Abstract
Apart from the well-known ecosystem services of mangroves in the coastal regions, mangroves recently have been recognized as a major repository of carbon. However, little is known about the carbon storage in the mangroves as soil aggregates and, we envisage that studying soil aggregates under mangroves in comparison with upland forest soil aggregates would yield valuable information about the process of carbon storage. Therefore, this study aims to elucidate comparatively, the characteristics of soil aggregates of mangrove and upland forest soil, separated by density fractionation. Samples were collected from a mangrove ecosystem and an upland forest area in the northern region of Okinawa Island. Four density fractions (<1.6, 1.6～2.0, 2.0～2.5 and >2.5 g cm-3 fractions) were separated by sodium polytungstate with three density levels (1.6, 2.0 and 2.5 g cm-3). Carbon and nitrogen content and C/N ratio were highest in the lighter fractions and decreased with increasing density. Clay and silt minerals and sand and silt minerals were included in the low-density fractions (<1.6, 1.6～2.0 g cm-3) and high-density fractions (2.0～2.5 and >2.5 g cm-3) respectively. In the upland forest soil, highest clay and carbon percentages were observed in the 1.6～2.0 g cm-3 fraction. However, mangrove soil had the highest carbon content in the 1. 6～2.0 g cm-3 fraction, which, on the contrary, had low clay content. Therefore, it can be suggested that clay minerals are necessary to stock carbon in the upland soil. However, it was not the case for the mangrove soil.
https://ror.org/03ss88z23 
