High phosphorus availability and low light intensity reduce the competitive ability of the invasive plant Chromolaena odorata in tropical coral islands

Chromolaena odorata is one of the most common invasive plants, as the phosphorus input from guano in the coral islands continuously decreasing, causing substantial harm to the native vegetation in recent years. In the current study, we investigated the effects of soil phosphorous content, light intensity and competition on several physiological traits (plant height, leaf area, maximum net photosynthetic rate, and relative growth rate) of C. odorata and the native species Pisonia grandis and Scaevola taccada based on a greenhouse experiment with two light intensities and three levels of soil available phosphorus (P) content. We also evaluated the effects of light intensity and soil phosphorus content (and their interaction) on the relative yield and aggressivity coefficient of the invasive species C. odorata . The results showed that low light intensity significantly inhibited the growth of the three species. However, the high P treatment significantly inhibited the growth of C. odorata and P. grandis and significantly increased the growth of S. taccada under full-light conditions. The effect of soil P content on the interspecific competition among C. odorata , P. grandis , and S. taccada was mediated by light intensity and species combination. The high P treatment significantly reduced the competitive advantage of C. odorata over P. grandis . The results demonstrate that shaded habitats with a high soil P content could restrict invasion by C. odorata. This suggests that the invasiveness of C. odorata in tropical coral islands can be reduced by protecting native vegetation and thus increasing shade and soil P content.