土壤羟胺氧化释放N2O的氨氧化微生物与铁锰氧化物耦合作用机制

Hydroxylamine could oxide to emit N2O, which will inevitably affect the entire circulation of nitrogen and greenhouse gas emission in soil, and the oxidation occurs under the combined action of ammonia-oxidizing microorganisms and iron-manganese oxides (Fe-Mn oxides). In this project, the soils enriched Fe-Mn oxides in China (Laterite, Latosolic red soil, Red soil, Yellow soil, Yellow-brown soil, Alluvial soil and Paddy soil, etc) will be studied through isotopic (18O-H2O) tracer technique to find out the contribution of soil hydroxylamine oxidation to N2O emission; meanwhile, real-time fluorescent quantitative PCR will be used to analyze the quantity and activity of ammonia-oxidizing microorganisms gene AOA and AOB amoA, the correlation between the N2O emission quantity in hydroxylamine oxidation, and the dynamic accumulation of hydroxylamine in soil, the form and content of Fe-Mn oxide, ammonia-oxidizing microorganisms gene amoA will be analyze, and illuminate the effects of ammonia oxidation microorganisms coupling with iron-manganese oxide on N2O emission. In addition, a series of iron/manganese oxides with different forms and oxidizability, will be synthetized, microcosmic culture tests will be done to study the effect of iron/manganese oxides coupling with AOA/AOB on N2O emission in hydroxylamine oxidation, to further study the mechanism of different iron/manganese oxides coupling with ammonia-oxidizing microorganisms in driving hydroxylamine oxidation, so as to provide scientific basis for reasonably controlling soil N2O emission.

羟胺氧化释放N2O影响整个土壤氮循环乃至全球温室气体的调控，而该过程在氨氧化微生物和铁锰氧化物耦合作用下完成，明确其生物化学耦合作用机制具有重要的科学意义。本项目拟以我国富含铁锰氧化物的土壤（砖红壤、赤红壤、红壤、黄壤、黄棕壤、潮土、水稻土等）为研究对象，利用同位素18O-H2O示踪技术研究土壤羟胺氧化释放N2O的贡献，采用实时荧光定量PCR技术分析氨氧化微生物AOA和AOB amoA基因的数量与活性，分析羟胺氧化N2O释放量与土壤羟胺的动态积累量、铁锰氧化物形态和含量以及氨氧化微生物amoA基因的相关性，阐明氨氧化微生物和铁锰氧化物对羟胺氧化释放N2O的耦合效应。另外，合成系列不同形态和氧化度的铁锰氧化物，采用微宇宙培养试验研究铁锰氧化物与AOA或AOB耦合作用对羟胺氧化释放N2O的影响，深入研究不同铁锰氧化物与氨氧化微生物耦合驱动羟胺氧化的机制，为合理调控土壤N2O释放提供科学依据。

铁锰氧化物作为土壤中最为活跃的因子之一，其氧化还原过程与土壤N素的生物-非生物转化过程耦合发生，进而影响土壤N2O的排放。本项目系统研究了铁锰氧化物对水稻土硝化过程N2O释放的影响及机制，对全面理解农田土壤氮素循环过程具有重要意义，可为农田土壤N2O合理减排提供科学参考。主要研究结果如下：.1）水稻土N2O释放量受土壤含水量、施肥、土壤性质（pH值、有机质、铁氧化物）等因素影响。水分不饱和时，硝化作用是水稻土释放N2O的重要途径，自养硝化对土壤N2O排放的贡献大于异养硝化，施氮提高土壤自养硝化对土壤N2O排放的贡献。潜育型水稻土N2O释放量显著高于潴育型水稻土，且N2O累积释放量均与土壤铁含量显著相关（p˂0.05）。.2）针铁矿通过生物、非生物耦合效应促进水稻土硝化过程N2O的释放。在60% WHC条件下，水稻土N2O来源以生物过程为主，非生物过程贡献较低。供试水稻土氨氧化细菌（AOB）对N2O排放的贡献均高于氨氧化古菌（AOA），针铁矿增加了AOB对N2O排放的贡献，进而促进水稻土N2O的释放。供试水稻土NH2OH非生物过程对N2O释放的相对贡献高于NO2--N，针铁矿减少了NH2OH和NO2--N非生物过程对N2O释放的贡献。.3）土壤水分状况、水钠锰矿含量、土壤类型等因素影响水稻土N2O排放量对水钠锰矿的响应。在恒定含水量条件下，水钠锰矿（0.1%，w/w）显著促进了黄棕壤性水稻土N2O排放；但在周期性水分变化条件下，水钠锰矿对N2O排放起抑制效应。水钠锰矿含量越高，其对土壤N2O释放量的抑制效应越强。水钠锰矿主要通过抑制土壤硝化作用而降低N2O排放，但水钠锰矿对土壤硝化微生物的抑制作用随时间延长逐渐减弱，微生物活性得到一定恢复。.4）碳铁耦合作用显著抑制水稻土N2O的排放，高可溶性有机碳可增加土壤氮素的固持，Fe2+含量的增加及水铁矿促进nosZ反硝化功能基因丰度，促进完全反硝化作用，有利于N2O向N2转化，减少N2O的排放。