Effect of heat-disturbance on microbial biomass carbon and microbial respiration in Chinese fir (Cunninghamia lanceolata) forest soils

Prescribed fire has now become the usual management practice in the Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) plantation in southern China. Heat generated during fire may affect carbon (C) dynamics in soils. We investigated the microbial biomass C (MBC) and microbial respiration in two Chinese fir forest soils (one is not exposed to fire for the past 88 years, and the other is recently exposed to prescribed fire) after soil heating (100 and 200 °C) under three moisture regimes [25, 50 and 75 % of water holding capacity (WHC)]. For both soils, significant reduction in MBC with increasing heating temperature was found. Soils without exposing to fire previously had significantly greater MBC concentration than the fire-exposed soils when heated at 100 or 200 °C. Lower soil water content resulted in higher MBC concentrations in both soils. In contrast, both soils had the highest soil microbial respiration rate at 50 % WHC. Soils without exposing to fire previously had the greatest microbial respiration rates at 200 °C, while the fire-exposed soils when heated at 100 °C had greatest microbial respiration rates. During 14-days post-heat incubation, soil MBC in both soils was greatest after heating at 200 °C and 25 % WHC. However, soil previously exposed to fire had the lowest CO2 evolution when incubated at 25 % WHC.