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.