长期不同施肥对稻田土壤有机碳矿化及激发效应的影响

通过室内模拟培养实验,结合14C同位素标记技术,研究了不施肥(CK)、单施化肥(NPK)、秸秆还田+化肥(ST)这3种施肥处理下稻田耕层土壤有机碳矿化特征及其对添加外源葡萄糖的响应特征.结果表明,56 d培养实验结束时,CK处理土壤累积矿化率(土壤原有有机碳累积矿化量/土壤总有机碳含量)达到1. 64%,而NPK和ST处理较CK处理显著降低了0. 34%和0. 39%(P 0. 05),表明长期施肥对土壤碳有一定的固持作用.长期不同施肥处理土壤对添加外源葡萄糖的响应有所不同,表现出了不同程度的激发效应.随着培养时间的推移,3种处理土壤碳矿化的激发效应由负激发效应逐渐转为正激发效应. 56 d时,ST和NPK处理土壤的负累积激发效应比CK分别显著提高了22. 07和9. 05倍(P 0. 05).结构方程模型分析表明,土壤NH+4-N和DOC含量主要通过影响土壤MBC和MBN含量间接影响土壤累积激发效应,且NH+4-N对土壤累积激发效应有直接的显著负影响.综上所述,长期施肥降低了稻田土壤原有有机碳累积矿化率,有利于增强稻田土壤碳的固持和积累,秸秆还田加化肥效果更加明显.

Effects of Varying Long-term Fertilization on Organic Carbon Mineralization and Priming Effect of Paddy Soil

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.