[English version] Based on the studies in the past 4 decades, Huitong Experimental Station of forest Ecology, the Chinese Academy of Sciences continues to work on the mechanism of soil degradation under Chinese fir plantation forest and its ecological restoration processes with the purpose of sustainable management of plantation forest. The achievements obtained in the past 5 years are listed as follows. 1. Ecology of tree roots The fine roots in different layer of soil under Cunninghamia lanceolata plantation and its mixed plantation with Michelia macclurei was examined by using soil core drill. The results showed that the turnover of fine roots and nutrient return in the mixed plantation forest was higher than that in pure plantation forest. There was a significant difference in nutrient content in fine roots between the two species in the mixed forest, indicating the possibility of translocation of nutrient, such as N and K, through fine roots cross the species. Compared with the first rotation of C. lanceolatat plantation, the distribution of fine roots in the top 10 cm soil and the concentration of H2PO4－ in exudates from fine roots under replanted C. lanceolata plantation forest decreased, which might be an important part of causes for the degraded growth of the trees. It has been proved that fertilization can enhance the growth of fine roots of the C. lanceolata. 2. Nutrient Cycling With the help of litter bags, we studied both the decomposition of and nutrient return of C. lanceolata, Alnus cremastogyne, Kalopanax septemlobus , M. macclurei, Cinnamomum camphora, Shima superba and Castanopiss hystrix was studied by using litter bags. The results showed there exists relatively lower N concentration and higher C/N ratio in Chinese fir needle litter. This was the critical factor in leading to slow decomposition of the litter, which cause soil depletion when replanting Chinese fir plantation for over two rotations. The studies on the decomposition of Chinese fir litter in mixture with broad-leaved species showed that not all broad-leaved species had enhancing effects on decomposition of Chinese fir litter and some species even had negative effect. It was suggested that an understanding of decomposition process in mixed litter would be helpful in making choice of tree species to plant with C. lanceolata. The decomposition of Chinese fir litter was enhanced by the fertilization with NO3--N, but not by the fertilization with NH4+-N. Effects of various combination of foliar litter from 4 tree species on the growth of the pot-cultured Chinese fir seedling and the availability of (15NH4)2SO4 was also examined. The result showed that there were significant positive growth responses to the increasing diversity of foliar litter species. In addition, the residue of (15NH4)2SO4 was greater in soil with foliar litter treatment than in soil without foliar litter. Both of the residual amount of (15NH4)2SO4 in soil and the total recovery rate of (15NH4)2SO4 increased with the increasing species diversity of applied foliar litter. 3. Chemical Ecology The decomposition and allelopathy of stump-roots of Chinese fir left from clear cutting were studied first in China. The concentration of phenolic substances, a major allelopathic substances, in Chinese fir stump-roots, in soil surrounding the stump-roots, and in bulk soil was also analyzed. The concentration of phenolics in the stump- roots decreased as the decomposition deepened, it was higher in surrounding soil than in bulk soil, and in Chinese fir plantation soil than in the soil under evergreen broadleaved forest. The number of stump-roots left on the site was found to be negatively correlated with the growth of young Chinese fir on the site. It can be inferred that the stump-roots are harmful to the growth of young Chinese fir plantation of the following rotation because decomposing stump-roots release phenolics substances and produce allelopathic effects. And the root-soil ecoboundary processes and chemi-allelopathy of root exudates were also examined. The results showed that the root exudates from three different stands all had chemi-allelopathy to the germinant growth of C. lanceolata seed, the root exudates from the stands of the first and second rotation had stronger chemo-allelopathy than that from the mixed stands of C. lanceolata with M. macclurei. A simulation experiment showed that vanillin and P-hydroxybenzoic acid decreased the availability of N and K in the treated soil and inhibited the root activity, which would reduce the uptake of the nutrients by the roots. In addition, the nitrogen distribution in different organs of seedlings was detected by 15N to be affected by the treatment of vanillin. 4. Soil Ecology We examined the ecological restoration processes and regulation mechanism of the degraded Chinese fir plantation soil. The results showed that the soil organic matter accumulation was enhanced significantly by mixed or rotated hardwood species from the zonal forest community. We concluded that the accumulation of soil organic matter and improvement of its composition are the key processes in the ecological restoration of degraded Chinese fir plantation soil. A significant difference was also found between the restoration rate of the major soil properties. A soil management approach with core management of soil organic matter was proposed for plantation soil as suggested by our research. Within the same period, 56 papers have been published in domestic core journals, and 2 in SCI journals. A monography on ecology of Chinese fir plantation and a special issue of Chinese Journal of Applied Ecology have also been published. In addition, the station successfully established a 600hm2 of demonstrative forest, playing a positive role in generalizing the optimized model of sustainable management of Chinese fir plantation.