Abstract: The aim of this study was to evaluate the effects of different silvicultural ways on soil fertility in the larch plantation. One 22-year-old larch stand was chosen and treated with four treatments (control treatment: 900 trees·hm^-2, medium thinning treatment: 750 trees·hm^-2, heavy thinning treatment: 450 trees·hm^-2, clear cutting treatment: 0 tree·hm^-2). Soil nutrients, soil enzyme activities in the top (0-10 cm) and subtop (10-20 cm) soil layers and their relationships were analyzed. Our results showed that (1) compared with the control, total carbon and total phosphorus in the top soil layer, and total carbon, total nitrogen, total phosphorus, and pH in the subtop soil layer significantly decreased in the heavy thinning treatment. In addition, total phosphorus in the top soil layer and total nitrogen and total phosphorus in the subtop soil layer significantly decreased after clear cutting. The heavy thinning and clear cutting treatments did not significantly change soil available phosphorus and inorganic nitrogen contents. (2) Compared with the control, the activities of phenol oxidase, exoglucanase and N-acetyl-β-cosaminidase significantly increased in the top soil layer under the medium thinning treatment, while acid phosphatase activity significantly decreased in the top and sub-top soil layers under the heavy thinning treatment and in the top soil layer under the clear cutting treatment. (3) Compared with the control, the specific enzyme activities (i.e., normalized to soil total C and N), including phenol oxidase, exoglucanase, β-glucosidase, and N-acetyl-β-glucosaminidase, significantly increased in both two studied soil layers under the medium and heavy thinning treatments. How-ever, there were no significant differences in phenol oxidase, exoglucanase, β-glucosidase, and N-acetyl-β-glucosaminidase activities between the control and clear cutting treatments, except for the phenol oxidase activity. (4) The results of correlation analyses showed that the studied enzymes were significantly related to total carbon, total nitrogen, total phosphorus, and inorganic nitrogen contents. In conclusion, medium thinning was more advantageous to sustaining soil fertility in the larch plantation.

Key words: low magnesium stress, low temperature, chlorophyll, photosynthesis, Cucumis sativa.