High Methane Production and Emission From Tropical Seagrasses Through Methylotrophic Methanogenesis

Abstract

Methane (CH₄) is a potent greenhouse gas that reduces the carbon sequestration capacity of seagrass meadows. However, our understanding of CH₄ production and emission from these important carbon sinks is limited. Here we conducted biogeochemical experiments to identify methylotrophic methanogenesis as the primary methanogenesis pathway in a tropical seagrass meadow. The production rate constant was 2.2–3.9 d⁻¹, significantly higher than those in temperate meadows (<0.02 d⁻¹). The CH₄ emission rate from the meadow was 835 ± 124 μmol m⁻² d⁻¹. A global meta-analysis further revealed the CH₄ emission rate in tropical seagrass meadows is approximately 8 times higher than temperate meadows. Global seagrass meadows emit 0.3 Tg CH₄ yr⁻¹, with over 90% from tropical meadows and resulting in an 8.6% reduction of the seagrass carbon burial on a 20-year time horizon. These findings highlight the role of tropical seagrass meadows as CH₄ sources, which can offset the benefits of seagrass carbon sequestration.