不同灌溉量对华北平原菜地N2O排放及其来源的影响

以华北平原菜地为研究对象,通过控制灌溉量设置不同的土壤水分对照,利用稳定同位素¹⁵N自然丰度法,结合传统的乙炔抑制试验,对不同土壤水分条件下的N₂O排放、N₂O同位素特征值以及同位素异位体位嗜值(SP值)变化规律进行分析,以阐明不同水分条件下N₂O的排放规律及其来源.结果表明:水分条件显著影响N₂O排放,相比于50%土壤孔隙含水率(WFPS),70%WFPS的水分条件下N₂O的排放较高.N₂O的排放集中在施肥前期,在施肥中后期迅速减弱.50%WFPS条件下,N₂O的排放最初以硝化作用为主,占比约为90%,随后硝化作用迅速下降,反硝化变成主导作用,施肥7 d后即达到80%以上;而70%WFPS条件下初期则以反硝化为主,占比约为70%,随后下降至40%左右,施肥10 d后逐渐升高至80%.整体上,N₂O的排放主要以反硝化作用为主,不同水分处理对土壤硝化、反硝化作用的影响主要体现在施肥前期,后期均以反硝化为主.综上,建议华北地区的菜地生产应适当降低灌溉量,以减少N₂O排放.

Effects of soil water condition on N2O emission and its sources in vegetable farmland of North China Plain

To understand the mechanisms of agricultural N₂O emission, we investigated the N₂O emission dynamics, the N₂O isotope signatures, and the site preference value under different soil water conditions in the vegetable farmland of North China, by using the stable isotope technique and the acetylene inhibition method. The results demonstrated that N₂O emission was significantly affec-ted by the water condition, and N₂O emissions from soil with water-filled pore space (WFPS) of 70% were significantly higher than that with 50% WFPS. N₂O emission occurred mostly in the early stage of fertilization, and decreased rapidly in the later stage of fertilization. At 50% WFPS, nitrification was the major process generating N₂O during the early fertilization stage, accounting for approximately 90% of the N₂O emission. However, the contribution of nitrification decreased sharply, whereas denitrification became the dominant process, accounting for 80% of the N₂O emission 7 days after the fertilization. On the other hand, at 70% WFPS, denitrification was the main process releasing N₂O during the early fertilization stage, decreasing from 70% to 40% and then gradually increasing to 80% 10 days after the fertilization. Overall, N₂O emission was mainly dominated by the denitrification. The effect of different water treatments on soil nitrification and denitrification took place mainly in the early stage of fertilization, and N₂O emission was gradually dominated by the denitrification at the later stage. These results suggested we could reduce N₂O emission by approp-riately reducing the amount of irrigation in the vegetable farmland of North China.