Abstract: Vegetation communities of the Yangtze river-lake floodplain zone subject to water-level fluctuation have been observed to gradually evolve into a mono-specific stand of Carex thunbergii. This study aimed to determine if there is evidence for allelopathy as one of the mechanisms mediating the observed plant community transition. We studied the effects of C. thunbergii extracts on seed germination, seedling growth and antioxidant activity of three accompanying Poaceae species (Lolium perenne, Cynodon dactylon, Phalaris arundinacea). It was found that the extracts of C. thunbergii significantly inhibited the germination rate, germination potential, radicle length and germ length of the three tested grass species. Inhibition of seed germination rate was >95% at the highest extract concentration, for all three tested grasses. At the same concentration, a methanol extract of C. thunbergii had more inhibitory effect than an aqueous extract. The seedling growth was significantly affected by C. thunbergii extracts, and the root:leaf ratio was significantly lower than for control seedlings. Levels of malondialdehyde in L. perenne and P. arundinacea increased with the concentration of extract. The activities of superoxide dismutase and peroxidase in L. perenne initially rose, then fell, increasing concentration of C. thunbergii extract. Our results show that C. thunbergii has potential for allelopathic inhibition of seed germination of the three tested grasses and inhibition of seedling growth of L. perenne and P. arundinacea. Our findings indicate that allelopathy may play a role in the dominance of C. thunbergii in Shengjin Lake.

Key words: Carex thunbergii, water-level fluctuation zone, allelopathy, wetland, dominant species