林分类型和氮添加对亚热带森林土壤氧化亚氮排放的影响

为揭示亚热带森林土壤N₂O排放对林分类型和氮添加的响应特征，选取位于福建省三明市的中亚热带米槠次生林、杉木人工林和马尾松人工林土壤为研究对象，分别设置无氮添加(N0 mg/kg)、低氮添加(N10 mg/kg)、中氮添加(N25 mg/kg)和高氮添加(N50 mg/kg)4个氮添加水平，进行微宇宙培养试验，测定土壤N₂O排放。结果表明：与无氮添加处理相比，氮添加整体上降低3种林分土壤pH,增加土壤NH₄⁺-N和NO₃^--N含量。无氮添加处理中杉木人工林和马尾松人工林土壤N₂O累积排放量分别为9.67和9.62 mg/kg,显著高于米槠次生林土壤N₂O累积排放量6.81 mg/kg。低氮添加处理中杉木人工林和马尾松人工林土壤N₂O累积排放量显著高于米槠次生林。但在中氮和高氮添加处理中，3种林分土壤N₂O累积排放量均无显著性差异。不同氮添加处理均促进3种林分土壤N

Effects of Forest Types and Nitrogen Addition on Soil Nitrous Oxide Emissions in a Subtropical Forest

To reveal the response of soil N₂O emissions to forest types and nitrogen addition in subtropical forests, soil samples were collected from Castanopsis carlesii secondary forests, Cunninghamia lanceolata plantation and Pinus massoniana plantation located in Sanming City, Fujian Province. A microcosm was carried out and the soils were amended with NH₄NO₃ at four levels: no nitrogen addition (N0 mg/kg), low nitrogen addition (N10 mg/kg), medium nitrogen addition (N25 mg/kg) and high nitrogen addition (N50 mg/kg) to determine N₂O flux. The results showed that nitrogen addition generally decreased soil pH, while increased soil NH₄⁺-N and NO₃^--N contents. The cumulative N₂O emissions in C. lanceolata and P. Massoniana plantations with no nitrogen addition were 9.67 and 9.62 mg/kg, respectively, and were significantly higher than 6.81mg/kg in C. carlesii secondary forest. Similar trend was found in soils with low nitrogen addition. However, in the medium and high nitrogen addition treatments, there were no significant differences in cumulative N₂O emissions among the three forest stand types. Nitrogen addition increased soil N₂O emission in all the three forest types, with the effect size of low nitrogen addition on N₂O emissions in secondary forest soil being 0.01, significantly lower than the effect size of 0.45 in C. lanceolata and P. massoniana plantation soils. Conversely, the effect sizes of medium and high nitrogen additions on N₂O emission were significantly higher in secondary forests than plantations. These results indicated that N₂O emissions in secondary forests was more likely to be stimulated by medium or high nitrogen addition. Cumulative N₂O emissions were positively associated with soil NH₄⁺-N and NO₃^--N contents (p<0.01), rather than soil pH, indicating that available nitrogen was the main factor controlling soil N₂O emissions in forest soils under nitrogen additions. Taken together, N₂O emissions were higher in plantation soils than in secondary forest soil, but N₂O emissions in secondary forests soil were more sensitive to medium and high nitrogen additions.