长期秸秆黑炭施用对稻田土壤剖面脱氮过程的影响机制研究

Most concern has hitherto focused on application of biochar to cropland as an option of carbon sequestration and soil reclaimation with virtually little attention paid to the transformation processes of nitrogen (N) when associated with biochar-treated soils. Denitrification and anaerobic ammonium oxidation are the two important processes of N removal pathway from paddy ecosystems, which are closely related to N use efficiency and N losses. Currently, the understanding on the effects of biochar application into paddy fields on denitrification and anaerobic ammonium are lacking. Our results from an incubation study showed that biochar amendment could enhance the rate of N2 production, indicating that biochar may accelerate N removal from paddy fields, resulting more N losses. Aiming to address this phenomenon, in the present project we will select a long-term biochar amended paddy soil with varying biochar application rates for more than 5 years for test. The Membrane inlet mass spectrometer (MIMS) method in combination with 15N tracer technique and varying incubation systems will be used to study on denitrification and anaerobic ammonium oxidation in this paddy soils with long-term biochar amendments. We will investigate the occurrence rates, contribution percentages to N removal, and key influencing factors of these two processes. Finally, the underlying mechanisms of denitrification and anaerobic ammonium responses to biochar amendment will be clarified. The information from this study will provide more sights for biochar-mediated changes in N cycling of paddy ecosystems.

国际上对生物黑炭的关注多聚焦于其固碳减排和改良土壤的功能，而较少关注其施入土壤后对氮素转化过程的影响机制。反硝化和厌氧氨氧化是稻田脱氮过程的两个重要途径，其发生强度直接影响着氮肥利用效率与损失。当前有关黑炭施加对稻田反硝化和厌氧氨氧化影响研究未见报道。申请人前期研究初步结果显示，黑炭施用可提高稻田脱氮过程产物N2产生速率，暗示黑炭可能促进了稻田的脱氮过程。因此，本项目拟利用以往建立的稻田长期秸秆炭化还田试验，采用膜进样质谱（MIMS）直接定量脱氮产物N2方法，结合15N同位素技术和多种培养体系，深入研究长期秸秆炭化还田下稻田剖面土壤反硝化和厌氧氨氧化脱氮过程的发生规律、主控因子及其影响机制，以期为全面科学评价秸秆炭化还田对稻田氮素循环的影响提供必要理论支撑。

越来越多的研究表明秸秆生物质炭可以影响稻田的氮素损失，但对生物质炭施加后深层土壤剖面氮转化过程的影响机制以及稻田脱氮规律的研究较少。因此，本研究通过采集土壤剖面和渗漏水、田面水，利用气相色谱法、15N同位素标记法、氦密闭培养法、近似原位培养法结合膜进样质谱仪，以长期秸秆生物质炭不同施用量下的稻田土壤/水为研究对象，探讨了长期秸秆生物质炭施用对稻田土壤剖面过程的影响规律及机制，取得了以下主要结果：（1）通过测定稻田不同土壤剖面渗漏水溶解性N2O和N2,发现生物炭的施加能降低土壤剖面N2O和N2浓度，秸秆生物质炭还田主要通过增加溶解氧，提高氧化还原电位，进而有效减少深层反硝化及其主要气态产物N2随水流失的风险。（2）发现稻田土壤剖面主要以反硝化作用为主，随土壤深度的增加脱氮发生强度逐渐降低，长期秸秆炭化还田可明显降低土壤剖面的反硝化和厌氧氨氧化发生强度。（3）通过田间监测和近似原位培养初步发现生物炭施加增加田面水中溶解性N2O溶度，但降低了水稻生长季总脱氮损失。相关研究为全面科学评价秸秆炭化还田对稻田氮循环的影响提供了部分理论支撑。截止目前，已发表SCI论文5篇，中文核心论文1篇，授权专利1项。未来，将进一步整理分析数据，深入揭示秸秆炭化长期还田稻田土壤脱氮过程的微生物机制。