Effects Of Alternanthera Philoxeroides Invasion On Phragmites Australis Communities In Nansi Lake Wetland

Biological invasion is one of the global environmental problems and has a profound impact on the natural ecosystem.Soil seed bank represents the natural recovery potential of plant community.There have been more research results on how the invasion of exotic species affects the above-ground community than the soil seed bank,whilst it is not consistent with the performance of its aboveground community.In this research,reed communities invaded by Alternanthera philoxeroides in a short term(less than 3 years)were studied in order to better understand how biological invasion affect the local natural vegetation recovery potential.The soil seed banks of these reed communities were germinated under three light conditions(shading,natural light,and supplementary light)and three water level(dipping 30 cm,3 cm,0 cm),the affects of A.philoxeroides invasion degree,light,water level and their interactions on reed community characteristics of soil seed germination(seed density,species richness and biodiversity)were analyzed,and the above-ground community characteristics were investigated,then the effects of A.philoxeroides invasion on the species composition and the biodiversity index were analyzed.Finally,the soil characteristics(including bulk density,moisture content,p H,cation exchange amount,organic matter,available phosphorus and available nitrogen)of reed community with different invasion degrees were determined.Combined with the results of the three works,the influence mechanism of the invasion of A.philoxeroides on reed community was discussed,and the main conclusions were drawn as follows.1.The number of germination seedlings and species diversity in the soil seed bank of the reed community were significantly reduced by the invasion of A.philoxeroides Light,water invasion and the invasion degree of A.philoxeroides have interaction affects,under 0cm flooding environment,the invasion significantly reduced the potential of natural recovery of reed community by affecting their soil seed banks,under the supplementary light treatment the negative impact was more prominent,which might be due to the A.philoxeroides invasion reduced the seed density of some terrestrial species and some photogenic species in the soil seed bank of reed community.2.The Shannon-wiener diversity index and the evenness index of reed community showed a downward trend with the increasing of coverage of A.philoxeroides,which suggesting the invasion of A.philoxeroides reduces the species diversity of reed community.3.The contents of available phosphorus and available nitrogen in the soil of reed community increased significantly with the invasion of the A.philoxeroides.Soil available phosphorus content,soil available nitrogen content and soil organic matter content were significantly positively correlated.4.Based on the above three results,it can be found that the A.philoxeroides may invade the reed community by improve the effective utilization of the in the soil nutrition to promote its growth advantage when competing with the native species.In the reed communities,the increase of the A.philoxeroides coverage led to the significant loss of biodiversity and the natural recovery potential,especially the natural recovery potential of the terrestrial species and phototropic species.The resource plundering to light and the alteration to soil environment brought by the invasion may be part of the invasion mechanisms of A.philoxeroides.According to these results,some suggestions on the protection and restoration of reed community,also on the prevention and control measures of the invasion of A.philoxeroides in Nansi Lake wetland.