.2–3.6 Tg CH4 yr-1.

Conclusions:

• Trees act as crucial methane conduits, releasing significant amounts of CH4 even from non-flooded soils.
• This highlights the importance of considering tree-mediated CH4 transport in climate models.
• Tropical wetland trees extend the methane-emitting area beyond flooded zones, impacting global methane budgets.