Carbon isotopes of water-extractable organic carbon in a depth profile of forest soil imply a dynamic relationship with soil carbon

Nakanishi, Takahiro   ; Atarashi-Andoh, Mariko  ; Koarashi, Jun   ; Kokubu, Yoko   ; Hirai, Keizo*

To elucidate the origin and behavior of the water extractable organic carbon (WEOC), we first determined both the C andC of fractionated WEOC by DAX-8 resin in a cool-temperate beech forest soil. The enrichment of C in WEOC with depth reflected the increasing proportion of the hydrophilic (HPI) fraction to the hydrophobic acid (HPOA) fraction. The changes in C indicated that the major source of WEOC and its fractions was old organic matter in the mineral soil. Our results strengthened previous suggestion that the preferential adsorption of HPOA fraction and the preferential leaching of the indigenous soluble organic carbon in the mineral soils. This dynamic equilibrium between WEOC and the much greater soil organic carbon fraction plays an important role in carbon transport and accumulation throughout the soil profile.