Vegetation-driven differences in soil CO2 emissions and carbon-sequestering microbiomes of estuarine salt marsh and mangrove wetlands

Estuarine wetlands, particularly salt marshes and mangroves, play a critical role as blue carbon ecosystems, yet their mechanisms of carbon sequestration and emission remain poorly understood. Vegetation type significantly influences soil microbial communities and CO₂ dynamics, but comparative studies across wetland types are limited. This study investigates the Minjiang River Estuary wetland to quantify vegetation-driven differences in soil CO₂ emissions and carbon-sequestering functional microbiomes among Phragmites australis (salt marsh), Cyperus malaccensis (salt marsh), and Kandelia obovata (mangrove) wetlands. We conducted a one-year field monitoring campaign, measuring soil physicochemical properties (temperature, pH, electrical conductivity, water content), CO₂ emissions, and microbial communities (cbbL gene sequencing). Temperature sensitivity (Q₁₀) of CO₂ emissions was calculated, and microbial networks were analyzed using co-occurrence patterns and random forest modeling. Mangrove (K. obovata) soils exhibited higher pH, moisture, and salinity but 71.5 % lower CO₂ emissions than P. australis wetlands (p < 0.05). Microbial drivers differed by vegetation: Sulfuritortus and Alkalispirillum predicted emissions in salt marshes, while Thioalkalivibrio and Thiobacillus dominated in mangroves (p < 0.05). Specifically, the temperature sensitivity of soil respiration (Q₁₀) was significantly higher in mangrove wetlands than in salt marsh wetlands (2.18 vs. 1.28–1.95), indicating greater climate vulnerability. Network analysis revealed mangrove microbiomes were more stable and interconnected, correlating with suppressed emissions. These findings reveal that mangroves demonstrate superior carbon sequestration potential, attributed to distinct microbial consortia and soil properties, thus supporting their prioritization in blue carbon strategies. Crucially, however, their temperature-sensitive CO₂ emissions also highlight a significant vulnerability under warming conditions. This dual insight advances the mechanistic understanding of wetland carbon-climate feedbacks and informs the development of more effective nature-based climate solutions.