Few studies have evaluated the relative importance of various factors in the invasion process of exotic plants in freshwater ecosystems due to the difficulty of observing numerous factors simultaneously. In this study, to explore how various biotic and abiotic factors determine the overall invasion extent of all exotic plants and the invasion extent of different life-form exotic plants as well as assess their relative importance, we surveyed 236 exotic aquatic plant communities using 2267 fine quadrats in China's freshwater ecosystems. We found that competition from native plants was the most vital factor determining the mean biomass of all exotic plants and biomass of submerged plant Cabomba caroliniana, while competition from co-occurring exotics was the most important for biomass of emergent plant Alternanthera philoxeroides and free-floating plant Eichhornia crassipes. The population biomass of different exotic species responded differently to climate change. Water eutrophication could accelerate the invasion of exotic plants by directly favoring them and indirectly weakening the resistance of native plants. Water depth, habitat size, herbivory, and anthropogenic disturbance had relatively weak impacts on the biomass of exotic plants. Moreover, some factors have different modes of influence on different exotic plants. Our study suggested interspecific competition plays a more important role in the population spread of exotic plants than climate and abiotic environment once the plants have successfully established, implying that biodiversity conservation and vegetation restoration were the fundamental methods to control invasion. In addition, our study highlights the importance of studying the overall invasion extent of all exotic plants and interactions among invaders in multi-invader communities.

The relationship between producers (e.g., macrophyte, phytoplankton and epiphytic algae) and snails plays an important role in maintaining the function and stability of the shallow ecosystems. A complex relationship exists among macrophytes, epiphytic algae, phytoplankton and snails. An outdoor mesocosm experiment with two-way factorials was carried out, three species submerged macrophytes (Hydrilla verticillate, Vallisneria natans or one exotic submerged plant Elodea nuttallii) and two grazing treatments (4 snail species present or absent) to elucidate those relationships. The results showed that the snail communities reducing the biomass of phytoplankton and epiphytic algae indirect then enhanced the growth of the submerged macrophytes. The macrophyte with complex architecture supported more snail and epiphytic algae, and snails preferred to feed on native plants. Competition drove snails change the grazing preferences to achieve coexistence, so that led to the assembling of snail communities towards the direction of highest resource utilization.