Divergent mineralization of exogenous organic substrates and their priming effects depending on soil types.

The priming effect (PE) induced by exogenous organic substrate input plays an important role in the soil carbon balance. However, little is known about how the chemical complexity of different exogenous organic substrates and soil type regulate the PE. Therefore, we conducted a 72-day incubation experiment involving the addition of three 13C-labelled substrates (glucose, starch and cellulose) to two forest soils with contrasting textures (i.e., a fine-textured clay soil and a coarse-textured sandy soil). Cellulose had a lag phase in the mineralization process but induced greater PE compared to glucose and starch in both soils. Moreover, exogenous organic substrate input generally induced negative PE and net soil C gain in the clay soil, but positive PE and net soil C loss in the sandy soil. The negative PE in the clay soil was negatively correlated with exogenous C mineralization, indicating that preferential substrate utilization was the mechanism controlling PE in the clay soil. However, the positive PE in the sandy soil was positively correlated with exogenous C mineralization, microbial biomass C (MBC), cellulase activity and soil inorganic N content, suggesting that co-metabolism was the mechanism regulating PE in the sandy soil. The significant difference in PE between the clay and sandy soils was mainly attributed to their significant differences in soil MBC, dissolved organic C (DOC) and SOC contents, followed by soil texture (particularly the clay content), available N content and pH. Overall, our results demonstrate that soil type is much more important than substrate type in regulating the PE and that the clay soil has a greater C storage potential than the sandy soil following the input of exogenous organic substrates. [ABSTRACT FROM AUTHOR]