Responses Of The Invasive Plant Hydrocotyle Vulgaris To Environmental Variation

Wetland has many important ecological functions,but is also one of the ecosystems most severely invaded by exotic plants.Hydrocotyle vulgaris is native to Europe,Southern North America,and Central America,and was introduced into China as an ornamental plant in 1990s.H.vulgaris is widely used in wetland landscape and indoor greening.However,because of its high adaptability and rapid spread,it has generated great effects on wetland ecosystems,especially in south China,and is listed as an exotic invasive plant in China.The comparison of genotypes of invasive plants from native and invasive ranges can give insight into the mechanism underlying their successful invasion.However,it is still unclear whether H.vulgaris in invaded ranges shows differences in growth and morphology and also different growth and morphological responses to environmental variations,which are potentially able to facilitate invasion.A series of controlled experiments were conducted to compare growth and morphological responses of genotypes of H.vulgaris from native and invasive ranges to different environmental variations.The outcomes were expected to contribute to our understanding of the mechanism underlying the successful invasion of this wetland invasive plant.The results are as follows:?1?Genotypes of H.vulgaris from native and invasive ranges were grown without nitrogen addition or with nitrogen addition of three forms?NH ₄⁺-N,NO ₃^--N and Glycine-N?.The genotypes of H.vulgaris from the invasive range had significantly higher biomass and ramet number than the native genotypes.Compared with the native genotypes,the invasive genotypes increased more biomass and ramet number with nitrogen addition.Biomass allocation and morphological responses to nitrogen treatments were significantly different between the invasive and the native genotypes.?2?Genotypes of H.vulgaris from native and invasive ranges were grown with or without flooding.Regardless of flooding,the genotypes of H.vulgaris from the invasive range had significantly greater biomass accumulation and clonal growth capacity than the native genotypes.Compared with the native genotypes,the invasive genotypes showed stronger flooding tolerance by less biomass reduction.Moreover,the invasive genotypes relieved flooding stress by increasing ramet height and biomass allocation to leaves,showing the escape strategy.?3?Genotypes of H.vulgaris from native and invasive ranges were grown in three types of containers with different sizes.The genotypes of H.vulgaris from the invasive range grew more vigorously than the native genotypes.The genotypes from the invasive range also showed significant growth and morphological responses to the container types.In contrast,the native genotypes did not show a significant growth response to the container types,and in terms of morphology only specific stem length showed a significant response.?4?Clonal fragments of genotypes of H.vulgaris from native and invasive ranges were grown in a heterogeneous light environment with the apical ramet grown in 30%of ambient light,the basal exposed to 100%of ambient light,and the connection between the apical and basal ramets either severed or left intact.Regardless of severance,the genotypes from the invasive range accumulated more biomass than the native ones.Under the heterogeneous light environment,effects of clonal integration on the growth did not differ significantly between the native and the invasive genotypes.However,clonal integration affected biomass allocation of the basal ramet of the invasive genotypes,showing specialization for abundance,but had no such an effect in the native genotypes.To summarize,H.vulgaris showed adaptive changes in response to different environmental variations in the invasive range,the changes may be due either to evolution after introduction or to some genotypes have been eliminated in the early invasion,or the combination of the two factors.