The Effects And Mechanism Of Noxious Weed Ligularia Virgaurea Removal On Soil Microbial Community In Qinghai-Tibet Plateau

Ligularia virgaurea is the dominant noxious weed in Qinghai-Tibet Plateau,which has an important impact on local biodiversity and ecosystem function.In recent years,the expansion trend of L.virgaurea has become more obvious,which poses a serious threat to animal husbandry and social development in Qinghai-Tibet Plateau.Many studies have explored the ecological mechanism and effects of the expansion about L.virgaurea from different perspectives.It was found that the expansion of L.virgaurea could affect the growth of adjacent plants,affect the soil physiochemical properties,and change the structure and diversity of soil microbial community.Due to the fact that most of these studies currently use the method of field investigation,it is difficult to distinguish the effects of L.virgaurea from those of other ecological factors,and unable to accurately reveal the impact mechanism of L.virgaurea.In addition,most of the current studies on the impact of L.virgaurea on soil microbial community only focus on the degree and scope of its impact,while there are few studies on the effect mechanism of L.virgaurea on soil microbial community.Among them,the research on the direct and indirect effects of L.virgaurea on soil microbial community have not been reported.Therefore,in this study,L.virgaurea,the dominant noxious weed in the alpine meadow of the Qinghai-Tibet Plateau was selected as the research object,the experimental treatment was set to remove the L.virgaurea.Through determination of soil physiochemical properties,quadrat analysis of aboveground plant community,high-throughput sequencing and statistical models,to explore the influence of L.virgaurea removal on soil microbial communitiy and their direct and indirect regulatory mechanism.The main conclusions of our study are as follows:1)L.virgaurea significantly reduced soil nitrate content by 37.8%,but had no significant effect on other soil physiochemical properties.L.virgaurea had no significant effect on the richness,shannon diversity and biomass of plant community,but significantly altered the species composition of plant community,and had no significant effect on the biomass of grasses and legumes,but significantly increased the biomass of forbs by 47.1%.2)L.virgaurea had no significant effect on the soil bacterial community richness and shannon diversity and fungal community shannon diversity,but significantly reduced the fungal community richness by 20.0%.The results of nonparametric multivariate analysis of variance showed that L.virgaurea had no significant effect on soil bacterial and fungal communities composition.The results of indicspecies analysis showed that the indicspecies of the soil bacterial community mainly belonged to Proteobacteria,Actinomycetes and Planctomycetes,and the indicspecies of the fungal community mainly belonged to Basidiomycota in the presence of L.virgaurea.While the indicspecies mainly belonged to Chloroflexi,Patescibacteria,Proteobacteria,Bacteroidetes,Gemmatimonadetes and Firmicutes,and the indicspecies of fungal community mainly belonged to Ascomycota,Basidiomycota,Chytridiomycota and Glomeromycota after the removal of L.virgaurea.3)There was a significant correlation between soil bacterial richness,shannon diversity and soil fungal richness,shannon diversity.Soil nitrate content was significantly correlated with bacterial and fungal richness,shannon diversity.Soil p H value was significantly correlated with shannon diversity of bacterial community.Other soil physiochemical factors and plant community richness,shannon diversity were not significantly correlated with bacterial and fungal richness,shannon diversity.The results of redundancy analysis showed that the main soil physiochemical factors affecting the bacterial community composition were soil nitrate and ammonium,while the main soil physiochemical factor affecting the fungal community composition was soil nitrate.The results of Mantel test showed that there was a significant correlation between soil bacterial community composition and soil fungal community composition,and soil bacterial community composition had no significant correlation with plant community composition,while soil fungal community composition had a significant correlation with plant community composition.4)The results of structural equation model showed that L.virgaurea had no significant direct effect on the richness,shannon diversity of soil bacterial and fungal community.L.virgaurea indirectly reduced the richness,shannon diversity of soil bacterial and fungal community by reducing soil nitrate content.Although L.virgaurea had a significant direct effect on the composition of plant community,the indirect effects on soil bacterial and fungal communities composition through the composition of plant community were not significant.Our results illustrated the influence and regulation mechanism of L.virgaurea on soil microbial community,clarified the direct effects of L.virgaurea on soil microbial community and their indirect effects through soil physiochemical properties and plant community,revealed the important role of soil nitrate in the regulation of soil microbial community by L.virgaurea.This study provided theoretical guidance for us to further understand the expansion mechanism of L.virgaurea and its effects on biodiversity and ecosystem function in Qinghai-Tibet Plateau.