Soil organic carbon and its water-extractable fraction in volcanic ash soils in a Japanese temperate forest; Relations to phosphate absorption coefficient and their implication

Nagano, Hirohiko   ; Tanaka, Sota; Atarashi-Andoh, Mariko  ; Koarashi, Jun   

Soil organic carbon (SOC) is a key component in global carbon cycling, while water-extractable organic carbon (WEOC) in soils is a proxy of soil carbon available to the living microbial community. Volcanic ash soils, a soil type dominant in Japan, are known to have a very high ability to stabilize soil carbon, and SOC content often correlates with phosphate absorption coefficients (PAC) in soils. In this study, we compared the SOC-PAC relationship and the WEOC-PAC relationships using 42 volcanic ash soils (0-6 cm depth) collected from a Japanese temperate forest. SOC showed a very strong correlation with PAC (r = 0.72). Correlation between SOC and WEOC was also strong (r = 0.84). Correlation between WEOC and PAC was, however, weak (r = 0.42). Thus, water destabilized carbon likely originated from residual carbon sources other than the primary carbon that is highly stabilized in volcanic ash soils.