Abstract: To understand the responses of belowground biomass of subtropical Chinese fir plantation to global warming, the allocation of root biomass in different soil layers and diameter classes were examined in an experiment with open-top chamber (OTC) to simulate climate warming. Air warming did not affect total root biomass, fine root biomass, and coarse root biomass. Air warming significantly decreased the proportion of fine root in the 20-50 cm soil layer and that of coarse root in the 0-10 cm soil layer, but significantly increased that of coarse root in the 20-50 cm soil layer. Neither fine root biomass nor coarse root biomass in other soil layers was significantly influenced by air warming. Air warming did not affect fine root and coarse root biomass in all diameter classes. Overall, after air warming, Chinese fir saplings could increase the proportion of coarse root biomass in deep soil to support growth, and maintain fine root biomass in topsoil by reducing the proportion of deep fine root biomass to ensure the uptake of nutrients and water. Air warming affects the allocation of root biomass in different soil layers and diameter classes, as well as belowground carbon allocation, with consequences on carbon cycling.

Key words: air warming, root biomass, diameter class, vertical distribution, Cunninghamia lanceolata.