在内蒙古贝加尔针茅草原，分别设对照（N0）、1.5 g·m-2（N15）、3.0 g·m-2（N30）、5.0 g·m-2（N50）、10.0 g·m-2（N100）、15.0 g·m-2（N150）、20.0 g·m-2（N200）和30 g·m-2（N300）（不包括大气沉降的氮量）8个氮素（NH4NO3）梯度和模拟夏季增加降水100 mm的水分添加交互试验，研究氮素和水分添加对草原土壤养分、酶活性及微生物量碳氮的影响。结果表明：氮素和水分添加对草原土壤理化性质和生物学特性有显著影响。随施氮量的增加土壤总有机碳、全氮、硝态氮、铵态氮含量呈增加的趋势，相反，土壤pH值呈降低的趋势。土壤脲酶和过氧化氢酶的活性随施氮量的增加而升高，多酚氧化酶则随施氮量的增加呈下降的趋势。氮素和水分添加对草原土壤微生物量碳氮含量有显著影响，高氮处理（N150、N200和N300）显著降低了微生物碳含量，微生物氮含量随施氮量的增加呈上升趋势。水分添加能够减缓氮素添加对微生物的抑制作用，提高微生物量碳、微生物量氮含量。草原土壤养分、土壤酶活性及土壤微生物量碳氮含量间关系密切，过氧化氢酶与全氮、总有机碳、硝态氮呈显著正相关，多酚氧化酶与铵态氮、硝态氮、全氮呈显著负相关。微生物量氮含量与土壤全氮、铵态氮、硝态氮含量以及过氧化氢酶和磷酸酶活性呈显著正相关，与多酚氧化酶呈负相关；微生物量碳与过氧化氢酶呈负相关，与多酚氧化酶活性呈正相关。%In this paper, eight nitrogen treatments were applied at 0 g·m-2(N0), 1.5 g·m-2(N15), 3.0 g·m-2(N30), 5.0 g·m-2(N50), 10.0 g· m-2(N100), 15.0 g·m-2(N150), 20.0 g·m-2(N200), 30.0 g·m-2(N300)as NH4NO3 and adding water to simulate summer rainfall of 100 mm, the interactive experiment was set to explore the effects of nitrogen and water addition in Stipa baicalensis steppe on soil nutrients, enzyme activities and soil microbial biomass. The results showed that the nitrogen and water addition changed soil physico-chemical factors obvious-ly, the content of soil total organic carbon, total nitrogen, nitrate nitrogen and ammonium nitrogen increased along with the increasing of ap-plication rate of nitrogen, on the contrary, the soil pH value had decreasing trend. Appropriate application of nitrogen could enhance the ac-tivity of urease and catalase but decreased the activity of polyphenol oxidase. Nitrogen and water addition had significant effect on soil micro-bial biomass C and N. Higher level of N fertilizer significantly reduced microbial biomass C, and the microbial biomass N was on the rise with the application rate of nitrogen. The addition of water could slow the inhibition of nitrogen to microorganism and increase the microbial biomass C and N. A closed relationship existed in soil nutrient, activities of soil enzyme and soil microbial biomass C and N. The significantly positive correlation existed between total N, organic C, nitrate N and catalase, significantly negative correlation between nitrate N, ammonium N, total N and polyphenol oxidase. Microbial biomass N was significantly positive correlated with total N, nitrate N, ammonium N, catalase, phosphatase, and was negative correlated with polyphenol oxidase. Microbial biomass C was significantly positive correlated with polyphenol oxidase, and was negative correlated with catalase.
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