Comparison of root traits among two invasive and three native species.
High competitiveness is vital for successful invasion by invasive plants. Previous studies related to invasive species competitiveness have primarily focused on aboveground properties, with research on root traits, which are responsible for water and nutrient uptake, remaining limited. To reveal the responses of height, biomass, and fine root traits to mixed planting (competition), we investigated two invasive species (Chromolaena odoratum (L.) R.M. King & H. Rob and Eupatorium adenophorum Speng) and three native species (Eupatorium heterophyllum DC., Eupatorium fortune Turcz., and Eupatorium japonicum Thunb.) with similar life forms from Asteraceae. Monocultures were applied as controls. Results showed that under monoculture, the two invasive species had higher values for height and shoot biomass than the three native species. However, no significant differences were found in height and aboveground biomass for the two invasive species between monoculture and mixed planting treatments. Compared with the monoculture treatments, height, aboveground biomass, fine root biomass, length, surface area, and volume were significantly reduced in the three native species under mixed planting. Furthermore, root tissue density in the two invasive species was significantly reduced under mixed planting; in addition, specific root length and specific root area were significantly increased in E. adenophorum Speng. Across the five species under monoculture and mixed planting treatments, plant height was significantly positively correlated with fine root length and root biomass, and shoot biomass was significantly positively correlated with fine root volume and surface area. Principle component analysis showed that the two invasive plants were located at the end with greater plant height and shoot biomass. In summary, the above results suggest that the two invasive plants, C. odoratum and E. adenophorum, showed strong competitiveness against the native species by modifying their carbon investment strategies in roots, especially at the seedling stage.