LAUSR

ABSTRACT Plant carbon (plant-C) added to soil can accelerate or inhibit the decomposition of native soil organic matter by inducing positive or negative priming effects. The effect of different types of plant-C on the mineralization of the added carbon and of soil organic carbon (SOC) could contribute to understanding the priming effect. An incubation experiment was carried out at 20°C under dark conditions for 28 days. Soluble-C, lipid-C, and recalcitrant-C derived from 13C-labeled maize straw were added at amounts equivalent to 25%, 50%, and 200% of microbial biomass carbon to two soils containing relatively high (159 g kg−1, H-SOC) and low (13 g kg−1, L-SOC) contents of total SOC. Results showed that mineralization rates varied greatly across soils and plant-C types. Independently of the type of plant-C, less than 30% of the added C was mineralized by the end of the incubation. A greater priming effect was observed in the H-SOC than in the L-SOC soil. Recalcitrant-C caused a greater priming effect than lipid-C and soluble-C in the L-SOC soil. Moreover, the type of priming effect caused by lipid-C and soluble-C in the L-SOC soil changed when the amount of added-C increased from 50% to 200% of microbial biomass carbon. Results indicate that SOC and the type of plant-C are important factors controlling the priming effect. Specially, N and other nutrients released during mineralization of recalcitrant-C stimulated microbial activity, causing a greater priming effect.