秸秆还田对南方稻田土壤N_(2)O排放及硝化和反硝化微生物群落的影响

Effects of Straw-returning on N_(2)O Emission and Nitrifying/Denitrifying Microbes in Paddy Soil in Southern China

【目的】以我国南方典型赤红壤水稻土为研究对象,探究不同秸秆还田量对双季稻区晚稻季土壤N_(2)O排放特征及硝化和反硝化微生物的影响,旨在为南方稻田N_(2)O减排提供科学依据。【方法】以2015年设置的定位试验为研究平台,设计5个处理:(1)CK,化肥+无秸秆还田;(2)CKS,化肥+当季秸秆全量还田;(3)S10,化肥+当季秸秆全量还田+秸秆替代10%钾肥;(4)S20,化肥+当季秸秆全量还田+秸秆替代20%钾肥;(5)S30,化肥+当季秸秆全量还田+秸秆替代30%钾肥。采用密闭静态暗箱-气相色谱法及宏基因组测序对气体和土壤微生物进行检测。【结果】稻田土壤N_(2)O排放主要集中在水稻分蘖期;较CK处理,秸秆还田各处理显著降低了稻田土壤N_(2)O累计排放量,其中,S30处理的N_(2)O累计排放量最低,为0.09 kg·hm^(-2),其全球增温潜势也最低;硝化过程中,氨氧化细菌(amoA和amoB)在分蘖期和成熟期的优势菌属均为甲基孢囊菌属;反硝化过程中,nirK型反硝化细菌的芽单胞菌属、罗河杆菌属、丰祐菌属在分蘖期和成熟期细菌属中均占据主导地位;nirS型反硝化细菌的嗜甲基菌属和甲基营养型反硝化菌属在分蘖期和成熟期细菌属中均占据主导地位;分蘖期,土壤N_(2)O排放量与nirS型反硝化细菌的甲基营养型反硝化菌属呈显著负相关、与nirS型反硝化细菌的沙壤土杆菌属呈显著正相关;成熟期,土壤N_(2)O排放量与nirS型反硝化细菌的水生细菌属呈极显著正相关关系。【结论】秸秆还田显著降低了稻田土壤N_(2)O排放,AOB(amoA)和AOB(amoB)的甲基孢囊菌属是氨氧化过程的优势菌属,nirK型反硝化细菌的芽单胞菌属、罗河杆菌属、丰祐菌属,和nirS型反硝化细菌的嗜甲基菌属及甲基营养型反硝化菌属是反硝化过程的优势菌属。

【Objective】Effects of returning spent straws to soil after crop harvest as a conditioner/fertilizer on the N2O emission and nitrifying/denitrifying microbes on a double-cropping rice field in late season were studied.【Method】Based on a positioning experiment set up in 2015,the field soil was treated with(1)chemical fertilizer without straw-returning(CK),(2)chemical fertilizer+100%straw-returning in same season(CKS),(3)CKS+straws to replace 10%potassium fertilizer(S10),(4)CKS+straws to replace 20%potassium fertilizer(S20)or(5)CKS+straws to replace 30%potassium fertilizer(S30).N_(2)O emitted and microorganisms in the soils were detected using the closed static dark box-gas chromatography and metagenomic sequencing technique.【Result】N_(2)O was released from the paddy soils basically during the rice tillering stage.Compared with CK,returning spent straws to the ground significantly reduced the cumulative gas emission from the soil under the S30 treatment,which rendered the lowest rate at 0.09 kg·hm^(-2),and thus,the least contribution to global warming.Of the nitrifying microflora in soil,the dominant genus of ammonia-oxidizing bacteria(i.e.,amoA and amoB)at the tillering and mature stages was Methylospora.Among the denitrifying microbes,the nirK-type Gemmatimonadetes,Rhodobacter,and Opitutus and the nirS-type Methylobacillus and Methylotenera were dominantly present.At the rice tillering stage,the N_(2)O emissions were significantly inversely correlated with Methylotenera but positively with Ramlibacter.At the mature stage,a significant correlation between the soil N2O emission and Aquabacterium population was observed.【Conclusion】By returning the spent straws to the field,a significant reduction on the N_(2)O emissions from paddy soil was resulted.And Methylospora was the dominant genus involved in the ammonia oxidation,whereas the nirK-type Gemmatimonadetes,Rhodobacter and Opitutus and the nirS-type Methylobacillus and Methylotenera were the dominant genera of denitrifying bacteria.