Despite carbon sequestration being an important service of mangrove ecosystems, many mangrove reforestation projects have little consideration of the carbon sequestration capacity of species to be planted. Species selection is mostly based on growth rate and convenience in planting. In this study, to compare the quantity and quality of carbon stored in soil, four habitats were selected in Haijiang River Estuary, southern China to assess the contribution by different mangrove species to sediment carbon pool. Two 12-year-old mangrove forests of the exotic Sonneratia apetala and native Kandelia obovata, respectively, and the adjacent sandflat and mudflat as unvegetated referencing sites had been studied. The total sedimentary organic carbon and active sedimentary organic content in sediment suggested that after 12 years of growth, (1) mangrove forests significantly increased the organic carbon content of sediment; (2) total organic carbon in the K. obovata forest was higher than that of the S. apetala forest; but (3) the carbon pool of the K. obovata forest was less stable than that of the S. apetala forest. These results corroborated with other studies that the sediment carbon pool of S. apetala forests reached a stable state after 13 years of growth, while that of K. obovata forests gradually stabilised upon long-term (>13 years) growth. Our study confirms that K. obovata is more conducive to capture carbon in long-term mangrove reforestation projects, demonstrating that the provision of this service may not be directly related to apparently relevant plant traits such as growth rate.
Keywords: Active sedimentary organic carbon; Carbon sequestration; Kandelia obovata; Mangrove reforestation; Sonneratia apetala.
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