土壤中羟胺和亚硝态氮非生物过程对N2O排放的贡献

Contributions of Abiotic Processes Driven by Hydroxylamine and Nitrite to N2O Emission in Six Different Types of Soils in China

摘要:

羟胺（NH₂OH）和亚硝态氮（NO₂⁻-N）均可以通过非生物过程产生N₂O，但是同一土壤中其对N₂O排放的相对贡献尚不明确。本文采用高压灭菌和室内培养方法，测定了采自6个不同地点的农业利用土壤在灭菌和非灭菌条件下添加NH₂OH或NO₂⁻-N后N₂O的排放量，以研究土壤中NH₂OH和NO₂⁻-N非生物过程对N₂O排放的相对贡献及其关键因子。结果表明，供试土壤中，NH₂OH非生物过程产生的N₂O贡献介于6%~73%， NO₂⁻-N非生物过程产生N₂O占的比例为3%~236%；在pH<7的衢州茶园、鹰潭旱地、常熟菜地和海伦旱地土壤中，添加NO₂⁻-N后非生物过程产生N₂O比例大于添加NH₂OH的处理，但是在pH>7的常熟果园和封丘旱地土壤中则相反；pH是影响NH₂OH和NO₂⁻-N非生物过程产生N₂O的关键因子，添加NH₂OH处理中非生物过程产生N₂O占N₂O总排放量的比例与土壤pH呈正相关（p< 0.05），而在添加NO₂⁻-N处理中呈负相关（p< 0.01）。上述结果说明，NO₂⁻-N在偏酸性土壤中可能主要通过非生物过程产生N₂O，而在偏碱性土壤中主要通过生物过程；NH₂OH则与之相反。

Abstract:

【Objective】Nitrous oxide (N₂O) is an important greenhouse gas contributing to global warming and depleting stratospheric ozone. Agricultural soils are the major sources of anthropogenic N₂O emissions. N₂O emitted from natural and cultivated soils is mainly generated through nitrification and denitrification, accounting for about 70% of the global total, but contributions of other processes (such as chemodenitrification) are poorly understood. Hydroxylamine (NH₂OH) and nitrite (NO₂⁻-N) are two main intermediate products of nitrification, and the latter is also an intermediate product of denitrification, both of which can produce N₂O through abiotic processes. However, relative contributions of these two products to N₂O emission in the same soil remain unclear. 【Method】To determine contributions of the two products, NH₂OH and NO₂⁻-N, through abiotic processes in soil to emission of N₂O and to identify related affecting factors, an indoor incubation experiment was designed and carried out, using soil samples collected from a tea garden in Quzhou, an upland field in Yingtan, a vegetable garden in Changshu, an upland field in Hailun, an orchard in Changshu and an upland field in Fengqiu, representing four types of land use. The soil samples, sterilized (autoclaved three times at 121℃ for 1 h before nitrogen fertilization) and unsterilized, were spiked with NH₂OH or NO₂^--N, separately, and incubated. Emissions of N₂O from the soil samples were monitored after 2 hours of incubation. 【Result】Addition of NH₂OH or NO₂^--N increased N₂O emission from each tested soil, with N₂O flux peaking 2 h after the addition of NH₂OH during the observed period, and the highest peak was observed from the soil samples collected from the orchard in Changshu Orchard (1 585 μg kg⁻¹ h⁻¹). N₂O emissions from the soils spiked with NO₂⁻-N varied in the range of 6.42~61.28 μg kg⁻¹ h⁻¹ in flux. In unsterilized or natural soil samples spiked with NH₂OH, N₂O emission coefficients varied from 18.63% to 35.95%, which were 10.03 times~76.46 times that in the soil samples spiked with NO₂^--N. Effect of sterilization on N₂O emission differed between the soil samples spiked with NH₂OH and their respective ones spiked with N₂O⁻-N. Sterilization significantly reduced N₂O emission in all the soil samples spiked with NH2OH, especially in the soil samples from the tea garden in Quzhou, with the reduction reaching, up to 94%, while in the soil samples spiked with NO₂⁻-N, the effect of sterilization was observed only in those from Changshu and Fengqiu, but reverse effects were found in those from Quzhou, Yingtan, Changshu and Hailun. In all the soil samples, abiotic processes of NH₂OH contributed 6%~73% to total of N₂O emission, whereas abiotic process of NO₂⁻-N did 3%~236%. In the soil samples from Quzhou, Yingtan, Changshu and Hailun, all being higher than 7 in pH, abiotic process of NO₂⁻-Ncontributed more than abiotic process of NH₂OH did to N₂O emission but in the soil samples from Changshu and Fengqiu, both being higher than 7 in pH too, reverse trends were found, indicating soil pH is a key factor affecting abiotic N₂O production from NH₂OH or NO₂⁻-N. In the soil samples spiked with NH2OH, the contribution of abiotic process, in terms of proportion, to the total N₂O emission was significantly and positively related to soil pH (p< 0.05), while in the soil samples spiked with NO₂⁻-N, it was negatively related (p< 0.01). 【Conclusion】All the above-describedfindings suggest that the formation of N₂O from NO₂⁻-N is probably mainly attributed to abiotic processes in acid soils and to biotic processes in alkaline soils, while the formation of N₂O from NH₂OH goes just the opposite.