中文摘要：

以小兴安岭湿地土壤为研究对象,基于冻融模拟试验和室内分析,对比研究了不同冻融环境下土壤溶解性有机碳（DOC）含量变化趋势及其氮素矿化特征。结果表明：无论是（-5）~5℃还是（-25）~5℃冻融处理,天然兴安落叶松湿地、灌丛湿地以及2003年,1992年排水造林后兴安落叶松湿地4种土壤的DOC含量均差异显著（P〈0.01）,且随着冻融次数的增加,土壤DOC含量均呈现先增加后减小的趋势,1次冻融循环后达到最大值,其平均含量分别为580.05 mg/kg,546.11 mg/kg,475.38 mg/kg,423.52mg/kg,表明冻融作用对土壤DOC短期效应明显。冻融次数对2003年排水造林后湿地土壤DOC含量影响极显著（P〈0.01）,而对1992年排水造林后湿地土壤DOC含量影响显著（P〈0.05）。土壤铵态氮含量先增加后减少,2次冻融循环后达到最大值,其平均含量分别为68.92mg/kg,53.34mg/kg,21.57mg/kg,22.09mg/kg,而土壤硝态氮含量先减少后增加,1次冻融循环后达到最小值,其平均含量分别为4.86mg/kg,3.91mg/kg,10.62mg/kg,10.10mg/kg,但（-25）~5℃比（-5）~5℃冻融处理的氮矿化程度高,表现出冻融循环能够促进氮素矿化,且较大的冻融温差更能加速矿化进程。

英文摘要：

In order to explore the content changes of dissolved organic carbon（DOC）and the characteristics of nitrogen mineralization in wetland soil in different freeze-thaw environment,the research was conducted based on the freezing and thawing simulated experiments and indoor analyses of the wetland soil in Xiaoxing＇an Mountains.In both（-5）~5 ℃ and（-25）~5 ℃ freeze-thaw treatments,DOC contents of natural Larix gmelini wetland,shrub wetland,and larix gmelini wetland after drainage and afforestation in 2003 or 1992showed significant difference（P〈0.01）.With the number of freeze-thaw cycles increasing,DOC content rose up at first and then declined in both（-5）~5 ℃ and（-25）~5 ℃ freeze-thaw treatments.DOC content peaked after 1freeze-thaw cycle,and the average DOC contents of 4types of soil were 580.05mg/kg,546.11mg/kg,475.38mg/kg,and 423.52mg/kg,respectively,which indicated that the effect of freeze-thaw action on DOC content in soil was obvious in short period.The number of freeze-thaw cycles had extremely significant effect on DOC content in soil after drainage and afforestation in 2003（P〈0.01）,while it also had significant impact on DOC content in soil after drainage and afforestation in 1992（P〈0.05）.In addition,the trend of ammonium nitrogen content increased at first and then decreased,which reached the maximum value after 2freeze-thaw cycles,and the average ammonium nitrogen contents of 4types of soil were 68.92 mg/kg,53.34 mg/kg,21.57 mg/kg,and 22.09 mg/kg,respectively.However,the nitrate nitrogen showed the opposite trend and reached the minimum value after 1freeze-thaw cycle.In 4types of soil,the average contents of nitrate nitrogen were 4.86 mg/kg,3.91 mg/kg,10.62 mg/kg,and 10.10 mg/kg,respectively.In（-25）~5℃freeze-thaw treatment,nitrogen mineralization was higher in degree,compared to that in（-5）~5℃freeze-thaw treatment,suggesting that freeze-thaw cycle could promote nitrogen mineralization,and the larger differences of freezing and thawing temperatures cou