Stronger ecosystem carbon sequestration potential of mangrove wetlands with respect to terrestrial forests in subtropical China

Mangrove wetlands and terrestrial forests are considered as important carbon sinks for alleviating climate changes, but the sequestration processes and regulations of climate factors on controlling the variability of carbon fluxes of these ecosystems may differ. In order to compare the different mechanisms of carbon sequestration in mangrove and terrestrial forest ecosystems, we analyzed ecosystem CO2 flux data measured by eddy covariance (EC) technique from four forests ecosystems in subtropical China: two mangrove wetlands and two terrestrial forests. Our results showed that the mangrove wetlands could sequester much more carbon than the nearby terrestrial forests because of significantly higher gross ecosystem production (GEP) and lower ecosystem respiration (Re) values. Moreover, our analysis of the responses of net ecosystem exchange (NEE) to photosynthetically active radiation showed that the mangrove wetlands had lower light compensation point but higher maximum photosynthesis rates than the terrestrial forests. Furthermore, the relationships between Re and air temperature (Tair) showed the ecosystem respiration rate (Reref) at 20 °C values were lower but that the temperature sensitivity (Q10) values were higher in the mangrove wetlands than in the terrestrial forests, which might be caused by tides in the mangrove ecosystems. In addition, the relationships between the logarithmic values of soil organic carbon ln(SOC) and δ13C indicated that SOC decomposition rates were lower in mangrove forests than in terrestrial forests, which thus led to lower Re values compared to terrestrial forests. Our results imply that mangrove forests can sequester more CO2 from the atmosphere than nearby terrestrial forests due to relatively higher GEP and lower Re values. Moreover, the regulation of ecosystem carbon exchange by tides in mangrove wetlands should be investigated in more detail in future studies.