华北落叶松人工幼、中龄林土壤肥力变化

2005年以北京市营盘附近中山20年生和28年生华北落叶松人工林为对象，通过测定土壤表层0～20 cm土壤物理性质、化学性质和土壤酶的季节动态，用主成分分析法探讨华北落叶松幼、中龄林土壤肥力的变化。结果表明:28年生华北落叶松人工林土壤含水量、最大持水量、毛管持水量和非毛管孔隙度等低于20年生华北落叶松，而土壤容重和毛管孔隙度高于后者；随林龄增大，华北落叶松土壤pH下降0.10个单位，土壤全氮、速效钾含量不同程度降低，而有效磷含量有一定升高；相对于20年生华北落叶松，除多酚氧化酶外，28年生华北落叶松土壤过氧化氢酶、转化酶、脲酶和碱性磷酸酶活性降低。土壤脲酶、过氧化氢酶、最大持水量、非毛管孔隙度是评价华北落叶松土壤肥力的重要指标。20年生华北落叶松林分土壤肥力对密度较敏感，应及时适量间伐。20、28年生土壤综合得分IFI分别为0.358和-0.358，营盘附近中山大面积栽植华北落叶松需持慎重态度。 

Changes of soil fertility in young and middle aged Larix principis-rupprechtii plantations.

In 2005，the dynamics of soil physiochemical properties and soil enzyme in the soil surface of 0-20 cm depth was manipulated in the 20- and 28-year-old Larix principis-rupprechtii plantations. Changes of soil fertility with forest age were analyzed by a comprehensive evaluation method. The authors found that the soil moisture content，the maximum soil moisture capacity，capillary moisture capacity and non-capillary porosity of the 28-year-old plantations were lower than those of the 20-year-old plantations，while the soil bulk density and capillary porosity of the 28-year-old plantations were higher. With the increase of forest age，the soil pH lowered by 010 unit， the content of total N and available K decreased and the content of available P increased slightly. Except for with polyphenol oxidase，the content of soil catalase，invertase，urease and alkaline phosphatase decreased in the 28-year-old in comparison with the 20-year-old plantations. Soil urease，catalase，the maximum soil moisture capacity and non-capillary porosity could be used as indicators to assess the soil fertility. The soil fertility in 20-year-old plantations was more sensitive to forest density and so feasible thinning intensity should be adopted in the plantations as soon as possible. The IFI (integrated fertility index) of the young and middle stands was 0.358 and –0.358，respectively. Therefore，planting L. principis-rupprechtii in a large scale should be cautious.