Pneumatophore CO₂ effluxes decrease with increased salinity in mangrove forests of Yucatan, Mexico

Although mangrove forests are great carbon sinks, they also release carbon dioxide (CO₂) from soil, plants, and water through respiration. Many studies have focused on CO₂ effluxes only from soils, but the role of biogenic structures such as pneumatophore roots has been poorly studied. Hence, CO₂ effluxes from pneumatophores were quantified at sediment-air (non-flooded sediment) and water-air (flooded sediment) interfaces along a salinity gradient in three mangrove types (fringe, scrub, and basin) dominated by Avicennia germinans during the dry and rainy seasons in Yucatan, Mexico. Pneumatophore abundance explained up to 91% of CO₂ effluxes for scrub, 87% for fringe, and 83% for basin mangrove forests at the water-air interface. Overall, CO₂ effluxes were inversely correlated with temperature and salinity. The highest CO₂ effluxes were in the fringe and the lowest were in the scrub mangrove forests. Flooding decreased CO₂ effluxes from the dry to the rainy season in all mangrove forests. These results highlight the contribution of pneumatophores to mangrove respiration, and the need to include them in our current carbon budgets and models, but considering different exchange interfaces, seasons, and mangrove ecotypes.