Abstract: Exogenous carbon input may either increase or decrease soil organic carbon (SOC) mineralization, resulting in a positive or negative priming effect, respectively, with consequence on soil carbon storage and stability. However, how differences in exogenous carbon input levels and soil properties affect the direction and intensity of the priming effect remains unknown. In this study, we collected soil samples from two coastal wetlands (new and old river channels) in the Yellow River Delta with different soil physicochemical properties, and conducted an incubation experiment to test the effects of different levels of isotope-labeled glucose addition (0.2%, 0.5% and 2% of SOC) on the priming effect of soil carbon mineralization. The results showed that the 0.2% and 0.5% treatments led to a positive priming effect, whereas the 2% treatment significantly inhibited native SOC mineralization and produced a negative priming effect. There was a significant interaction between wetland type and glucose addition level on the priming effect. There was no significant difference in the priming effect of the two wetlands under the 0.2% and 0.5% treatments. Soil from the old channel wetland produced a stronger negative priming effect than that in the new channel wetland under the 2% treatment. The priming effect was negatively correlated with microbial biomass carbon, suggesting that the differences in soil physicochemical properties, including soil texture, nutrient and organic carbon content, affected soil microbial biomass and activity, thus regulating the response of priming effect to exogenous carbon inputs. Overall, our results suggest that exogenous carbon addition levels and soil physicochemical properties co-regulate the direction and intensity of the priming effect in the coastal wetlands, with important consequence on soil carbon cycle of coastal wetlands. This study provides a scientific basis for understanding soil carbon stability in coastal wetlands.

Key words: soil organic carbon, priming effect, glucose addition, carbon isotope, coastal wetland