Enzyme activity and microbial resource limitation mediated the soil priming effect in response to straw C components in Clay and Loam

Priming effect (PE) of soil organic carbon induced by exogenous carbon (C) plays a crucial role in the turnover and storage of soil carbon pool, and it is strongly regulated by soil microorganism and extracellular enzyme. However, the understanding of the strength and microbial mechanisms of PE in response to exogenous carbon components, and where there is microbial resource limitation remains inadequate. Therefore, the aim of the study is to evaluate the microbial mechanisms of PE in response to exogenous carbon components.

Three carbon components of rice straw (Lip-C, Wat-C and Res-C) and whole straw (Str-C) were added to Clay and Loam in laboratory experiment. During incubation, the CO₂ emission and ¹³C abundance were measured. Soil microbial biomass carbon (MBC), soil extracellular enzyme activity, PE and microbial resource limitation were checked at 37- and 65-day after incubation.

Results showed that Wat-C, Res-C and Str-C addition induced positive PE, and the intensity of PE was in the order of Wat-C > Str-C > Res-C. Lip-C addition induced negative PE. The intensity of positive PE in Clay was higher than that of the negative PE in Loam. There were significant relationships between PE and extracellular C, N and P-cycling enzymes, which were much stronger on 37-day than 65-day after incubation. Soil microorganisms in Clay and Loam were largely limited by P and N on 37-day after incubation, respectively. On 65-day, the major microbial resource limitation was P in two soil types, except of N limitation in Clay with Res-C addition. The interaction of microbial growth, enzyme activity and PE depended on straw C component and soil nutrient.

All these findings improved out the knowledge of microbial resource limitation over straw C addition according to soil enzyme activity, and P might be another important driver as well as the effects of C and N on PE. The present results would have potential for predicting soil C dynamic and developing sustainable agricultural practices in the future.