An Analysis Of The Amending Effect Of Bacteria-organic Manure On Mn Minging Wastes Contaminated Soil And Characteristics Of Rhizobacteria

A set of on-site simulation devices using Mn tailing wastes from Xiangtan Mn mining area as plant growth medium was designed to examine the amending effect of an organic manure containing a tolerant bacterium strain isolated from the tailing wastes.The phytoremediation effects of single and multiple tree species(Koelreuteria paniculata,Paulownia.,Ligustrum quihoui Carr.,Nerium indicum Mill.,Phytolacca acinosa Roxb)models as well as their heavy metal(Mn,Pb,Cu,Zn,Cd)uptake and accumulation characteristics were compared at pilot-scale test levels using the established simulation devices.High-throughput microscopy 16S rRNA and 18S rRNA gene amplicon sequencing techniques were applied to analyze the composition and structure of the microbial community in the rhizosphere with purpose to determine the main factors affecting the rhizospheric characteristics.The results obtained from the present srtudy will provide basic data for identifying the key rhizospheric microbial species that play specific roles in the process of heavy metal extraction by plants.The main results are as follows:(1)In the pilot-scale tests,the largest biomass quantity was obtained from the single plant species model while the heighest metal uptake quantity was found in the multiple plant species model.The order of tested plants biomass was:Koelreuteria paniculata>Paulownia>Ligustrum quihoui Carr>Phytolacca acinosa Roxb>Nerium indicum Mill.The Mn accumulation of the multiple plant species model was 2.7 times that of the single species model.The order of Mn uptake quantity among tested plants was:Paulownia>Koelreuteria paniculata>Phytolacca acinosa Roxb>Ligustrum quihoui Carr>Nerium indicum Mill.The results showed that Koelreuteria paniculata and Paulownia can be used as woody plants for the restoration of manganese-contaminated soils in combination with the application of bio-organic manure.(2)Compared with control treatment,application of organic manure caused a slight increase in water soluble manganese content but a significant decrease in chelating-exchangeable manganese content in the substrate.The results showed that the organic manure amending had apparently a positive effect accounted for not only by enhanced plant growth and heavy metal uptake but also by improved substrate water retention capacity and reduced heavy metal diffusion rates.Among the tested phytoremediation treatments,the multiple plant community-organic manure amending was shown to be the best ecological restoration model as it gave the highest values of plant coverage and biodiversity indices and lowest soil and water loss rates.(3)Application of organic manure had a positive effect on species diversity and richness of rhizosphere bacterial community in both single and multiple tree species plots.The dominant bacterial phylum was Proteobacteria,and the dominant classes were Proteobacteria and Anhydride.Except for direct introduction of new bacterial species by organic manure application,the positive effect of the manure amending could be further attributed to the improvement of the rhizospheric environmental conditions related to soil heavy metal toxicity,pH,moisture,and nutritional levels.The differences in soil bacterial composition,structure and dominant species were found insignificant between single and multiple tree species models,suggesting that the tested tree species had less specific influences on rhizosphere bacterial community than organic manure application.(4)Organic manure application also had a positive effect on diversity and richness of rhizosphere fungal community in both signle and multiple tree species plots.The relative abundance of Ascomycota and Basidiomycetes was significantly increased after organic manure application.Different from that observed for bacterial community,there were significant differences in relative species abundance of fungal community between single and multiple tree species models,showing that the diversity of plant community had a direct influence on the genetic diversity of soil fungi.This influence had been apparently enhanced by organic manure application.