Effect Of Different Combination Of Phytoremediation On Soil Ecological Restoration At The Exploited Rare Earth Mine Site

In order to recover exploited rare earth mine area damaged in ecosystem,the rare earth mined land located at Huangshe Village,Renju Town,Pingyuan County,Guangdong Province,China,was used to study ecological restoration of phytoremediation with Miscanthus sinensis,Pinus massoniana and Bambusa textilis grown lonely or planted in mixture.The soil bacteria and soil physicochemical property changes,plant community succession,and their relationship were observed.16 S rDNA high-throughput sequencing were applied to study soil bacterial diversity.The main results were as follows:(1)Characteristics of plant community restored with different plantationOver three year natural succession after phytoremediation,there were more native plants appeared in restored plots,with 26 species,belonging to 17 families,24 genera.The tendency of plant polymorphism at different plantation plots showed mixed planting(Miscanthus sinensis + Pinus massoniana + Bambusa textilis)> Miscanthus sinensis planting > Pinus massoniana planting > Bambusa textilis planting.The plant community at the planting plots with Miscanthus sinensis planting and the mixed planting had the similar plant species.Miscanthus sinensis was their dominant plant,which had a strong adaptability in the site.Vegatation coverage in different slope land was more than seventy percent.Sunny-slope land was found higher plant polymorphism and succession toward to heliophytes.In the mixed planting plot,there were larger plants with higher biomass and soluble substance content.PCA analysis showed soluble sugar in Bambusa textilis could separate with other index,and soluble protein in Miscanthus sinensis and Pinu smassoniana could separate with other index.Morphological and physiochemical analysis showed the pioneer plants growed better in mixed planting than planting lonely.However,competition among different plants in mixed planting plot was adverse to Bambusa textilis growth with lower chlorophyll content.(2)Influence of different plantation on soilAfter phytoremediated for 3 years,soil pH at the restored land changed from strong acidity(pH 3.0)to neutral or weak acid(pH 6.0-7.1),so did the soil water(p H 6.0-7.1).The soil nutrients greatly increased,especially in the Miscanthus sinensis planting plot with soil organic and K content 3.34 and 4.38 times as much as the control,respectively.Heavy metal content in the restored soil and water was under the limitation of the national standard,and higher Mn,As and Al content than the national standard was found in the control.(3)Effect of phytoremediation with different plantation on soil bacterial communityThe results showd that Burkholderia,Ralstonia,Candidatus Koribacter,Candidatus Solibacter and Bradyrhizobium were with similar richness and as the functional bacterial genus to amixed planting plot.PCA of both unexploited plot and phytoremediated plots could separate from the control in the first-axle,with contribution value(PC value)of 93.9%.Phytoremediation improved the soil bacterial diversity and conserved most of the original bacteria before exploited.(4)Relationship of plant,soil and microorganism during phytoremediationAfter the pioneer plant growth improved soil physicochemical property,conserved soil fertility and water,more and more native plants join phytoremediation to further improve the soil.Thus,the microbial diversity and bacterial content increased.Increase of microbial diversity and bacterial activity made the soil nutrients increased,and the soil fertility increase would enhance plant growth.In short,the more plant growth and higher plant polymorphism,the more bacteria content and higher bacterial diversity,thus,the richer soil fertility.Differences could be observed in different plantation plots.