冻融作用下无机氮素在农田黑土中的微生物转化过程研究

Freeze-thaw cycles can have strong effects on nitrogen (N) transformation in soils mainly through influencing microbial activity and its population. The freezing-thawing process is critical events in the preceding late autumn and early spring in agroecosystem of northeastern China, while knowledge of its effects on characteristics of soil inorganic N transformation and the underlying mechanisms driven by soil microorganisms is scare. To address this issue, we carried out an incubation study under controlled condition with black soil (Mollisol) amended with 15N-labeled ammonium sulphate ((NH4)2SO4). The aims of our investigation were to identify the transformation rates and amounts of 15N-(NH4)2SO4 into individual amino sugar and amino acid compounds under different frequency and intensity of freeze-thaw cycles, to clarify the relative contribution of fungi and bacteria in the transformation process, and also to address the distribution and stabilization of newly-formed organic N compounds in soil by tracing their quantity in different soil aggregate pools. The newly formed metabolized amino compounds derived from added inorganic N were differentiated and quantified by using an isotope-based gas/liquid chromatography-mass spectrometry technique (GC/MS and LC/MS). It was expected that the microbial mechanism moderating soil N transformation could be clarified in related to freezing-thawing events, and the information of this kind may help to a better understanding of N biogeochemical cycling in Mollisols.

冻融作用通过改变土壤结构和水热状况影响微生物活性，进而对氮素生物地球化学循环过程产生重要影响。从土壤氮素高效管理角度出发，开展冻融作用下氮素的微生物转化过程研究对加深认识土壤氮素循环转化过程及内在的生物驱动机制具有重要意义。东北黑土区在秋末春初季节土壤冻融作用强烈，然而对冻融作用下土壤氮素转化的微生物作用过程仍缺乏深入认识，这限制了对该区氮素循环和调控研究进行科学评价。本研究以东北黑土为对象，采用室内模拟方法，应用稳定同位素示踪技术，以标记肥料氮素向微生物体"关键有机氮组分（氨基酸和氨基糖）"的转化过程为切入点，系统研究不同冻融交替频率和强度下氮素向氨基酸（糖）的转化速率和容量特性，解析冻融作用下微生物对土壤氮素转化和截获的贡献，进一步结合有机氮组分在团聚体中的分布，阐明冻融作用下土壤氮素转化的微生物学作用过程。本研究可丰富黑土区氮素循环转化过程的理论内涵，并为指导氮肥高效利用提供科学参考

冻融交替作用通过改变土壤水热和结构影响土壤微生物活性，进而影响微生物参与的氮素循环过程。在冻融作用强烈的东北黑土区开展氮素的微生物转化过程研究，对土壤氮素高效利用具有重要意义。本项目以东北农田黑土为研究对象，采用稳定同位素示踪技术，研究标记肥料氮素进入土壤有机氮组分（氨基糖和氨基酸）的转化速率和容量特性，进而阐明冻融作用下土壤氮素的转化特征以及微生物的作用过程。结果发现，冻融作用显著影响无机氮素转化过程，而这种影响依赖于底物添加类型和土壤有机质含量。随着培养时间的进行，不同土壤氨基糖的APE值呈现增加的趋势，说明标记氮素逐渐向土壤中积累，但是这种积累的出现早晚与冻融温度有较大的关系。冻融温度较低时，对照土壤中新合成的氨基酸含量显著下降，而有机肥处理土壤中新合成的氨基酸含量增加，说明土壤微生物利用无机氮合成新的有机氮组分，从而减少了土壤氮素损失。本研究暗示在冻融交替发生时，土壤中原有的氮素因土壤结构破坏而暴露出来被微生物利用，从而新合成有机氮组分留在土壤中，这种留存的时间长短与土壤有机质含量密切相关，有机肥处理土壤能够将土壤无机氮素以氨基糖和氨基酸的形式储存起来，更有利于低温条件下土壤氮素的截获。本研究在理论上加深了冻融作用下土壤氮素的转化过程和内在机理的认识，实践上为东北黑土区氮肥合理施用与高效管理提供了理论参考。