A laboratory incubation experiment was conducted using the 14C isotope labeling technique to study the characteristics of organic carbon mineralization and their response to glucose addition when treated with a combination of straw and chemical fertilizer (ST), inorganic fertilizer (NPK), and non-fertilization (CK). The cumulative mineralization rate (ratio of accumulated mineralization amount to total organic carbon content) in CK reaches 1.64% at the end of incubation (56 days). The cumulative mineralization rate during NPK and ST treatments is significantly lower than that in CK (by 0.34% and 0.39%, respectively). This indicates that long-term fertilization affects the soil carbon sequestration. Varying long-term fertilization influences the response of paddy soil to glucose addition and leads to different levels of the priming effect. The priming effect on soil organic carbon mineralization of the three treatments gradually changes from negative to positive with increasing incubation time. The significantly negative cumulative priming effect in ST and NPK after 56 d is 22.07 and 9.05 times higher than that in CK, respectively. The results of the structural equation model indicate that the NH4+-N and DOC contents indirectly influence the cumulative priming effect on soil organic carbon by affecting the MBC and MBN contents. The NH4+-N concentration has a direct and significant negative effect on the cumulative priming effect. In conclusion, long-term fertilization treatments reduce the cumulative organic carbon mineralization rate of paddy soil. Fertilizer, especially the combination of straw and chemical fertilizer, enhances the soil carbon sequestration and accumulation.
Keywords: isotope labeling technique; long-term fertilization; organic carbon mineralization; paddy soils; priming effect.