Abstract: Thinning is an important forest management practice promoting tree growth and influencing soil properties in plantations, especially for soil microorganisms and enzyme activities. The objective of this study was to determine the effects of different thinning intensities on soil enzyme activities in Larix kaempferi plantations. This study was conducted in two different site conditions (high or low soil fertility) in the montane region of eastern Liaoning Province of Northeast China. The thinning treatments included control treatment, 25% and 50% thinning intensity. The results showed that the phenol oxidase activity was higher in autumn season than in other seasons, while the activities of exoglucanase, β-glucosidase, N-acetyl-β-glucosaminidase, acid phosphatase were higher in spring season than in summer and autumn seasons at the two sites. In addition, the 25% thinning treatment significantly increased the activities of phenol oxidase and Nacetylβ-glucosaminidase in the 0-10 cm soil layer, whereas 25% and 50% thinning treatments decreased the activities of β-glucosidase, N-acetylβvglucosaminidase, acid phosphatase in the 10-20 cm soil layer at the low soil fertility site. There were significant positive correlations between enzyme activities and soil total carbon, total nitrogen and inorganic nitrogen when all samples were pooled together. In contrast, these studied enzyme activities were negatively correlated with soil pH. Especially, the correlations between soil enzyme activities and inorganic nitrogen decreased in the 25% thinning treatment at the low soil fertility site. In addition, the correlations between soil enzyme activities and soil total carbon, available phosphorus also decreased, while the correlations between soil enzyme activities and soil total phosphorus increased in the 50% thinning treatment at the high soil fertility site. In conclusion, to improve the soil enzyme activities, 25% and 50% thinning intensity should be conducted in Larix kaempferi plantations with low and high soil fertility, respectively.

Key words: carbon emission reduction, oasis irrigation area, cropping pattern, economic benefits, resource utilization, emergy analysis