秦岭西部中幼龄华北落叶松林地土壤养分与酶活性特征研究

【目的】作为最重要的速生造林树种,50多年前华北落叶松就被引入陕西并造林,引种初期华北落叶松生长良好,而近年来生长势明显下降,地力衰退问题也日益受到关注。本文研究了秦岭西部中幼龄华北落叶松林地土壤养分与酶活性特征,以期为华北落叶松幼龄期人工林的合理经营、中幼龄林地土壤生态系统结构、功能及其可持续利用提供科学依据。【方法】本试验选取立地条件基本一致的5 a、10 a和20 a的华北落叶松人工林地,每个样地设置20 m×20 m的标准地,用土钻在每个标准地沿"S"型采集5个点的0—20 cm、20—40 cm和40—60 cm的土样,各层混均,用四分法取样,分析不同林龄华北落叶松人工林地土壤剖面的p H值、有机质及氮、磷养分和酶活性。【结果】研究结果表明,土壤p H值在5 a林地随土壤深度的增加逐渐升高,而在10 a和20 a林地表现为先降低后显著升高(P0.05),不同林龄林地0—20 cm土层的p H值变化范围为6.21~6.71,表现为10 a5 a20 a;40—60cm和20—40 cm土层均表现为5 a10 a20 a。不同林龄林地的表层(0—20 cm)土壤有机质含量变化范围为18.68~25.89 g/kg,均显著高于下层(20—40 cm和40—60 cm)土壤,随着林龄的增加没有明显的变化趋势。土壤全氮、硝态氮、铵态氮和速效磷含量随着土壤深度的增加呈明显下降的趋势(P0.05),而在0—20 cm土层中,20 a林地的氮含量显著高于5 a和10 a林地的(P0.05),10 a林地的速效磷含量最高。不同林龄的土壤蔗糖酶、脲酶和磷酸酶活性在0—20 cm土层显著高于20—40 cm和40—60 cm土层(P0.05),过氧化氢酶活性却呈相反的变化趋势。0—20 cm土层,不同林龄林地的蔗糖酶和脲酶活性表现为10 a5 a20 a,磷酸酶和过氧化氢酶活性在20 a林地土壤中最大,不同林龄林地土壤蔗糖酶、脲酶、磷酸酶和过氧化氢酶活性的变化范围分别为25.93~71.07Glucose mg/g、0.15~0.52 NH3-N mg/g、0.28~0.41 Phenol mg/g和3.95~4.58 m L 0.01 mol/L KMn O4/g。相关性分析表明,土壤有机质、全氮和速效磷含量与土壤蔗糖酶、脲酶和磷酸酶活性呈极显著的正相关性(P0.01),与过氧化氢酶呈极显著的负相关性(P0.01)。【结论】华北落叶松的生长对土壤p H、有机质、全氮、硝态氮、铵态氮和速效磷的变化产生了明显影响,同时也影响了土壤酶活性;由于该地区土壤的有效氮和速效磷含量较低,加上林木的快速生长,20 a华北落叶松林地力呈现衰退趋势。基于以上研究结果,建议在该地区对于接近20 a的华北落叶松人工林地采取施肥措施,以补充土壤养分,保证林木的正常生长。

Characteristics of soil nutrients and enzyme activities in young and middle aged Larix principis-rupprechtii plantation in western Qinling Mountains

【Objectives】 As one of the most important fast-growing afforestation tree species, Larix principis-rupprechtii has been introduced to Shaanxi Province fifty years ago.They grew well in early age, but with the age increased, the growth rate obviously slowed down.So, we studied the characteristics of soil nutrients and enzyme activities in young and middle aged Larix principis-rupprechtii plantation in western Qinling Mountains.【Methods】 We chose three different aged Larix principis-rupprechtii (5 a,10 a and 20 a) plantations in the Nantan Nursery Garden of Taibai in Shannxi Province as the experimental sites, and established 20 × 20 m plot in each age stand plantation in 2012. In each plot, soil samples were collected at three depths(0-20 cm, 20-40 cm, and 40-60 cm) in five randomly located points following “S”. Using these samples, we examined soil chemical properties (pH, organic matter, total N, ammonium N, nitrate N and available P) and enzyme activities (phosphatase, urease, invertase, and catalase) in the different age of plantations.【Results】 With the soil depth increased, the soil pH values are increased in 5 years plantations, but decreased first and then significantly increased (P0.05) in 10 and 20 years plantations. The soil pH range from 6.09 to 6.71, in order of 10 a 5 a 20 a in 0-20 cm layer, and 5 a 10 a 20 a in 20-40 cm and 40-60 cm layers. The contents of soil organic matter in 0-20 cm layer range from 18.68 to 25.89 g/kg, significantly higher than in 20-40 cm and 40-60 cm layers, and keep constant as the planting age increased. There are significant reductions (P0.05) in soil total N, ammonium N, nitrate N and available P nutrients as the soil depth increased. In 0-20 cm layer, the contents of soil total N, ammonium N and nitrate N in 20 years plantations are significantly higher (P0.05) than those in other-aged plantations. The soil available P in 10 years plantations is highest. The activities of soil invertase, urease and phosphatase in 0-20 cm layer are significantly higher (P0.05) than those in 20-40 cm and 40-60 cm layers, while the soil catalase activities show an opposite tendency. In the 0-20 cm soil layer, the activities of soil invertase and urease in different years plantation show as 10 a 5 a 20 a, the activities of soil phosphatase and catalase in 20 a-aged plantations are the highest, the variation ranges for these activities are as follows: invertase, 25.93-71.07 Glucose mg/g; urease, 0.15-0.52 NH3-N mg/g; phosphatase, 0.28-0.41 Phenol mg/g and catalase 3.95-4.58 mL 0.01 mol/L KMnO4 /g.【Conclusions】 The growth of Larix pricipis-rupprechtii affects the physichemical and biological properties of soil. Because of the lack of soil available N and available P in this area and the rapid growth of plants, the fertility of plantations in the Qinling Mountains become worse when Larix principis-rupprechtii grow over 20 years. Accordingly, fertilizer should be applied in these plantations in order to avoid nutrient limitation for plant growth.