Abstract: Primary forests play an important role in the global carbon budget. Fine roots in the forests are an integral component of ecosystem carbon cycling. The seasonal dynamics of fine root (≤2 mm) biomass were investigated by sequential soil coring method from May to November in 0-30 cm soil layer ofAbies faxoniana primary forest in sub-alpine region of western Sichuan. Furthermore, fine root productivity and turnover rate were estimated by decision matrix method. The results showed that living fine root biomass and annual production in 0-30 cm soil layer ofA. faxoniana primary forest were 286.89 g·m^-2 and 168.94 g·m^-2·a^-1, respectively. The average fine root turnover rate was 0.56 a^-1. Fine root biomass, productivity and mortality had substantial seasonal variation during the growing season. Living fine root biomass and productivity showed an overall unimodal seasonal trend, peaking in September. Fine root necromass and the ratio of necromass to living biomass of fine root showed a “U” trend, while mortality exhibited an upward trend during the growing season. Soil depth was a significant factor affecting fine root dynamics. Living fine root biomass, fine root necromass, productivity and turnover rate decreased, whereas the ratio of necromass to living fine root biomass slightly increased along soil depth.

Key words: soil microbial biomass P, yellow paddy soil, soil microbial biomass C, long-term fertilization, coupling of C and P