Abstract: Common ragweed (Ambrosia artemisiifolia) seeds were collected from Mentougou District, Beijing, China, and a field experiment was conducted in a fallow field in Shunyi District, Beijing, China, during 2013-2014. In order to evaluate the effect of propagule pressure on common ragweed’s recruitment, colonization and population persistence, four levels of common ragweed seeds (5, 10, 20 and 40 seeds·m^-2) were sown in 12 plots. The results showed that there was a positive correlation between propagule pressure and the proportion of plots with common ragweed successfully recruited and colonized in both 2013 and 2014. When the propagule pressure reached or were more than 20 seeds·m^-2, the population of common ragweed could be successfully established and even continued to expand next year. The number of common ragweed recruited and colonized in the plots in the second year was significantly higher than in the first year (P<0.05). The plots that had 1-3 seedlings successfully colonized in 2013 were able to maintain their population in 2014, in which the number of seedlings recruited in 2014 ranged from 5 to 237, and only 4 to 97 adult plants were successfully colonized at the end of the experiment. Results indicate that low propagule pressure of common ragweed can likely cause invasion, and the probability of successful colonization increased with propagule pressure; only a few plants of common ragweed may produce enough seeds for population persistence and expansion. As a result, it is necessary to strengthen the quarantine of common ragweed seeds and eliminate the few plants occurred in new distribution area in time.

Key words: soybean, grain filling stage, drought stress, photosynthetic capacity, root growth.