不同施肥下根际沉积对秸秆碳氮在土壤剖面中固存的影响

Effects of Rhizodeposition on Straw Carbon and Nitrogen Sequestration in Soil Profile Under Different Fertilization Conditions

【目的】秸秆还田是我国东北黑土地保护的重要措施。在实际的农业生产中秸秆与根际沉积同时存在,然而关于它们同时存在时秸秆碳氮在土壤中的固定特征仍不清楚。本研究旨在比较不同土层土壤有机碳(SOC)中秸秆碳(13C-SOC)和土壤全氮(TN)中秸秆氮(15N-TN)含量的差异,探讨不同施肥下根际沉积对秸秆碳氮在土壤中固存的影响,以期为东北黑土地的保护和利用提供依据。【方法】以沈阳农业大学长期定位试验站不同施肥处理(不施肥,CK;单施化肥,NP)为研究对象,分别仅添加13C15N双标记秸秆(S)和添加13C15N双标记秸秆结合根际沉积(以下简称“根际沉积”)(SR),即设CK+S、CK+SR、NP+S和NP+SR 4个处理。分别在田间原位试验的第50天和第150天采样,并测定不同土层SOC含量及其δ13C值、TN含量及其δ15N值。【结果】在秸秆分解前期(第50天),施肥、根际沉积及其交互作用显著影响(P<0.05)表层(0—20 cm)土壤的13C-SOC和15N-TN含量。第50天,CK+SR与CK+S处理相比,表层土壤的13C-SOC和15N-TN含量分别增加了18.6%和21.7%(P<0.05);不同施肥下,S(CK+S和NP+S)与SR(CK+SR和NP+SR)处理表层土壤13C-SOC对SOC的贡献率平均分别为10.5%和12.0%;CK下两个处理(CK+S和CK+SR)与NP下对应的处理(NP+S和NP+SR)相比,表层土壤15N-TN对TN的贡献率平均增加了27.6%(P<0.05)。第50天,深层土壤(20—50 cm)13C-SOC对SOC的贡献率和15N-TN对TN的贡献率分别为1.0%—2.2%和0.5%—0.9%。在秸秆分解后期(第150天),根际沉积和施肥分别显著影响(P<0.05)表层土壤13C-SOC和15N-TN含量。第150天,仅添加秸秆处理与根际沉积处理相比,表层土壤13C-SOC含量增加了12.6%(P<0.05);CK下两个处理与NP下对应的处理相比,表层土壤15N-TN含量平均增加了22.0%(P<0.05);CK各处理和NP各处理表层土壤15N-TN对TN的贡献率平均分别为5.5%和4.0%。第150天,深层土壤13C-SOC对SOC的贡献率和15N-TN对TN的贡献率分别为0.8%—3.2%和0.7%—1.8%。【结论】秸秆分解后期根际沉积对表层土壤中秸秆碳的固定起负反馈效应,秸秆碳氮不断从表层土壤向深层土壤迁移和累积,其对土壤有机碳和氮库稳定性的影响应予以重视。

【Objective】Straw returning is an important measure for protecting black soil in Northeast China.Straw and rhizodeposition coexisted in the practical agricultural production,while the sequestration characteristics of straw carbon(C)and nitrogen(N)in soils remained not very clear under this condition.The purpose of this study was to compare the differences in the content of soil organic C(SOC)derived from straw C(13C-SOC)and that of soil total N(TN)derived from straw N(15N-TN)among different soil layers,and to investigate the effects of rhizodeposition on straw C and N sequestration in soil profile under different fertilization conditions,so as to provide a basis for the protection and utilization of black soil in Northeast China.【Method】Based on the long-term experimental station of Shenyang Agricultural University,the treatments of adding 13C15N double-labeled straw(S)and its combination with rhizodeposition(hereafter referred to as“rhizodeposition”)(SR)were designed under different fertilization plots(no fertilization,CK;single application of chemical fertilizer,NP),including four treatments:CK+S,CK+SR,NP+S,NP+SR.The contents of SOC and TN,and values ofδ13C andδ15N at different soil layers were measured after the 50 and 150 days of in-situ experiment.【Result】At the early stage of straw decomposition(the 50th day),fertilization,rhizodeposition and their interactions significantly affected(P<0.05)the contents of 13C-SOC and 15N-TN in the topsoil(0-20 cm).On the 50th day,compared with the CK+S treatment,the CK+SR treatment increased the contents of 13C-SOC and 15N-TN in the topsoil by 18.6%and 21.7%(P<0.05),respectively.The contribution percentage of 13C-SOC to SOC in the topsoil was,on average,10.5%and 12.0%in the S(CK+S and NP+S)and SR(CK+SR and NP+SR)treatments under different fertilization,respectively.The contribution percentage of 15N-TN to TN in the topsoil was,on average,higher 27.6%(P<0.05)in the two treatments under CK(CK+S and CK+SR)than that in the corresponding treatments under NP(NP+S and NP+SR).On the 50th day,the contribution percentage of 13C-SOC to SOC and that of 15N-TN to TN at deep soil(20-50 cm)were 1.0%-2.2%and 0.5%-0.9%,respectively.At the later stage of straw decomposition(the 150th day),rhizodeposition and fertilization significantly affected(P<0.05)the contents of 13C-SOC and 15N-TN in the topsoil,respectively.On the 150th day,compared with the treatment of rhizodeposition,the treatment of straw addition increased the 13C-SOC content in the topsoil,on average,by 12.6%(P<0.05).The 15N-TN content in the topsoil was,on average,higher 22.0%(P<0.05)in the two treatments under CK than that in the corresponding treatments under NP.The contribution percentage of 15N-TN to TN in the topsoil in CK and NP treatments was 5.5%and 4.0%,respectively.On the 150th day,the contribution percentage of 13C-SOC to SOC and that of 15N-TN to TN at deep soil were 0.8%-3.2%and 0.7%-1.8%,respectively.【Conclusion】Rhizodeposition had a negative feedback effect on the sequestration of straw C in topsoil during the later stage of straw decomposition.Straw derived C and N were constantly migrated and then accumulated from topsoil to deep soil,and their influences on the stabilities of soil organic C and N pools should be paid more attention.