Abstract: A field experiment was conducted to study the growth of Fritillaria thunbergii Miq. and the physicochemical properties, microbial flora, and enzyme activities of rhizosphere soil under 1-, 2-, and 4-year cropping, aimed to reveal the possible mechanisms of continuous cropping obstacle of F. thunbergii. With the increasing duration of continuous cropping, the contents of soil available N, P, and K decreased significantly while that of soil organic matter increased, soil pH presented a decreasing trend, the total amount of soil microbes and the amounts of soil bacteria and actinomycetes decreased linearly whereas the amount of soil fungi had a linear increase, and the activities of soil urease and catalase decreased but those of soil polyhenol oxidase and saccharase were in adverse. Under continuous cropping, the F. thunbergii membrane lipid peroxidation accelerated, SOD and POD activities decreased, and the plant biomass as well as the root length and root surface area decreased significantly. It was suggested that the continuous cropping obstacle of F. thunbergii was possibly caused by the nutrient deficiency, acidification, alteration of microbial flora, and oxidative stress in rhizosphere soil.

Key words: Timberline, Vegetation climate relationship, Species diversity, Temperate zone, Xiaowutai Mountains