Radiocarbon-based residence time estimates of soil organic carbon in a temperate forest: Case study for the density fractionation for Japanese volcanic ash soil

Abstract

The world’s soils store significantly more carbon than that is present in the atmosphere. To understand the distribution and dynamics of the soil organic carbon (SOC) reservoir and make a prediction about the response of the soil carbon pool to climate change, it is necessary to quantitatively constrain rate of soil carbon cycling. Following previous studies [24], we investigated the method for physically preparation of Japanese volcanic ash soil for the mean residence time (MRT) estimates in a cool-temperate deciduous forest in Japan, at one of Asia Flux monitoring sites. Sequentially isolated density fractions clearly differed in C contents and C/N ratios in soil surface (3–8 cm) and deep soil layer (38–43 cm). In soil surface layer, the light fractions (1.6–1.8, 1.6–1.8, 1.8–2.1 g cm−3) accounted for nearly 90% of SOC and their MRT ranged from 6 to 150 year. In deep layer, the 2.1–2.4 g cm−3 fraction accounted for more than 60% of SOC and its MRT was 3100 year. The lighter fractions (1.6–1.8, 1.8–2.1) comprised small portion of total SOC and were significantly slowly MRT (2038–2335 year), although it seems to consist of labile carbon.