水稻土和菜田添加碳氮后的气态产物排放动态

【目的】动态连续监测添加碳氮底物后各气体产物—O2、 NO、 N2O、 CH4和N2的排放,对土壤碳氮转化过程和气体产生过程做更深入的理解,揭示不同土地利用方式典型红壤的温室气体产生机制。【方法】采集长江中游金井小流域不同土地利用方式稻田和菜地土壤为研究对象,利用全自动连续在线培养检测体系(Robot系统),通过两组试验分别研究土壤碳氮转化过程中各气体产物的动态变化。试验1采用菜地和稻田土壤进行好气培养,设置不施氮对照、 添加40 mg/kg铵态氮、 添加40 mg/kg铵态氮+1%硝化抑制剂、 添加40 mg/kg硝态氮、 添加40 mg/kg硝态氮+1%葡萄糖、 缺氧条件下添加40 mg/kg硝态氮+1%葡萄糖6个处理。试验2采用稻田土壤进行淹水培养,设不施氮对照、 添加40 mg/kg铵态氮、 添加40 mg/kg铵态氮+1%硝化抑制剂、 添加40 mg/kg铵态氮+1%秸秆、 缺氧条件下添加40 mg/kg铵态氮+1%的葡萄糖、 添加40 mg/kg硝态氮、 添加40 mg/kg硝态氮+1%葡萄糖、 缺氧条件下添加40 mg/kg硝态氮+1%葡萄糖8个处理。培养温度均为20℃,土壤水分含量为70% WFPS (土壤孔隙含水量),培养周期为15天。【结果】从菜地和稻田土壤不同碳氮添加处理气态产物及无机氮的动态变化可看出: 1)菜地土壤好气培养初期硝化作用产生了大量N2O; 受低碳和低含水量的限制,反硝化作用较弱。当提供充足碳源和厌氧条件,出现N2O和NO的大量排放。2)在好气稻田和淹水稻田培养过程中,反硝化作用是N2O产生的主要途径。3)稻田土壤中,提供充足碳源和厌氧条件,各气态产物出现的顺序依次是NO、 N2O和N2,与三种气体在反硝化链式反应过程中的生成顺序一致。淹水稻田加铵态氮和碳源处理N2为主要产物,添加硝态氮处理后,N2O成为主要气态产物。当土壤碳源充足时,反硝化过程进行彻底,反硝化产物以终产物(N2)为主。4)在稻田土壤出现厌氧或添加碳源条件下,均检测到大量CH4产生; 且在甲烷产生的同时,NO-3几乎消耗殆尽。【结论】金井小流域典型红壤菜地N2O主要来自于硝化作用,好气和淹水稻田N2O主要来源于反硝化作用; 当碳源充足和厌氧时,菜地及稻田反硝化作用增强; 反硝化产物组成、 产物累积量及出峰顺序与碳源和氧气浓度有关。

Dynamics of gaseous production after addition of carbon and nitrogen in paddy and vegetable soils

Objectives]The continuous monitoring of gaseous emission of carbon and nitrogen products including O2 , NO, N2 O, CH4 and N2 in soils after addition of carbon and nitrogen substrates will help to reveal the mechanism of greenhouse gases generation in typical red soils under different land uses.Methods]Paddy and vegetable soils were collected under different land uses in the Jinjing watershed, middle and lower of Yangtze River.Two experiments were designed at 20℃and 70%WFPS using automatic continuous online incubation and Robot testing system for 15 days.Experiment 1 was designed with six treatments including no nitrogen control, adding 40 mg/kg of ammonium N, 40 mg/kg of ammonium N+1%nitrification inhibitor, 40 mg/kg of nitrate N, 40 mg/kg of nitrate N+1% glucose under aerobic incubation, and 40 mg/kg of nitrate N +1% glucose under anaerobic conditions, using vegetable and paddy soils, respectively.Experiment 2 contained eight treatments: no nitrogen control, adding 40 mg/kg of ammonium N, 40 mg/kg of ammonium N+1% nitrification inhibitor, 40 mg/kg of ammonium N +1% straw, 40 mg/kg of ammonium N +1% glucose under anaerobic conditions, 40 mg/kg of nitrate N, 40 mg/kg of nitrate N+1%glucose, and 40 mg/kg of nitrate N+1%glucose under anaerobic conditions.Results]Nitrification was main pathways of N2 O emissions in the initial stage of aerobic incubation, denitrification was limited because of the low carbon and water content in vegetable soil.However, N2 O and NO emissions were enhanced due to supply of adequate carbon and anaerobic conditions.Denitrification was the main pathway of N2 O production in both aerobic incubation and waterlogged paddy soils.The generation of the gaseous products ranked of NO, N2 O, and N2 when providing adequate carbon and anaerobic conditions in paddy soils, which was consistent with the order of three gases in the reaction chain of denitrification.N2 was the major product in waterlogged paddy soils with the application of ammonium nitrogen and carbon, N2 O became the major product after adding nitrate.The main final product of denitrification was N2 O under adequate soil carbon source condition. Large amounts of CH4 were detected under anaerobic conditions or adding carbon and NO3-was almost depleted when CH4 was generating.Conclusions]N2 O emission was mainly from nitrification in vegetable garden and produced from denitrification in aerobic and flooded paddy field in Jinjing watershed; denitrification of vegetable garden and paddy field was enhanced when enough carbon and anaerobic conditions provided;the composition and rates of denitrification products and the sequence of emission peaks were influenced by carbon and oxygen concentration.