In situ addition of layered double hydroxides promotes sulfate-dependent anaerobic methane oxidation and microbial community shifts in freshwater-influenced mangroves sediments

Abstract

Freshwater-influenced mangrove wetlands are significant sources of methane emissions, potentially offsetting up to 27 % of their carbon storage. The targeted reduction of these emissions offers a critical avenue for enhancing climate resilience. While laboratory studies have shown that elevated sulfate concentrations can suppress methane emissions, the in situ-based effects on methane cycling and associated microbial communities remain poorly understood. To explore this, we introduced magnesium-aluminum layered double hydroxides (Mg-Al-SO₄-LDH), a slow-release sulfate mineral, into freshwater-influenced mangrove sediments in Guangzhou, China, over a 74-day period, resulting in sulfate levels that were 8.9 times higher than those of the control. Isotope tracing, full-length 16S rDNA sequencing, and metagenomic analysis revealed that this sulfate augmentation significantly altered the methane cycling and functional microbial communities. Notably, we observed substantial stimulation of sulfate reduction coupled with anaerobic oxidation of methane (SR-AOM) within Mg-Al-SO₄-LDH-attached microbial communities, characterized by a 6.9-fold increase of anaerobic methane-oxidizing archaea (ANME-1b subtype). Contrary to laboratory observations, the elevated sulfate conditions selectively promoted hydrogenotrophic methanogenesis in situ. These findings establish Mg-Al-SO₄-LDH as a promising approach for enhancing SR-AOM activity while modulating methanogenic pathways, offering novel perspectives for methane management strategies and climate change mitigation within mangrove ecosystems.