The Effects And Mechanisms Of Plant Growth Promoting Bacteria Rhizobium Sp.T1-17 On The Subduction Of Heavy Metals By Vegetables

Microbial remedation was a kind of technology to remediate heavy metal-polluted soils.The growth and heavy metal tolerance of plants can be enhanced by microbes through a variety of pathways.Turf,vermiculite and other organic soil amendments could reduce the transfer of heavy metals to plants through adsorption of heavy metal elements.The solid microbial agent which was made of microbes and organic soil amendments could effectively reduce the paint absorption of heavy metals,achieving safe use of polluted soil.Screening the heavy metal resistant plant growth promoting bacteria(PGPB)could enrich the resources of PGPBs and provide remedating materials for safe use of heavy metal contaminated soils.Two hundreds and twenty strains were isolated from the lead-zinc tailings in Qixia Mountain and the copper tailings in Tang Mountain.Among the 220 strains,78 strains can produce indole-3-acetic acid(IAA),19 strains can produce siderophore.Eighty four strains were found to possess resistance to multi-heavy metals and plant growth promoting factors.According to the plant growth-promoting properties,heavy metals resistance and 16S rDNA phylogeny status,6 strains(Pseudomonas sp.G4-19,Bacillus sp.Q20,Paenibacillus qingshengii S1-9,Pseudomonas sp.S1-16,Chryseobacterium sp.T1-6,Rhizobium sp.T1-17)were selected to perform pot experiment using the contaminated soil collected from Qixia Mountain.The biomass and heavy metal content of the seedlings of Chinese cabbage,chilli and radish were detected.The results showed that only strain T1-17 could increase the biomass of these three vegetable seedling and reduce the heavy metal contents.Strain T1-17 increases the biomass of Chine.se cabbage and radish by 64.6%and 127.3%.Cd concentration of Chinese cabbage,chilli and radish inoculated with strain T1-17 were decreased by 22.1%,26.7%and 33.4%,respectively;and Pb concentration of Chinese cabbage,chilli and radish inoculated with strain T1-17 were decreased by 59.1%,15.5%,44.0%respectively,compared to the control.We prepared solid microbial agents with strain T1-17 and the adsorbent vermiculite,turf and biochar.The effects of strain,adsorbents and solid microbial agents on the yield and heavy metal content of the three vegetables were evaluated.The results showed that different treatments were able to increase the yield of three vegetables by 33.4%-334.1%;while reducing the Cd concentrations of edible parts of vegetables by 11.9%-87.0%and Pb concentrations by 30.1%-87.3%,compared to the control.The effect of different treatments were solid microbial agents>strain T1-17>adsorbents(vermiculite,turf and biochar).Analysis showed that strain T1-17 can stably colonize the potting soil.Different treatments of strain T1-17,adsorbents and solid agents significantly increased the chlorophyll content in leaves of Chinese cabbage and chili and the organic matter content in the rhizosphere soils by 39.6%-455.6%at the same time,compared to the control.The proportion of IAA-and siderophore-producing strains also showed an increasing trend in the rhizosphere soils.These results might explain the mechanism that different treatments could increase biomass of vegetable seedlings and yield of vegetables.In addition,different treatments also significantly decreased the water soluble,exchangeable,DTPA-extractable heavy metals' concentrations of rhizosphere soils.Analysis of potting soil aggregates showed that different treatment also promoted large particle aggregates(>2 mm)change to micro-aggregates(<0.25 mm),increased the heacy metal adsorbability of the soil particles.This suggests that different treatments may reduced the bio-availability of heavy metals through different ways such as adsorption and microbial conversion.