Carbon stocks and fluxes of Mangrove Associates(Hibiscus hamabo and Paliurus ramosissimus) in Jeju Island, South Korea

Mangrove associates, generally distributed in the landward fringe of mangrove forests, are one of the major carbon sinks. Mangrove associates are expected to increase in South Korea as their spatial distribution is shifting to poleward with global warming. However, understanding of carbon stocks and fluxes of mangrove associates is still limited. In this study, we estimated carbon stocks in soils and forest floors and measured carbon fluxes of soil CO₂ efflux and net photosynthesis of Hibiscus hamabo and Paliurus ramosissimus, mangrove associates which inhabit naturally in Jeju Island, South Korea from April to October, 2022. Four sites of H. hamabo (Gimnyeong – coast, Hado, Seongsan and Wimi) and P. ramosissimus (Gimnyeong – wetland and Daejeong 1 ~ 3) were selected. Soil carbon stocks at 0 – 10 cm depth from Gimnyeong – wetland, Seongsan, and Hado where soil horizons developed, and forest floor carbon stocks were quantified. In addition, soil CO₂ efflux and net photosynthesis were measured once a month. Mean soil carbon stocks (t C ha^-1) ranged from 29.0 to 30.1 while mean forest floor carbon stocks (t C ha^-1) ranged from 2.8 to 5.8. Soil CO₂ efflux rate (µmol CO₂ m⁻² s⁻¹) in August was significantly higher than that in April and October. There was a positive correlation between soil CO₂ efflux and soil (p < 0.001, r = 0.41) and air (p < 0.001, r = 0.52) temperatures compared to other factors such as soil water content (p > 0.05), and electrical conductivity (p > 0.05). Net photosynthesis (µmol m⁻² s⁻¹) was significantly high in July, and there were no significant differences among sites. Soil carbon stocks of the two species were higher than those of Quercus mongolica forests (27.8) in South Korea. Moreover, forest floor carbon stocks were higher compared to those of Q. glauca forests (1.32) in Jeju Island. Mean net photosynthesis (mean ± standard error, µmol m⁻² s⁻¹) of H. hamabo (8.9 ± 0.9) and P. ramosissimus (8.8 ± 1.3) in July were higher than that of Eleutherococcus gracilistylus (6.74 ± 0.26), a deciduous shrub inhabiting in Jeju Island. This study provides the first data base to estimate carbon stocks and fluxes of mangrove associates in South Korea and the results showed that H. hamabo and P. ramosissimus seem to be promising species for carbon sinks.

Acknowledgement

This study was carried out with the support of the National Research Foundation, Republic of Korea (Project No. 2022R1A2C1011309), and the Warm-temperate and Subtropical Forest Research Center (Project No. FE100-2022-04-2022).