Abstract: Ipomoea cairica (Convolvulaceae), a perennial herbaceous liana, has become a major invasive weed with strong invasiveness in the east part of Guangdong Province, China. In a field investigation, five patches of land that had been heavily invaded by I. cairica were chosen as sample plots, and five adjacent patches of land free of I. cairica or other invasive plants were set as control group. Coenological survey of the plants in all the 10 plots was performed using the quadrat method for calculation of species diversity index, and soil samples were collected from the sample plots for analysis of soil enzyme activity and physico-chemical indices, so as to explore interactions between I. cairica and eco-factors of the invaded area and evaluate impacts of the invasion on ecosystem. Results show that the invasion decreased plant richness and diversity to a significant (P<0.05)or an extremely significant extent(P<0.01), and its effect of crowding out native species was especially obvious. In all the sample plots, except for the forest park plot, the invasion increased the activities of invertase, urase, phosphatase and nitrate reductase (NR), which are closely related with soil fertility, notably by 26.91% -55.52%. Besides, it increased the contents of TN, AN, TK and AK, but reduced the contents of TP, AP and OM in the soil, all to a significant (P<0.05) or an extremely significant extent (P<0.01). The findings suggest that invasive weed I. cairica can alter the structure and composition of the community and improve soil enzyme activities and soil nutrient levels, thus forming a micro-ecoenvironment that is beneficial to development and growth of the plant per se and expansion of its population.

Key words: invasive weed, Ipomoea cairica, diversity index, soil physicalo-chemical properties, interspecific competition