Effects By Phragmites Australis And Iris Pseudacorus On The Characters Of The Riparian Invasive Plant:Alternanthera Philoxeroides

Invasive of alien species is an important component of global environmental change. Alien species have strong negative impacts on ecosystems and cause enormous economic losses. Increasing number of vegetation have become invasive species with land use type transferred, climate changes, and increasing emission of nitrogen and carbon. Alternanthera philoxeroides is one of the most serious invasive species in China. A. philoxeroides is able to invade water body, causing eutrophication of the environment. Its success invading always leads degeneration of ecological diversity and disturbing ecological balance. In addition, heavy growth of alligator weed always causes mosquito breeding and pathophoresis. A. philoxeroides, which growing in the riparian zone is the typical form. It is amenable to heavy distribute in water environment after invading from terrestrial environment, which seriously affecting water ecological environment and damaging the life of people.This study is divided into pot and field experiment. We investigate the impacts on A. philoxeroides by Phragmites australis and Iris pseudacorus L.. We sets six treatments:only A. philoxeroides, A. philoxeroides with P. australis, A. philoxeroides with Iris pseudacorus L., A. philoxeroides with Iris pseudacorus L. and P. australis (three different growing method)(see Fig.3-2). In each box, there are six alligator weed and twelve other plants (twelve P. australis, twelve Iris pseudacorus L. or six P. australis and six Iris pseudacorus L.). In the every block, plants were grown in similar relative positions. Every treatment has three replicates. In field experiment, five plots are selected in the riparian zone of Yingtao River., P. australis is planted besides the river in three plots. In the other two plots, we remain the previous condition. The square of every plot is1X6m2.In pot experiment, the distribution of A. philoxeroides was significantly (P<0.05) affected by P. australis and the change between land and water. At later growth stage, P. australis show greater effects on the spatial distribution of A. philoxeroides than at the initial stage. At the later stage, lateral and longitudinal diffusion distance were significantly (P<0.05) decreased by63%and44%, respectively. But it didn’t show significant effects on plant height. In addition, P. australis also showed significant (P <0.05) effects on stem length, but Iris pseudacorus L. didn’t show significant effects.In field experiment, when planting P. australis besides the river, stem mass fragment (SMF) of A. philoxeroides increased in the patch of30cm distance from the river. While in the patches of60cm and90cm, it decreased. It revealed that shading facilitated the increase of SMF for getting more light in the patch of30cm distance from the river. And root mass fragment (RMF) of A. philoxeroides decreased. The reason of it may be related to the rich water resource and high nutrient level in the riparian zone. It complied with the "functional balance". Under the non-controlled condition, the coverage of A. philoxeroides was94%, while it was76.67%in the control treatment.In conclusion, P. australis showed significant effects on the distribution of A. philoxeroides in specific space and time, while Iris pseudacorus L. didn’t show the effects. This research provided the important theoretical foundation of biological control of A. philoxeroides.