Reproduction determines the fitness and is a crucial component of life history. Asexual and sexual reproduction synergistically contribute to the fitness of clonal plants. Extreme warming leads to a periodical sharp rise in temperature and may affect the plant fitness. Few studies have concerned the impacts of extreme warming on the reproductive pattern of clonal aquatic plant and its evolutionary implication. In the present study, the cosmopolitan clonal submerged plant species, Potamogeton crispus L. from four different geographic sources, was subjected to simulated extreme warming. Both asexual and sexual reproductive performances including the recruitment of turions and fruits were evaluated. We found that both geographic source and warming significantly affected the reproductive performances. Although the response of turion number to warming was different for populations from different geographic sources, the turion mass did not decrease under warming. Moreover, warming induced a lower percentage of oligophyllous turions -- the turion with no more than four scale leaves each, and a higher percentage of pleiophyllous turions -- the turion with more than four scale leaves each. Additionally, warming caused a complete loss of sex for three populations. As the scale leaf functions as storage and photosynthetic organ and the scale leaf number is positively correlated with the axillary bud number, P. crispus may select to enhance the sprouting potential of turion to achieve the fitness optimization by enhancing the recruitment of scale leaves and thus larger turions under warming.

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.