土壤积盐与脱盐过程中N2O排放及其对水盐动态的响应机制

Soil is one of the most important source of atmospheric nitrous oxide (N2O). Change in soil salinity led to change in soil environmental, soil microorganism properties and the transformation of soil nitrogen, that will lead to change in soil N2O emission. Soil salinity might be accumulated during saline irrigation, yet be reduced during soil desalinization by leaching. Meanwhile, soil salinity is closely connected with change in soil moisture, which was a dominate factor that triggering soil N2O emission. Yet, knowledge on soil N2O emission as effected by soil moisture and salinity during different soil salinity change process is far from clear. Take soil under different salt accumulating or desalting processes (realized by different irrigation or drainage management) as example, N2O emission from soil under different salt accumulating or desalting processes were measured for three years consecutively, to reveal the response of N2O emission to soil moisture and salinity dynamics, and difference among different soil salinity change treatments. At the same time, soil environmental and microorganism properties were measured either during field measurement or cultivation experiments, to quantify the impact of soil salinity on different sub segment of nitrogen transformation and N2O production at different soil moisture levels, and hence to reveal the links between ‘soil moisture and salinity dynamics’-’soil environmental factors’- ‘soil microorganism properties’-’N2O emission’. The results will enhancing the understanding on potential change in soil N2O emission from soil irrigated with brackish water (salt accumulation) or saline soil under reclamation (soil desalting), and be helpful to answer if it possible to mitigate the N2O emission (including reduce the increment in N2O emission) by choosing suitable soil water and salinity management practice either during soil salt accumulation or soil desalting.

土壤被认为是温室气体氧化亚氮(N2O)的重要排放源。土壤盐分会影响土壤环境、土壤微生物特性及土壤氮转化，N2O产生与排放也会受到影响，但相关的研究还不充分。在微咸水灌溉与淋洗改良条件下土壤盐分呈截然不同积盐和脱盐趋势，且盐分变化过程与水分这一N2O排放主导因子之间高度相关，目前综合考虑不同盐分变化方向、水盐同步变化对土壤N2O排放影响的研究还有待开展。以不同水管理下土壤积盐和脱盐两个截然不同的盐分变化过程为切入点，通过多年连续监测，明确土壤N2O排放对水盐动态的响应规律及不同盐分变化方向上的差异，进而结合特定的培养试验明确盐分对土壤N2O多个产生环节的定量影响，揭示水盐动态、土壤非生物及生物因子与N2O产生排放之间的内在作用机制。研究可为认识微咸水灌溉和盐渍土改良过程中土壤N2O排放可能产生的变化提供理论依据，并为能否通过合理水盐调控减少这些过程中N2O排放（或减少增加幅度）提供依据。

农田土壤是大气N2O最主要的排放源之一，深入了解不同类型土壤的N2O产生机制和排放动态，对于准确评估N2O排放和制定相应减排策略具有重要意义。然而，目前对于含盐土壤的氮素转化和N2O排放特征仍缺乏了解。本项目通过开展土箱试验、室内土壤培养试验和田间小区试验，结合实时荧光定量PCR法、化学抑制法、同位素标记示踪法等多种试验手段，旨在了解盐分在影响含盐土壤氮素转化和N2O排放特征中的角色。研究结果发现，在不同水分条件下，均存在一定盐度范围，显著促进了土壤的N2O排放；土壤N2O排放及N2O剖面浓度对盐分变化的响应在多种类型土壤上具有一致的规律，且在土壤积盐和脱盐两个相反盐分变化方向上具有一致性；化学抑制法和15N-18O双同位素标记示踪法结果共同证实，一定盐度范围内盐分诱导N2O产生量的增加主要来自硝化细菌反硝化作用和反硝化菌反硝化作用；土壤盐度在一定范围内可同时促进N2O排放和NH3挥发，生物炭施用可减少盐渍土NH3排放量，硝化抑制剂DMPP施用抵消了1.0 dS m-1土壤盐度对土壤N2O排放的促进作用。研究结果可为评价盐渍土农业利用过程中农业措施应用的生态效应和制定减排的水-盐-氮调控策略提供科学依据和思路。