Functional traits under treatments
The results of this study confirmed the hypothesis that flooding along with additional nitrogen promote the growth of invasive plant species because of higher phenotypic plasticity and better competition intensity. It also indicates that functional traits play an important role for the success of invasive plant species under nitrogen enrichment and flooded habitats. The results showed that WT was particularly taller than WC regardless of the water, nitrogen and plant culture methods (monoculture and mixed culture). WT may be more competitive in resource acquisition due to its tallness, particularly for water and nitrogen, which maybe the most dominant ecological factors that affected plant growth and survival (Drenovsky et al., 2012, Liu et al., 2018a). In addition, SLA of WT was larger than WC, supposedly due to larger leaf area and traits response under resource-rich habitats (Matzek, 2012), but some studies pointed out higher growth rate; due to more biomass of leaf rather than leaf structure per unit area (Gallagher et al., 2015, Huang et al., 2016). However, SLA of WC was significantly lower than WT in the treatment under both the cultures, except only CK (Fig. 2d). Hence, SLA may play a role in successful invasion of WT. While many plant species enhance their growth rate by increasing leaf area, SLA and leaf transpiration rate (LeBel et al., 2013). In this study, higher plant height of WTserves as a strategy to enhance competition for light; however, this imposes a cost in the form of structural support and water transport (Wang et al., 2017). Therefore, plant species can have higher relative growth rate by increasing plant height and decreasing SLA (Fig. 2a, 2d and Fig. 5), especially in high nitrogen and flooding conditions (F.N and F.2N) (Drenovsky et al., 2012).