土壤温度、水分和NH_4^+-N浓度对土壤硝化反应速度及N_2O排放的影响

Effect of soil temperature,moisture and NH 4_+^-N concentration on nitrification and nitrification-induced N_2O emission

硝化反应是土壤、特别是干旱半干旱地区农业土壤N2O产生的重要途径之一。但是,目前环境条件对硝化反应中N2O排放的影响研究较少,而在国内外通用的几个模型中均用固定比例估算硝化反应过程中N2O的排放。本文通过砂壤土培养试验,研究了土壤温度、水分和NH4+-N浓度对硝化反应速度及硝化反应中N2O排放的影响,并用数学模型定量表示了各因素对硝化反应的作用,用最小二乘法最优拟合求得该土壤的最大硝化反应速度及N2O最大排放比例。结果表明,随着温度升高,硝化反应速度呈指数增长;水分含量由20%充水孔隙度(WFPS)增加到40%WFPS时,反应速度增加,水分含量增加到60%WFPS时反应速度略有降低;NH4+-N浓度增加对硝化反应速度起抑制作用。用米氏方程描述该土壤的硝化反应过程,其最大硝化反应速度为6.67mg·kg?1·d?1。硝化反应中N2O排放比例随温度升高而降低;随NH4+-N浓度增加而略有增加;20%和40%WFPS水分含量时,硝化反应中N2O排放比例为0.43%～1.50%,最小二乘法求得的最大比例为3.03%,60%WFPS时可能由于反硝化作用,N2O排放比例急剧增加,还需进一步研究水分对硝化反应中N2O排放的影响。

Nitrification is a major source of N2O.However,there is little information on how environmental and soil variables affect N2O emission during nitrification.A fixed fraction rate is often used to estimate N2O emission from soil induced by nitrification in most available models.To that end,an incubation experiment was conducted to investigate the effect of soil moisture,temperature and NH 4＋-N concentration on nitrification and nitrification-induced N2O emission in acidic sandy-loam soils in southeastern Australia.The Michaelis-Menten equation was used to express nitrification dynamics while the Least Square method was used to derive the maximum velocity of nitrification and N2O fraction of nitrification.A series of algorisms were proposed to describe the relationships between nitrification velocity/N2O production and the driving factors of NH 4＋-N concentration,soil moisture and temperature.Results show exponentially enhanced nitrification velocity with increasing soil temperature.Nitrification velocity increases when soil water-filled porosity （WFPS） increases from 20% to 40%,reaches its peak at around 40%,and then declines at 60% WFPS.NH 4＋-N concentration is negatively correlated with nitrification velocity.By fitting with Least Square,a maximum reaction velocity （V max） is achieved at 6.67 mg·kg-1 ·d-1 for the sandy-loam soil.N2O emission fraction of nitrification declines with increasing incubation temperature.Soil NH 4＋-N concentration is slightly positively correlated with soil nitrification emitted N2O.Under 20% and 40% WFPS,measured N2O emission fraction of nitrification range is 0.43%～1.50%,with a maximum fraction of 3.03% obtained by fitting Least Square.However,this method cannot reliably assess the impact of soil WFPS on N2O emission fraction of nitrification.,Bbecause N2O emission increases exponentially when WFPS increases to 60%,indicating that soil denitrification might occur at 60% WFPS.