Abstract: Ecological security covers natural ecological security, economic ecological security, and social ecological security. The particular points of natural and semi-natural ecosystem security encompass the integrity and health of the ecosystem. Ecological security describes a state that the area, country, and even global ecological environment are not threatened, which may provide ecological guarantee for the sustainable development of whole ecological-economic system. To construct the comprehensive index system of ecological security assessment of Daling River watershed, a total of 28 indices were chosen from the aspects of ecological status, ecological press, and ecological effect. The results showed that the integrated assessment values of 1987 and 2002 were 7.48 and 7.51, respectively, indicating that the ecological security of Daling River watershed was well, whereas the ecological press of 2002 was increased by 32.5%, compared with that of 1987. The main reason of the constant ecological security of Daling River watershed was the implementation of catchment management, which made the ecological status and ecological effect of 2002 be 2.29 and 2.42 times higher than that of 1987, respectively.

Key words: Arbuscular mycorrhizal fungi, Potassium-applied amount, Potassium accumulation and distribution, Potassium content in tobacco leaf, Flue-cured Tobacco