| In recent years,the damage caused by invasive plant species on the structure and functioning of native ecosystems has become increasingly serious.Therefore,the mechanism driving the successful invasion of invasive plant species has become one of the scientific issues in the field of environmental ecology.Numerous findings presented that invasive plant species can affect the growth performance of native plant species via their greater growth competitiveness and subsequently alter the structure and functioning of native plant communities.Meanwhile,invasive plant species can also trigger an obvious shifts in the structure and functioning of microbial community in their rhizosphere soil via the plant-soil feedbacks and thereby create a soil microenvironment that is favorable to their further invasion process.Further,the rapid progress of urbanization in China recently can increasingly raise the level of heterogeneity and fragmentation of urban landscapes.However,the gradually increased level of heterogeneity and fragmentation of urban landscape can significantly alter the chance of successful invasion of invasive plant species,especially via the mediated empty niches which can facilitate the invasion degree of invasive plant species.Thus,it is crucial to make a comprehensive comparative analysis to reveal the impacts of invasive plant species on the native ecosystems under the background of landscape heterogeneity in urban to further clarify the mechanism driving the successful invasion of invasive plant species,especially under the landscape heterogeneity in urban.The results can also lay a solid theoretical support platform for ecological management as well as early warning prevention and control of invasive plant species,and then provide a strong practical theoretical basis for build a “modern and beautiful China in which harmonious co-existence between human and nature”.Based on this,this study aims to estimate the impacts of the notorious invasive plant species Solidago canadensis L.on plant taxonomic diversity,plant functional diversity,community stability,and soil nitrogen-fixing bacterial community and the driving mechanisms in nine types of urban landscapes(i.e.,cultural and educational research site,farmland wasteland;garden scenic area,industrial district,municipal land,residential area,traffic land,urban green space,and wetland waterfront).The results of the present study can further clarify the mechanism driving the successful invasion of invasive plant species typified by S.canadensis under the condition with landscape heterogeneity in urban and can build strong theoretical support for ecological management as well as early warning prevention and control of invasive plant species.The main results of the present study are as follows:1.Impacts of S.canadensis invasion on plant functional traits and plant functional diversity as well as the driving mechanism under the landscape heterogeneity in urban:(1)Some functional traits indices of S.canadensis show higher values than native plant species in certain invaded areas,especially plant height and ground diameter(P<0.05).The higher plant height can make S.canadensis obtain a greater competitive advantage in resource capture and utilization(especially the competitive advantage for sunlight)than native plant species.The higher ground diameter can make S.canadensis get a greater supporting capacity than native plant species.(2)S.canadensis and coexisting native plant species tend to functional convergence(i.e.,functional similarity).Thus,the similarity in functional traits between S.canadensis and coexisting native plant species support the habitat filtration hypothesis.(3)There are obvious differences in plant functional diversity in different types of urban ecosystems.S.canadensis invasion can significantly increase plant functional diversity in some urban ecosystems.This may be related to the obvious differences in the nine types of urban landscapes and the plant functional traits in different urban ecosystems.(4)The relative abundance of S.canadensis is positively related to plant functional diversity(i.e.,community-weighted mean trait values,Rao's quadratic entropy,and Mason ? functional diversity)(P<0.05).Hence,S.canadensis invasion can significantly affect plant functional diversity.Further,the communities with higher plant functional diversity are more vulnerable to invasion than those with lower plant functional diversity.Lastly,plant functional diversity of traffic land is higher than that of other eight types of urban landscapes and thereby community invasibility of traffic land may be greater than that of the other types of urban landscapes.2.Impacts of S.canadensis invasion on plant taxonomic diversity and community stability and the driving mechanism under the landscape heterogeneity in urban:(1)There are significant differences in plant taxonomic diversity and community stability in the nine types of urban landscapes(P<0.05).However,S.canadensis invasion did not significantly affect taxonomic diversity and community stability of native communities(P>0.05).Hence,heterogeneous landscapes,rather than S.canadensis invasion,is essential for the shifts in plant taxonomic diversity and community stability.(2)There is a close positive correlation between plant taxonomic diversity(especially diversity and evenness)and community stability both in non-invaded and invaded areas in the nine types of urban landscapes(P<0.001).Therefore,the results support the diversity hypothesis.(3)There are no significant correlation between the relative abundance of S.canadensis and community stability(P>0.05).Accordingly,the relative abundance of S.canadensis did not act a key role in the alterations of community stability.The main reason may be attributed to the fact that S.canadensis invasion did not significantly affect plant taxonomic diversity and community stability.(4)There is a significant negative correlation between the relative abundance of the most dominant species and community stability,and the affinity of the negative correlation has been reduced under the condition with S.canadensis invasion mainly due to the limited effective resources(P<0.001).3.Impacts of S.canadensis invasion on soil nitrogen-fixing bacterial community and the driving mechanism under the landscape heterogeneity in urban:(1)There are significantly differences in the diversity and abundance of soil nitrogen-fixing bacteria in the nine types of urban landscapes(P<0.05).However,S.canadensis invasion did not obviously affect soil physical-chemical properties(P>0.05),and the diversity and richness of soil nitrogen-fixing bacteria.But S.canadensis invasion significantly affects soil nitrogen-fixing bacterial community and ? diversity,especially there are obvious changes in the relative abundance of certain soil nitrogen-fixing bacteria groups.Specifically,some taxonomic groups of nitrogen-fixing bacteria(i.e.,f_Micromonosporaceae,f_Oscillatoriaceae,and f_Bacillaceae)may be crucial for the process of S.canadensis invasion.Consequently,S.canadensis invasion may facilitate the successful invasion by affect soil nitrogen-fixing bacterial community and ? diversity,rather than ? diversity or the relative abundance of soil nitrogen-fixing bacteria.This may be related to the created allelopathy recruited by the released chemical substances(i.e.,allelopathicals)which can affect the resource capture and utilization level of soil nitrogen-fixing bacteria.(2)The abundance of nifH gene in farmland wasteland is higher than that of other eight types of urban ecosystems.Meanwhile,there is a positive correlation between nifH gene abundance and nitrogen fixation rate.Accordingly,the higher diversity and richness of nitrogen-fixing bacteria in farmland wasteland can significantly increase the level of available nitrogen in the soil subsystems,which may enhance the further invasion process of S.canadensis.(3)Electrical conductivity may be the main soil physical-chemical factor that drives the changes in soil nitrogen-fixing bacterial community(based on ? diversity analysis).This may be due to the significant differences in soil electrical conductivity among the nine types of urban ecosystems,which in turn may cause significant changes in the carbon source utilization patterns of soil nitrogen-fixing bacteria.(4)The relative abundance of S.canadensis may be the most important environmental variable of plant community that drives the changes in soil nitrogen-fixing bacterial community(based on ? diversity analysis).Thus,soil nitrogen-fixing bacterial community may be largely affected by the invasion degree of S.canadensis. |
PDF Full Text Request