Methane dynamics controlled by subsurface metabolic architecture and tidal cycling in a mangrove wetland

Tidal wetlands play a crucial role in global methane cycling. However, the complex interplay between tidal dynamics, microbial communities, and methane emissions in these ecosystems remains poorly understood. This study investigated methane dynamics and its drivers in the Guandu wetland, a subtropical tidally influenced mangrove mudflat in northern Taiwan, focusing on temporal variations in methane emission, methane concentration, methane oxidation rate, dissolved oxygen concentration, and microbial community structure over a period of tidal recession and inundation. We found that the Guandu wetland was readily transformed into anoxic conditions (at greater mm depth) and acted as a net source of methane and CO2, with emissions peaking at 5-9 hours of atmospheric exposure. Elevated methane emissions are intimately linked to highly variable methane and sulfate concentrations in the subsurface during low tide. In contrast, the compound gradient described here was greatly attenuated during high tides. Distinct community compositions were found between surface and subsurface compartments and between surface compartments with initial and extended exposure or subject to high methane incubations. These lines of evidence suggest that vigorous methane and sulfate cycling and enhanced methane emissions jump start with the development of a strong redox gradient derived from subsurface metabolic architecture and are mediated by the complexly structured community compositions as the tidal recession progresses. This data pattern also highlights the dynamic methane emissions regulated by interwoven abiotic and biotic factors in tidally influenced wetlands and imposes a strong need for multifaceted analyses at a high temporal resolution to better project greenhouse gas emissions from such dynamic environments in the context of climatic change schemes.