Abstract:

In 2000, the effect of thinning intensities with five different treatments of 0%(CK), 30%(slight thinning), 48.75%(middle thinning),53.75%(intense thinning) and 65.6%(super intense thinning) on the soil enzyme were carried out in the 9-year-old aerial seeding Pinus tabulaeformis stands with initial density of 8 000 trees·hm^-2, in QingQuanPu Aerial Seeding Center, Yanqing County of Beijing Municipality. Five years later, the activities of the five soil enzymes such as soil urease, alkaline phosphatase, inertase, catalase and polyphenol oxidase in the different soil layers of A(0～20 cm), B(20～40 cm) and C(40～60 cm) were compared. Moreover, relationships among soil enzymes, soil physiochemical properties and the diversity of the undergrowth were analyzed to prove the availability of using soil enzymes to evaluate the thinning intensities. The results showed that soil catalase varied slightly while the other four soil enzymes decrease with increasing soil depth. And the soil enzymes in the layer A were enhanced distinctly compared with in the layers B and C. Also, the five soil enzymes in the layer A were affected differently by thinning intensities, showing that soil urease and alkaline phosphatase were highest response to slight thinning followed by the middle thinning, opposite to the trend of inertase and polyphenol oxidase. There are significantly positive relationships between soil enzymes and soil physiochemical characteristics and the organic C and total N was more dominant than available K as well as available P. Except soil polyphenol oxidase, the other soil enzymes showed positive relationships with biodiversity of the undergrowth. It was concluded that reasonable thinning intensity was benefit to the development of the undergrowth and so can be to soil enzymes. Generally, when the stand with initial density of 8 000 trees·hm^-2 grows up to 9 years old, the reasonable thinning intensity should be about 48.75%.

Key words: Pinus tabulaeformis, aerial seeding stands, thinning intensity, soil enzyme, soil nutrient, biodiversity