High phosphorus availability and low light intensity resist the invasiveness of alien plant Chromolaena odorata on tropical coral islands

Abstract The vegetation and ecosystems of the Paracel Islands are extremely fragile and very difficult to restore after destruction. Chromolaena odorata is one of the most common invasive plants as guano phosphorus input constantly decreasing for islands, which has caused substantial harm to native vegetation on the Paracel Islands in recent years. In the current study, we investigated the growth and interspecific competition of C. odorata with the native species Pisonia grandis and Scaevola taccada as affected by light intensity and soil P content. The experiment, which was conducted in greenhouse, had two light intensities (full light or 10% light) and three levels of soil available phosphorus (P) content (53.89 mg·kg-1 low P, 253.89 mg·kg-1 medium P, and 1053.89 mg·kg-1 high P). The results showed that low light intensity significantly inhibited the growth of P. grandis, S. taccada, and C. odorata. However, compared with the low P treatment, 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 between C. odorata, P. grandis, and S. taccada was affected by light intensity and plant species. Compared with the low and medium P treatments, the high P treatment significantly reduced the competitive advantage of C. odorata over P. grandis. The results demonstrate that shaded habitats with high soil P content could restrict invasion by C. odorata. This suggests that the invasion on tropical coral islands by C. odorata can be reduced by protecting the native vegetation (to increase shade) and seabirds (to increase soil P content).