Biological invasions of aquatic plants (i.e., macrophytes) are a worldwide phenomenon, and within the last 15 years researchers have started to focus on the influence of these species on aquatic communities and ecosystem dynamics. We reviewed current literature to identify how invasive macrophyte species impact fishes and macroinvertebrates, explore how these mechanisms deviate (or not) from the accepted model of plant-fish interactions, and assess how traits that enable macrophytes to invade are linked to effects on fish and macroinvertebrate communities. We found that in certain instances, invasive macrophytes increased habitat complexity, hypoxia, allelopathic chemicals, facilitation of other exotic species, and inferior food quality leading to a decrease in abundance of native fish and macroinvertebrate species. However, mechanisms underlying invasive macrophyte impacts on fish and macroinvertebrate communities (i.e., biomass production, photosynthesis, decomposition, and substrate stabilization) were not fundamentally different than those of native macrophytes. We identified three invasive traits largely responsible for negative effects on fish and macroinvertebrate communities: increased growth rate, allelopathic chemical production, and phenotypic plasticity allowing for greater adaptation to environmental conditions than native species. We suggest that information on invasive macrophytes (including invasive traits) along with environmental data could be used to create models to better predict impacts of macrophyte invasion. However, effects of invasive macrophytes on trophic dynamics are less well-known and more research is essential to define system level processes.

Changes in the world's species composition and the loss of biodiversity have prompted a closer investigation of the importance of biodiversity and community composition to ecosystem functioning. However, few studies have explored this relationship outside of controlled experiments. Here, we examined the relationship between plant diversity, primary production, and methane efflux in freshwater wetlands in an across-site field study and assessed the applicability of experimental findings to natural wetlands. Four wetland sites in central Ohio (USA) were divided into two plant communities, one dominated by clonal species and one dominated by non-clonal species. We found that plant diversity was negatively correlated with aboveground biomass in both the clonal and non-clonal communities. Overall, plant community composition was a stronger predictor than diversity of the response variables and in certain instances a stronger predictor than environmental factors such as soil organic matter content, moisture content, and pH. Thus, plant community composition is an important driver of ecosystem functioning in depressional wetlands beyond the well-known environmental factors. Additionally, our work indicates that results from experimental wetland studies of the relationship among diversity, biomass and methane emission are not applicable to the wetland ecosystems included in our study.

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