Community structure and ecosystem carbon stock dynamics along a chronosequence of mangrove plantations in China

Mangrove plantations exhibit a high potential for biomass carbon sequestration, however, their effects on soil organic carbon (SOC) accumulation remains unclear. We examined the dynamics of community structure and ecosystem carbon accumulation along a chronosequence of Sonneratia apetala plantations on Qi’ao Island, China. To reveal the self-thinning pattern of S. apetala plantations, 114 quadrats were randomly established in the S. apetala plantations. Four quadrats were selected for soil sampling from differently-aged (4, 9, and 15 years) S. apetala plantations, a 15-year-old S. apetala + Bruguiera gymnorrhiza plantation and a 40-year-old mature Kandelia obovate community. We found that the self-thinning process happened in these S. apetala plantations. The vegetation biomass was found to significantly increase with forest age and the 15-year-old S. apetala and 15-year-old S. apetala + Bruguiera gymnorrhiza plantations had similar total biomass as the 40-year-old K. obovate community. Notably, SOC content and stocks only showed a minor increment along the chronosequence of S. apetala plantations, and SOC stock of the 15-year-old S. apetala community was less than 60% of that of the 40-year-old K. obovate community. The 15-year-old S. apetala + B. gymnorrhiza community had a similar biomass value as the 15-year-old S. apetala community, but the former community had a significant higher SOC stock than the latter. Biomass increment and SOC accumulation are unsynchronized with mangrove plantation development, and monospecific mangrove plantations may not be able to significantly accelerate SOC sequestration in the early plantation stage. Multi-specific plantations may facilitate SOC accumulation more than monospecific plantations.