Organic carbon stock and composition in 3.5-m core mangrove soils (Trat, Thailand)

Mangroves are increasingly recognized as an important component of regional and global carbon cycles especially for their high carbon storage capacity. Global estimation of mangrove soil organic carbon (SOC) storage requires detailed regional studies, but estimates of SOC data in deep soils are currently missing in many countries. Furthermore, little is explored on the molecular composition of mangrove SOC. Here, we assessed the SOC stock in a Trat mangrove forest (Thailand) by collecting deep soils (3.5 m) and analyzed the SOC composition for better understanding its potential sources and influencing factors. The Trat mangrove forest had four times higher SOC stock than has been considered for Thai mangrove forests, with the per-area SOC stock of nearly 1000 Mg C ha–1 which rivals that of Indo-Pacific mangrove forests. The SOC composition analyzed by C/N ratios and spectroscopic techniques differed by tree species and depth. Compositional data principal component analysis revealed that a biological factor (root abundance) had stronger influences than the soil texture (sand versus clay) on the abundance and composition of mangrove SOC. Although surface soil (~1 m) C density was largely controlled by the recent vegetation, deep soil C density reflected other historical processes. This study contributed to a refined estimate of Thailand mangrove SOC stock and revealed that factors influencing SOC abundance and composition differ by tree species and depth. [Display omitted] •Deep soil C storage and SOC composition in mangrove soils are little studied.•Deep soils (3.5 m) were collected and SOC composition was analyzed (Trat, Thailand).•Trat mangrove has high SOC (962 Mg C ha−1) and ecosystem C (1113 Mg C ha−1) storage.•Root abundance has much stronger influences than soil texture on the mangrove SOC.•Surface SOC was affected by root abundance, but deep SOC was by other processes.