Measurements of carbon efflux from exposed and submerged sediment surfaces using the automatic open/close chamber method in a mangrove forest ― A challenge to clarify carbon dynamics in the pedosphere

We measured the CO₂ flux from sediment surfaces (soil respiration in the pedosphere to the atmosphere) in a mangrove forest using an improved automatic open/close chamber (AOCC) method. Soil respiration rates and environmental factors were continuously measured from 4 to 8 July, 2013, in a mangrove dominated by Bruguiera gymnorrhiza. Variation in respiration rate did not exhibit a clear correlation with soil temperature. However, tidal effects were related to variation in soil temperature and may also have contributed to variation in respiration rate. High respiration rates were detected immediately before submergence or after exposure, due to the physical effects of tidal variation. Respiration rates during the period of exposure were lower than those in terrestrial ecosystems, likely due to three factors unique to mangrove forests: soil respiration measurements generally do not include root respiration, organic matter decomposition is restricted to a shallow anaerobic area, and some mineralized carbon is lost as dissolved inorganic carbon. Respiration rates during submergence were half of those measured during exposed conditions, suggesting that previous studies overestimated annual soil respiration. Therefore, measuring soil respiration rates during both exposed and submerged conditions using the AOCC method provides a much more accurate understanding of carbon dynamics in the pedosphere of mangrove forests.