Highly biodiversity communities have been shown to better resist plant invasions through complementarity effects. Species richness (SR) is a widely used biodiversity metric but lacks explanatory power when there are only a few species. Communities with low SR can have a wide variety of phylogenetic diversities (PD), which might allow for a better prediction of invasibility. We assessed the effect of diversity reduction of a wetland community assemblage typical of the Beijing area on biotic resistance to invasion of the exotic weed Alternanthera philoxeroides and compared the reduction in SR and PD in predicting community invasibility. The eight studied resident species performed similarly when grown alone and when grown in eight‐species communities together with the invasive A. philoxeroides. Variation partitioning showed that PD contributed more to variation in both A. philoxeroides traits and community indicators than SR. All A. philoxeroides traits and community indicators, except for evenness index, showed a linear relationship with PD. However, only stem length of A. philoxeroides differed between the one‐ and two‐species treatments, and the diversity index of the communities differed between the one‐ and two‐species treatments and between the one‐ and four‐species treatments. Our results showed that in natural or semi‐natural wetlands with relatively low SR, PD may be a better predictor of invasibility than SR. When designing management strategies for mitigating A. philoxeroides invasion, deliberately raising PD is expected to be more efficient than simply increasing species number.

To successfully restore deteriorated lake ecosystems, it is vital to identify influencing environmental factors that impact submerged macrophytes. Planting density and water regime are important factors for submerged macrophytes' growth. While many experimental studies have examined effects of water regime on the growth of some aquatic plant species, very few have tested both planting density and water regime on population, individual, and internode growth of a submerged population. We constructed Ceratophyllum demersum populations at two density levels (four and 16 shoot fragments per pot, responding to 96 and 384 plants m ¡2), subjected to two static water depths (30 and 150 cm) and to low, medium, and high water level fluctuation frequencies (24, 12, and 6 days per fluctuation cycle of water depth change between 30 and 150 cm). Initial density had no significant effect on individuals of C. demersum; however, it had a positive effect on population performance. Fluctuation frequency did not affect the growth of C. demersum, whereas increasing water depth significantly decreased both individual and internode biomass, and also increased shoot length regardless of comparison level. We therefore conclude that managing water depth and establishing populations with higher plant density may be helpful for the restoration of submerged macrophytes in degraded wetlands.

Invasive aquatic plants have the potential to threaten ecosystem stability and biodiversity in non-native ranges; it is therefore necessary to prevent and control such invasions. While environmental heterogeneity might drive functional trait variation in plant species across different spatial scales, the drivers of trait variation over a large spatial scale are not well understood for aquatic invasive plants. Understanding functional trait variation across space and potential environmental drivers might improve our understanding of habitable conditions for predicting where an invasive plant species might be found. Here, we studied Hydrocotyle vulgaris (Araliaceae) in Zhejiang Province, China, and propose that environmental spatial heterogeneity might drive functional trait variation of this invasive aquatic plant over a large scale. The investigation was conducted across 99 plots at 7 sites with H. vulgaris. We found significant variation in functional traits over a large scale, and these functional traits were significantly different across a variety of environmental conditions. Specifically, there were significant relationships between environmental factors (i.e. temperature, precipitation, solar radiation, and water vapor pressure) and functional traits, including specific leaf area, interval length, and specific interval length, indicating that spatial environmental heterogeneity might drive the variation in functional traits (especially leaf and clonal traits) of H. vulgaris, over a large spatial scale. Our study thus provides new insights into understanding the invasiveness of H. vulgaris.

Wetlands have been demonstrated to be susceptible to invasions. Nutrient availability of wetland sediment is strongly affected by both sediment type and nitrogen deposition. We performed a greenhouse experiment to investigate the main effects and interactions between the presence of Alternanthera philoxeroides, sediment type and nitrogen deposition on biomass and evenness of experimental wetland plant communities. We established two types of plant communities, specifically wetland plant communities without and with A. philoxeroides, in two different sediment types crossed with two nitrogen deposition treatments. Experimental wetland plant communities consisted of four native or naturalised wetland species. Sediment type and nitrogen deposition significantly promoted A. philoxeroides growth. At the community level, the presence of A. philoxeroides decreased the total biomass of wetland plant species and increased community evenness, whereas sediment type significantly decreased evenness. At the species level, the presence of A. philoxeroides significantly decreased total biomass of Iris wilsonii and increased total biomass of Pontederia cordata. However, the interaction between invasion and nitrogen deposition significantly increased total biomass of Butomus umbellatus. These findings suggest that both sediment type and nitrogen deposition promote A. philoxeroides growth and exacerbate A. philoxeroides invasion into wetland plant communities. However, the presence of A. philoxeroides can increase the evenness of the wetland plant communities at a small scale by suppressing dominant species. The findings of the present study provide insights into the management of A. philoxeroides in wetlands.

Aims Native plant communities are commonly invaded by invasive plants to different degrees. However, the relative contribution of the invasive plant abundance vs. phylogenetic evenness to the responses of wetland communities to different degrees of invasion is still unclear. In addition, whether such contribution varies with environmental conditions such as flooding is also unclear. Methods To address these questions, we chose Alternanthera philoxeroides as the invasive plant, and set up four invasive degrees by changing the community species composition under both flooding and non-flooding conditions. The relative abundance of A. philoxeroides and phylogenetic evenness changed simultaneously with the change in the community invasion degree. Important Findings The invasion degree significantly affected the individual biomass of A. philoxeroides and some native species. Variation partitioning showed that the relative abundance of A. philoxeroides contributed more to variation in community indicators than phylogenetic evenness, regardless of flooding. Spearman rank correlation test showed that the relative abundance of A. philoxeroides was negatively correlated with the individual biomass of A. philoxeroides and some native species, while the phylogenetic evenness was positively correlated with only a few native species. And their correlation strength and significance were all affected by specific species and flooded environment. In conclusion, our results suggest that the relative abundance of A. philoxeroides can more effectively explain the wetland community response to different invasion degrees than phylogenetic evenness, regardless of flooding.