关键词: 生态足迹, 生态承载力, 生态盈余, 西藏农牧民

Abstract: We examined the effects of Cupressus funebris root exudates on soil nutrients and enzyme activities in the mixed plantation of C. funebris and Toona sinensis with a potculture method. The C. funebris root exudates were collected by soil culture method and added to the potted seedlings of T. sinensis every month. Four treatments of G1, G2, G3 and G4 were set up, corresponding to the treatments with rhizosphere soil extracts of 1, 2, 4, and 8 cypresses respectively. Meanwhile, a control was treated with distilled water. After one year, the nutrient concentrations and enzyme activities of soil in the five groups were measured. The results showed that C. funebris root exudates had no effect on the concentrations of soil total N, total P and total K (P>0.05), but significantly increased the concentrations of alkalihydrolysable N, available P and available K (P<0.05). The concentrations of alkalihydrolysable N, available P and available K increased with increasing concentration of the extracts, with no difference between G3 and G4 (P>0.05). The activities of urease, neutral phosphatase, catalase and invertase in soil were boosted after adding root exudates, which were increased with increasing concentrations of exudates. The results of correlation analysis showed that the activities of the four enzymes were remarkably correlated with the concentrations of soil alkalihydrolysable N, available P, available K and pH (P<0.01), but had no relationship with that of total N, total P, and total K (P>0.05). There was a positive correlation among the activities of the four enzymes (P<0.01). Our results indicated that increasing concentration of C. funebris root exudates could increase the concentrations of alkalihydrolysable N, available P and available K, and enhance the activities of soil urease, neutral phosphatase, catalase and invertase, which would directly or indirectly affect theavailability of soil nutrients. The root exudates of four cypresses had the strongest effects on soil available nutrients and soil enzyme activities. When the mixing ratio ofC. funebris and T. sinensis was 4∶1, the soil environment could be much improved.

Key words: ecological footprint, ecological carrying capacity, ecological surplus, Tibetan farmers and herdsmen.