The Relationship Between Distribution Of Alternanthera Philoxeroides And Environmental Factors In Main Inflowing Rivers Of Nansi Lake

Biological invasion has caught extensive concern in ecology for its enormous harm and potential risk, and these harm may be further accelerated by human activities and global changes. Alligator weed (Alternanthera philoxeroides (Mart.) Griseb.) is a worldwide malignant invasive species, and is also one of the sixteen invasive species that caused severely damage in China. Nansi Lake, the biggest freshwater lake in North China, which is severely invaded by A. philoxeroides, provides favorable condition to this study. The study of distribution of A. philoxeroides in Nansi Lake and its influencing factors will not only provides scientific basis to control its invasion, but also has important significance to reveal environmental factors of plant invasion.In order to investigate the environmental factors influencing the distribution of A. philoxeroides, a three-year investigation was conducted of seven main rivers of Nansi Lake. Meanwhile, in order to find out more about the effects of invasion on soil properties and soil microbial community structure, and effects of different degrees of invasion and different wetland types on soil microbial community on a microscopic view,8 sites have been selected, where were separately distributed in Xinxue River, Xinxue River Constructed Wetland and Shizi River, including invaded and non-invaded sites by A. philoxeroides; sampling soil and the root of A. philoxeroides to analysis the similarity/difference of microbial community structure between root and soil and inherent connections between root endophytes and soil microbes.The same environmental factors will have different impacts at different scales. As field investigation results showed, all the seven rivers were slightly or heavily invaded by A. philoxeroides, even the same river changed much in different years. Water velocity and water level probably were vital environmental factors influencing its distribution. Rapid water velocity may hold back the invasion of A. philoxeroides as well as provide a convenient way for the invasion of A. philoxeroides. Disturbances caused by irregular water transfer may severely undermine plant diversity in riparian zone.The study of the relationship between invasive plants and soil properties showed that A. philoxeroides coverage was positively correlated with higher SOC and negatively correlated with lower soil TN and root C/N ratio. The average SOC was higher in heavily invaded rivers than lightly invaded rivers, but there was no significant difference between invaded and non-invaded plots in the same river. Soil pH was negatively correlated with A. philoxeroides coverage, SOC and soil TN. Maybe the soil properties only took effects in the big scale like river scale, not significant in the small scale. Invasive plant distribution may be positively related to SOC and soil TN of rivers. Efforts to prevent A. philoxeroides invasion should focus on rivers with higher SOC, higher soil TN and lower soil pH. Selecting proper study scale is vital to reveal biological invasion disciplines, and the selection should be according to relevant research purpose.Both the plant invasion and wetland types might have significant influence on soil microbial community. Overall, invaded sites have a significant higher community diversity than non-invaded sites, while they have the similar community richness as Chao 1 and ACE (Abundance-based Coverage Estimator) were really close to each other. Community diversity was higher in invaded sites than non-invaded sites, however, in different wetland type, the components of community diversity were very different. In non-invaded sites, the community diversity of constructed wetland was higher than river wetland, while it was opposite in invaded sites. The constructed wetland have richer Bacteroides in invaded sites, while have richer Proteobacteria in non-invaded sites. Plant invasion promoted higher nitrogen turnover rates in soils. Nitrospirae was much richer in constructed wetland than river wetland in our study, but that was not related to invasion, which means that nitrogen fixation mainly happened in soils.The community diversity and richness of endophytic bacteria were both lower than that of soils. Cyanobacteria, a dominant phylum in root, was barely found in soil; Nitrospirae, was significantly much richer in soil bacterial community than that in root. These discrepant phyla have compact connections with nitrogen utilization. Endophytic bacteria in root and soil bacteria could be separated into two cluster very easily. The difference was greater in endophytic bacteria communities of root than soil among different sampling sites.In general, integrating field investigations and lab analysis, it was found that the distribution of A. philoxeroides was largely effected by water velocity and water level, and the coverage of that was correlated to soil organic carbon, total nitrogen, and pH value. The results showed that the efforts to prevent A. philoxeroides invasion should focus on rivers with higher SOC, higher soil TN and lower soil pH. The effects of A. philoxeroides invasion on the soil properties was more significant at the big spatial scales, for example at river scale. The invaded sites have a significant higher soil microorganism community diversity than non-invaded sites, meanwhile, both the plant invasion and wetland types would have significant influence on soil microbial community. The community diversity and richness of endophytic bacteria in root were both lower than that of soils and the dominant bacteria in root was not dominated in soils. This research has important significance to understand the interaction between invasive plant and environmental factors.