中文摘要：

以华北平原区4个农田生态系统[京郊蔬菜大棚（GH）和河北栾城（LF）、河北南皮（NF）、山东惠民（HF）3个粮田]为研究对象,采用室内好气、恒温、避光条件下培养30 d,对比研究了不同海拔和不同农业扰动强度下的农田生态系统中耕层（0-20 cm）土壤的净N矿化、净硝化、净C矿化以及尿素的转化,旨在探索人类农业扰动强度和地理海拔对土壤供N潜力和尿素N转化的影响。结果表明,4个地区的土壤供N潜力分别为：14.4、13.2,17.7和16.5 mg/kg,说明高度熟化的华北区农田土壤供N潜力相对稳定。以施用有机肥为主的蔬菜大棚和以施用化肥为主的粮田对土壤供N没有显著影响。农田土壤净矿化后的供N形式主要是NO3^- -N。以施用有机肥为主的蔬菜大棚积累了较高的土壤有机质和全N,但是土壤净C矿化以及施用尿素后CO2的排放量均低于以施用化肥为主的粮田。尿素在各区域农田土壤中水解转化后均主要以NO3^- -N形式存在,NO3^- -N占尿素水解后无机N增量的98%9-9%;华北平原农田生态系统施入尿素态N 30d后,水解成有效态无机N的转化率为63.4%8-3.2%,即每克尿素态N在京郊蔬菜大棚（GH）、栾城高产农田（LF）、南皮农田（NF）和惠民农田（HF）土壤中转化为NO3^- -N的量分别为0.69、0.82、0.64和0.63 g/kg,同时可使相应区域农田的CO2排放量分别增加CO21.20、1.360、.67和1.58 g/kg。

英文摘要：

To compare soil N supply capacity, urea transformation and nitrification in four regions of the North China Plain under intensive anthropogenic disturbance, we measured soil net N and C mineralization, nitrification and urea transformation in green house （GH） and field agroecosystems across elevation and fertilization gradients, namely, Luancheng （LF）, Nanpi （NF） and Huimin （SF）, by using 30d laboratory aerobic incubation. We found that net nitrification were positively correlated with net mineralization, indicating that the increase of NO3^- -N was the main result of net mineralization. The soil N supply capacity did not differ in North China Plain where the soils are highly disturbed and heavily fertilized with N. There were no significant differences in soil net mineralization and net nitrification either between manure and chemical fertilizer input, or among the regions in North China Plain. The soil net mineralization was 14.4, 13.2, 17.7 and 16.5 mg/kg during 30d incubation for GH, LF, NF and HF, respectively. However, Net C mineralization of GH, which was subjected to heavy manure application, was significantly lower than that in other three regions during incubation period. NO3^- -N was increased after urea hydrolysis, and about 63.4%-83.2% of urea-N was transformed to inorganic N in North China Plain, with the rate of urea transformation being significantly different among the four regions. 1 g of applied urea - N invoke a net nitrification increase of about NO3^- -N 0. 69, 0. 82, 0. 64 and 0.63g/kg, and CO2 1.20, 1.36, 0.67 and 1.58 g/kg for GH, LF, NF and HF, respectively.