Seasonal and snowmelt-driven changes in the water-extractable organic carbon dynamics in a cool-temperate Japanese forest soil, estimated using the bomb-C tracer

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

Although considerable research has been conducted on the importance of recent litter versus older soil organic matter as DOC sources in forest soil, a more thorough evaluation of the temporal patterns of DOC and WEOC is necessary. We investigated the seasonal variation in water-extractable organic carbon in a Japanese cool-temperate beech forest soil by using the carbon isotopic composition (C and C) of WEOC as a tracer for the carbon sources. Fresh leaf litter DOC significantly contributed to WEOC in May when the snowmelt occurred. In the rainy season, increases in the concentration of WEOC and the proportion of hydrophobic compounds were caused by high microbial activity under wetter conditions. From summer to autumn, the WEOC in the mineral horizons was also dominated by microbial release from the soil organic matter. These results indicate that the origin and dynamics of WEOC are strongly controlled by seasonal changes in the environmental conditions.