松嫩草甸羊草（Leymus chinensis）群落、碱茅（Puccinellia tenuiflora）群落和虎尾草（Chloris virgata）群落土壤脲酶活性的季节动态呈单峰曲线变化，在土体中随土层的加深，其活性逐渐递减。各群落0～10 cm土层中的土壤脲酶活性与月平均降雨量呈幂函数关系，与土壤温度呈指数函数关系。土壤脲酶活性受多种土壤理化因子的共同影响，对于羊草群落，各因子的影响程度依次为：pH值>有机质>速效氮>C/N>容重>全氮>速效磷；碱茅群落为：有机质>C/N>全氮>容重>速效磷>速效氮>pH值；虎尾草群落为：全氮>有机质>速效氮>pH值>C/N>速效磷>容重。对该地区土壤肥力影响因子的主成分分析表明：有机质、全氮、速效氮、C/N和土壤容重对土壤肥力的贡献率占主导地位，土壤脲酶活性所占的比重较小，它不能完全反映土壤肥力状况。
The seasonal changes of soil urease activity appeared to produce single-peaked curves in Leymus chinensis, Puccinellia tenuiflora and Chloris virgata communities in the Songnen meadow. The activity became gradually lower with increasing depth of soil layers. Soil urease activity of the 0-10 cm layer had a power-function correlation to rainfall (monthly mean value) and an exponential correlation to soil temperature, which showed that urease activity was deeply influenced by water and heat factors. Path analysis between urease activity and soil physical-chemical factors showed that urease activity was the result of interactions among soil physical-chemical factors, and each factor acted differently in the three communities. In the L. chinensis community, soil physical-chemicalfactors affecting urease activity decreased in the order of pH > organic matter > available N > C/N ratio > soil bulk density > total N > available P. In the P． tenuiflora community, the order was organic matter > C/N ratio > total N > soil bulk density > available P > available N > pH. In the C． virgata community, the order was total N >organic matter> available N > pH > C/N ratio > available P > soil bulk density. The dominant influencing factors were also found in the three communities through stepping multi-regression. They were organic matter and pH in L． chinensis community, organic matter and soil bulk density in P．tenuiflora community and total N in C．virgata community, which showed that organic matter was the base of soil urease activity. Principal component analysis of the soil fertility indicated that the contribution of or ganic matter, total N, available N, C/N ratio and soil bulk density accounted for the most part, while the contribution of urease activity was low. That is why the soil urease activity of the C．virgata community, which grew in the barren region, was higher than that of the L．chinensis community, which grew in the fertile region in the Songnen meadow. Although the soil urease activity was remarkably correlated with most of the soil physical-chemical factors, it only dealt with the nitrogen transformation among many soil nutritional element transformations. Therefore, soil urease activity does not completely reflect the conditions of soil fertility but is only an assistant index for evaluation.
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