Effects Of Plant Growth-Promoting Bacteria On Energy Plant Growth And Cu Uptake In Contanminated Soil

Soil heavy metal contamination is becoming one of the most severe environmental issues, and phytoremediation is considered as a cost-effective and environment-friendly technology for remediation of heavy metal-contaminated soils. However, small biomass and slow growth for plant as well as the low bioavailability of heavy metals in soils limit the efficiency of phythremediation. Bacteria can promote plant growth. and increase heavy metal bioavailability and affect heavy metal accumulation of plants by many approaches thus facilitate phytoextraction by plants. Therefore, screening of plant growth-promoting bacteria, searching stable and effective energy plant-bacteria system and study the interaction between them were not only very meaningful in clarifying interaction mechanisms of plant and bacteria further, but also offer the theoretical basis and a new way for application of plant-microbe remediation.In this study,16strains characterized with production of indole-3-aceticacid (IAA) and siderophores were isolated from soil and Lespedeza of Tangshan copper mine wasteland. Further assessment on plant growth-promoting parameters revealed the16strains to produce ACC deaminase and solubilize insoluble phosphate. SAfter further selecting based on Characteristics such as production of ACC deaminase, mineral phosphate solubilization and nitrogen fixation, we screened strain TC1from soil and strain TGL2from Lespedeza tested positive for phosphate solubilization. Strain W33from bacteria kept in our laboratory showed positive ACC deaminase. Partial sequences of16S rRNAgene of PGPB obtained were matched against nucleotide sequences present in Genbank. The strains TGL2and W33were close to the members of the genus Rhizobium. Strain TC1showed high similarity with Arthrobacter sp.The isolated strains were tested for the ability to increase the water soluble Cu concentrations in solution culture containing Cu2(OH)2CO3and in soils. Results showed that strain TC1and strain TGL2could remarkably promote Cu2(OH)2CO3solubilization. Cu2+content in media was respectively increased to48.9mg·L-149.4mg·L-1, were remarkably enhanced by622.8%、630.6%compared with non-inoculated control respectively. Strain TC1and strain TGL2could also remarkably promote insoluble Cu of soil solubilization, and enhanced Cu2+content by47.3%、55.6%compared with non-inoculated control respectively.A pot experiment was conducted to elucidate the effects of inoculating PGPB on the plant growth and the uptake of Cu by alfalfa(Medicago sativa) in soil contaminated with Cu. The experiments clearly showed that two rhizobium strain TGL2and strain W33could remarkably promoted alfalfa growth; shoots dry weight and roots dry weight of alfalfa inoculated with strain TGL2were respectively183.8%、214.4%higher than that in control; shoots dry weight and roots dry weight of medicago sativa inoculated with strain W33were respectively243.5%、269.3%higher than that in control. The Cu uptake in alfalfa inoculated with strain TC1strain TGL2and strain W33were28.8%、231.%、258.7%remarkably more than that in control respectively.It was indicated that the tested strains could promote growth of seedlings of Brassica napus and hybrid pennisetum. So another soil pot experiment was arranged to researching the effect of the tested strains on growth and Cu accumulation of Brassica napus and pennisetum with copper stress. Experimental results indicated that the effect of bacterial inoculation on biomass and Cu content of Brassica napus was better than that of pennisetum. Strain TC1and strain W33could significantly increase upside dry weight of rape by24.6%、26.5%, roots dry weight of rape by25.0%、24.6%respectively. Cu2+content of roots of rape inoculated with strain TC1was significantly increased by24.0%; Cu2+content of upside and roots of rape inoculated with strain W33was significantly increased by24.2%、37.1%respectively. The total Cu uptake of rape inoculated with strain TC1and W33were39.7%and59.1%more than that in control respectively.Physiological characteristics of Brassica napus and physical and chemical properties of rhizosphere soil were determined. The results indicated that all of three tested strains could significantly increased the content of water-soluble K in rhizosphere soil of Brassica napus. Inoculation with Rhizobium sp. W33resulted in significantly increased relative chlorophyll content in rape leaves. The content of malic acids and succinic acid in roots of rape inoculated with Arthrobacter sp. TC1was significantly increased by393.7%and341.9%compared with controls respectively; the content of citric acid in roots of rape inoculated with strain TGL2was significantly increased by299.5%compared with controls. Besides, the content of succinic acid in roots of rape inoculated with strain W33was significantly increased by438.2%compared with controls. Strain TC1could significantly increase the content of water soluble Cu in rhizosphere soil of Brassica napus.Effect of the tested strains on bacterial community structure of the rhizosphere soil and roots of Brassica napus was researched by PCR-DGGE analysis. The results showed that all tested strains could colonized in rhizosphere soils and roots of Brassica napus. The bacterial community in the roots of rape was influenced more obviously by the tested strains compared with the rhizosphere bacterial community of rape. Proteobacteria. Firmicutes, Acidobacteria and Actinobacteria were dominant groups of bacterial in the rhizosphere soil and roots of Brassica napus.