Natural Succession Characteristics And Mechanism Of Plant Communities In Abandoned Metal Mines In Gejiu,Yunnan

Metal mining causes serious damage to vegetation and topographic structure,but also transports a large amount of heavy metals to the environment,reducing land use and causing serious heavy metal pollution.Therefore,it is very important for sustainable development of human beings to restore vegetation community diversity,structure and functions in abandoned mining areas.Ecological restoration methods are mainly used in abandoned mining areas,and the common measures include soil covering,seed introduction,microbial addition or a combination of multiple measures.Compared with physical and chemical restoration,the cost of ecological restoration is lower,but the restoration of large-scale abandoned land still needs a lot of money.The natural succession of vegetation is a reasonable and orderly process,and can finally reach a community with self-rehabilitation ability.Its succession rules can provide theoretical basis and scientific guidance for ecological restoration.However,at present,the domestic ecological restoration research mainly focuses on the "afforestation" model restoration,and pays little attention to the natural succession characteristics and mechanism of plant communities in abandoned mine.Therefore,this study uses chronosequence approach to study the important ecological process and mechanism of vegetation succession in abandoned metal mining areas with different abandoned times in Gejiu City,Southwest Yunnan Province.The specific research conclusions are as follows:1.Global Meta analysis shows that natural succession has a positive impact on increasing vegetation diversity,evenness and species richness.In terms of succession rate,natural succession is easier to restore vegetation diversity in temperate and moderate climate areas.The vegetation succession trend(i.e.,restoration effect)of abandoned metal mine is related to climate.Compared with tropical and mesothermal areas,the vegetation community characteristics and environmental conditions in cold areas are more difficult to successful succession.In addition,the larger the mining scale(mining area and time),the more difficult it is to increase vegetation diversity.The results show that the characteristics of mine recovery vary greatly under different site conditions.Therefore,this study took an abandoned metal mines in Gejiu as the object to explore the natural succession characteristics and mechanism.2.In Gejiu study site,the diversity,composition and function of vegetation community have changed with the occurrence of succession significantly,developing towards the local natural forest.The species richness,Shannon diversity index and evenness of vegetation community increased,and the beta diversity decreased gradually.In each stage,more species with strong metal enrichment ability,and the flowering and fruiting periods of plants larger in the early stage.In the later two stages of succession,the therophyte decreased and the proportion of phanerophyte increased.At the initial stage of succession,S strategy was the main strategy,and the succession enters the next stage,score of C strategy increased.At this time,there is niche differentiation,allowing more species to co-occur.3.The assembly mechanism of succession vegetation community changed in different stages,convergence of functional traits indicates that community assembly is mainly restricted by environment or dispersal,while divergence indicates that community construction is influenced by interspecific competition.Based on the null model comparison,the comprehensive establishment traits shifted from converged to neutral,while the comprehensive regeneration traits converged and diverged alternately.After more than 20 years of succession,the comprehensive establishment traits were consistent with the expected values,while the comprehensive regeneration traits diverged significantly.These results indicated that the strong environmental filtering and dispersal limitation determined the assembly of the community in the early stage of succession,and the influence of environmental conditions gradually decreased with the passage of time.In different succession stages,dispersal limitation and interspecific competition dominated the vegetation assembly,and were mainly influenced by stochastic processes in the late succession stage.4.The total contents of Sn and Cu in the abandoned bare land of mine were higher,similarly the available Cu and Cr were higher,which decreased with the succession.In the early stage of succession,the contents of N and P were low and gradually increased with the succession time,which was consistent with the change trend of soil urease and phosphatase.Vegetation composition was affected by Sn content,function was affected by available Cr content,and vegetation species richness was affected by soil nutrient content.In terms of species availability,the similarity between soil seed banks and aboveground vegetation increased at the later stage of succession,but the similarity was still low,indicating that species availability of the community establishment was not entirely dependent on local seed banks,but also on the dispersal of surrounding vegetation.5.Bacterial communities responded more significantly to succession than fungal communities.The alpha diversity of bacteria increased after the first stage of succession,but there was no significant change in fungi.The enrichment of dominant taxa in bacterial communities at different stages was different,and Ascomycota and Basidiomycota were dominant phyla in fungal community at each stage.The resistance of microbial community increased significantly with succession,indicating that the community tended to be stable.The results of stepwise regression showed that the bacterial alpha diversity was mainly affected by oxidation reduction potential(ORP),and the community composition was affected by soil ionic properties(electrical conductivity(EC),p H,ORP).6.There were significant differences in ecosystem function in different succession stages.The multifunctionality of heavy metals was weakened and the multifunctionality of nutrient was increased.Microbial diversity and specific taxa affect the ecosystem function in succession.The rare taxa groups Dependentiae,Spirochaetes and WPS 2 in bacteria played an obvious role in reducing the multifunctionality of heavy metals,while bacterial diversity and most taxa affected the multifunctionality of nutrients in soil and had functional redundancy.Microbial prediction function also showed that the related functions of bacteria involved in C and N cycles have increased,and the cell repair function accounts for a higher proportion in the early stage of succession,while there was no significant change in various mycorrhizal fungi,which also showed that compared with fungi,bacterial community is main driving of succession and restoration.Previous researches on the restoration of abandoned mine mostly focused on the changes of plant communities under the condition of artificial restoration,while the research on their natural succession was relatively lacking.The natural succession of abandoned land is a spontaneous restoration process,exploring its mechanism and key influencing factors is great significance to understand the assembly of plant communities and the multifunctionality of ecosystems in mine abandoned land.By integrating the key characteristics and mechanisms of the natural succession process of plant communities,this study expounds the natural succession characteristics,community assembly mechanism,microbial assisted succession mechanism and key influencing factors of plant communities in abandoned metal mining areas,so as to provide a reasonable basis for the restoration of subtropical typical metal mines in Southwest Yunnan Province.