Effects Of Alternanthera Philoxeroides On Soil Organic Carbon And Microorganisms,and The Responses To Nutrient And Planting Density

Biological invasion poses a serious threat to the global ecological environment,social economy and human health,therefore,it has become a hot topic in ecological research.Alternanthera philoxeroides is a worldwide malignant invasive plant,and it is one of the first invasive plants announced by China's Ministry of Environmental Protection.Nansi Lake is the largest lake wetlands in the North China Plain and it is also one of the most seriously invaded lake by A.philoxeroides.In order to understand the irnvasive mechanism of A,philoxeroides in field and provide scientific basis for the control of A.philoxeroides,this study explored its impact on soil organic carbon and microbial community diversity based on the investigation of the distribution of A.philoxeroides in Nansi Lake.The effects of different nutrients and densities on the growth of A.philoxeroides were investigated by greenhouse control experiments.Based on the results of the field investigation on the distribution of A.philoxeroides in 7 main rivers of Nansi Lake,compared with the survey data of our group for three consecutive years,the invasion trend of A.philoxeroides in Nansi Lake was analyzed.We selected 5 rivers with varying degrees of invasion,analyzed the content of organic carbon and compared the results with that of earlier periods to study the effect of increased coverage of A.philoxeroides on soil organic carboncontent.We collected soil samples in both invasion and non-invasion sites from Xinxue River,Xinxue Constructed Wetland and Shizi River,to determine the content of soil organic carbon and the diversity of soil microbial communities,investigate the relationship between soil organic carbon content and the diversity and compositions of soil microlbial community.The results of field investigation showed that the relative coverage of A:philoxeroides in 2018 increased significantly in all 7 rivers.The fluctuation of water level in Nansi Lake is probably an important environmental factor affecting its distribution.Meanwhile,with the increase of average coverage of A.philoxeroides,the content of oranic carbon increased.And we found that the invasion of A.philoxeroides significantly increased the content of soil organic carbon and there was a significant relationship between the invasive habitat and the organic carbon content.The content of organic carbon in constructed wetland was obviously higher than that in riverine wetland.The study of the relationship between A.philoxeroides and the diversity and structural composition of soil microbial communities showed that the invasion of A.philoxeroides had different effects on microbial community diversity in different types of wetland,it can affect the formation of soil organic carbon by changing the structure and richness of soil microfora.In general.the invasion of A.philoxeroides increased the diversity of soil microbial communities,which was more obvious in riverine wetland.In terms of the composition of microbial communities,different invasion levels and different habitats had different impacts.The relative abundance of the Proteobacteria and Chloroflexi at invasion sites were higher than those at the non-invasion sites,while the relative abundance of Actinobacteria was lower than that at the non-invasion sites.The results showed that A.philoxeroides and the types of wetland could affect soil organic carbon by changing the structure and richness of microbial community according to the carbon sequestration of Chloroflexi and the mineralization of Actinobacteria.By analyzing the relationship between soil organic carbon content and microbial community in different invasive habitats,it was found that the effect of soil microbial community on soil organic carbon is affected by environmental factors.There was a significant positive correlation between organic carbon content and microbial community diversity in riverine wetland.The correlation between the soil organic carbon content and microorganism that rank top 10 in relative abundance which have different significant relationship with environmental factors is different in different wetland types.That indicated the effect of microorganisms on soil organic carbon influenced by environmental factors.The results of experiments in greenhouse showed that the condition of medium plant density could improve the photosynthetic characteristics of A.philoxeroides in the same nutrient level.Under the same nutrient level,although the increase of plant density of A.philoxeroides resulted in the decrease of some physiological indexes,the whole biomass of A.philoxeroides showed an increasing trend.These characteristics may increase the population density and the competitive advantage of A.philoxeroides which were beneficial for A.philoxeroides to develop into the monodominant community.In summary,combining field observation with greenhouse control experiments,it was found that the distribution of A.philoxeroides showed an increasing trend which could be affected by the water level,and the content of soil organic carbon increased with the increase of A.philoxeroides' coverage.In addition,A.philoxeroides can affect soil organic carbon content by changing the structure and richness of soil microorganisms,and this process is affected by environmental factors.Soil nutrient level and plant density of A.philoxeroides had different effects on its growth and diffusion.At medium density,the growth status of A.philoxeroides was the best,and medium density was also conducive to the population diffusion of A.philoxeroides.This study is of great significance in understanding the interaction between environment and A.philoxeroides or other similar invasive plants.