设施菜田土壤剖面中的反硝化特征

利用田间原位硅胶管法和自动连续在线培养监测体系（Robot 系统），分别监测了设施菜田不同施肥处理土壤剖面N2O浓度以及不同土层土壤反硝化潜势、NO和N2O产生潜势。结果表明:灌溉施肥后，传统施肥处理（CN）土壤剖面50 cm和90 cm处的N2O浓度都会出现峰值，50 cm处的N2O浓度峰值都高于90 cm处； 50 cm处的N2O变幅在2.15～50.77 l/L 之间，90cm处的变幅在2.57～14.05 l/L 之间；空白处理（CK）剖面N2O浓度几乎不受灌水的影响，50 cm和90 cm处的N2O浓度变幅较小，在1.43～2.75 l/L 之间。反硝化潜势、NO和N2O产生潜势的监测结果显示，040 cm土层反硝化较为强烈；40100 cm土层中由于受碳源限制，反硝化发生及强度明显滞后，添加碳源，经过48 h培养后，能够达到与表层反硝化潜势相当的程度；厌氧条件下，上层040 cm土壤的N2O和NO产生量远高于底层40100 cm的。由此推测，原位监测的高N2O浓度，可能来源自上层的扩散，因而田间表层通量观测数据可能会低估N2O产生量。底层土壤有一定反硝化潜势，当施用有机肥后，底层土壤氮素反硝化损失不容忽视。

Characteristics of denitrification in different soil layers in a greenhouse vegetable cropping system

Silicone tubes installed at 50 cm and 90 cm respectively in situ were applied to monitor concentrations of N2O in soil profile in a greenhouse tomato cropping field,and a robotized incubation system was used to measure potential production of N2O,NO and denitrification.The results show that the occurrences of the N2O peaks at the depths of 50 cm and 90 cm were just after irrigation/fertilization under the conventional N treatment(CN),and the N2O concentration at the depth of 50 cm is higher than that at the depth of 90 cm,varying from 2.15 to 50.77 μL/L at 50 cm,and from 2.74 to 14.05 μL/L at 90 cm.Under the control treatment(CK),the N2O concentrations at both depths are almost not affected by irrigation,varying from 1.43 to 2.75 μL/L.Denitrification mainly occurres in the layer of 0-40 cm,and due to carbon limitation,denitrification in the layer of 40-100 cm is relatively weak.However,after 48 hours incubation with carbon addition,denitrification in the lower soil layer shows a similar denitrification potential as the surface soil.Under anaerobic conditions,the N2O and NO emissions from the upper layer(0-40 cm) are much higher than those of the lower layer(40-100 cm).High N2O concentrations are observed at the 50 and 90 cm in situ,might be diffused from the surface soil.Therefore,field flux measurements might underestimate the N2O emission.Since the lower layer has similar denitrification potential as the surface soil,denitrification loss should not be ignored under the conditions with leaching of both nitrate and organic carbon.