Effect of UV-B Radiation on the Growth of Alien Myriophyllum aquaticum

Myriophyllum aquaticum is an invasive plant that poses a threat to native plants and industries in China. Therefore, this study aimed to specifically investigate the effects of varying UV-B radiation intensities on the growth and physiological traits of M. aquaticum. We established three treatment groups: (1) a control group exposed to natural UV-B radiation (~20.0 μW·cm−2), (2) a +25% group exposed to UV-B irradiance increased by 25% (~25.0 μW·cm−2), and (3) a +50% group exposed to UV-B irradiance increased by 50% (~30.0 μW·cm−2). In the +50% group, the growth indices decreased but were still slightly higher than those in the control group, and the plants survived and maintained normal physiology throughout the experimental period. This suggests that M. aquaticum is tolerant of UV-B radiation. However, there may be a threshold beyond which negative effects are exacerbated. As the UV-B irradiance increased, the number of meristems and tillers, as well as the flavonoid content, increased, whereas the malondialdehyde (MDA) content initially decreased and then increased. Thus, M. aquaticum may respond to increased UV-B radiation stress by up-regulating the biosynthesis of secondary metabolites, such as flavonoids. This species adapts to environments with different levels of UV-B radiation by adjusting its morphological characteristics and physiological metabolism, thereby enabling successful invasion.