The Interactions Between AMF And Soil Bacteria And Their Functional Roles In The Enhanced Metal Tolerance Of Host Plant

Numerous reports repeatedly document that arbuscular mycorrhizal fungus,as one of the functional component of plant roots,play a key role in the bioaugmented tolerance of host plants against various stressed conditions.While,the effects of AMF colonization on the rhizosphere microbiota and their interactive functions are obscure under the multiple-metals polluted soil.In the current study,one representative AMF strain(Funneliformis mosseae)and the native soil microbiota were targeted and inoculated with their host maize Huidan 4#(Zea mays L.)in the multiple-metals(Pb,Zn and Cd)polluted arable soils in Huize county Yunnan Province,and the interactions between AMF and rhizosphere microbiota and their functional roles in the enhanced metal tolerance of host maize were comparatively studied in a greenhouse.At the same time,the environmental factors(soil physical and chemical properties,chemical forms of heavy metals and soil enzyme activities and etc.)of the rhizosphere soil microenvironment in the different treatments were also determined,and the diversity of the indigenous rhizosphere bacterial community under the condition of AMF inoculation was evaluated to explore the re-assembles of rhizosphere bacterial community shaped by AMF inoculation,and their interactive effects and the mechanism on the absorption and accumulation of heavy metals in maize.1.Compared with the treatments without microbial inoculation(M-B-),single AMF inoculation(M+B-)significantly reduced the uptake and accumulation of metals in both maize roots and shoots,and alleviated the maize phytotoxicity caused by excessive metal ions,and promoted the growth of host maize under the multiple-metals polluted arable soils.Conversely,single inoculation with indigenous rhizosphere microbiota(M-B+)enhanced the concentrations of DTPA-extractable Cd and Zn and acid-soluble Cd in rhizosphere soils,and promoted the uptake and accumulation of metals in both maize roots and shoots,inhibited the root development and caused the reduced growth of maize.Interestingly,there were synergy effects caused by the dual inoculation with both AMF and rhizosphere microbiota(M+B+)on the maize,with the maximum growth and the minimum metal accumulation,which were significantly different from the other 3 treatments(p < 0.05).2.Experimental results showed that the microbial inoculations,including both the single inoculations of AMF or rhizosphere microbiota and their dual inoculations,significantly changed the microenvironmental characteristics of rhizosphere soils.We found that the AMF inoculation significantly enhanced the concentrations of both available K and P,as well the dual inoculation treatments with the markedly higher p H values.Especially,the single bacterial inoculation caused the significantly higher concentrations of both DTPA-extractable Cd and Zn.While the dual inoculation treatments obviously reduced the concentrations of metal ions in the low-toxicity in rhizosphere soils,e.g.the significantly lower acid-soluble Pb,Zn and Cd than that in the single bacterial inoculation treatments.The Spearman analyses revealed that there were close correlations between the maize growth and metal accumulation and the altered values of rhizosphere soils,including soil p H,available P and K,acid coluble Pb,Zn and Cd.Our results showed that it was one of the most important strategy of plant adaptation to the stressed environments,e.g.metal-polluted soils.While such effects were dependent on the inoculant types.Especially,the functional roles were needed to be further studied during the interaction with rhizosphere microbiota.3.High-through sequencing data were used to evaluated the effects of AMF colonization on the community composition of rhizosphere microbiota,and found that there were distinct communities of rhizosphere bacteria colonizing dual inoculation with AMF and microbiota from the single bacterial inoculation,with a significantly higher ACE and Chao index in M+B+ treatments.In total,there were 11 bacterial phyla,which were significantly different between the two treatments,including the significantly increased and significantly reduced in M+B+ treatments than M+B-.Also there were 12 significantly different genera,and the marked increase of Unclassified?f?Gemmatimonadaceae,Bacillus,Subgroup?10,Ellin6067,norank?f?Vicinamibacteraceae and Unclassified?f?Microscillaceae in M+B+,as well as the increased Arthrobacter,Flavisolibacter,Massilia,Adhaeribacter,Streptomyces and Noviherbaspirillum in M-B+.Spearman analyses showed that the concentrations of DTPA?Pb,acid soluble?Cd/Pb/Zn,reducible?Pb,oxidizable?Cd/Zn,residual?Pb,AKP were the key environmental factors,which were closely correlations with the alternations of over 10 bacterial genera.Our results revealed that AMF colonization significantly changed the community composition of rhizosphere microbiota of host maize,and such alternations were also the solid evidence for the synergy effects of dual inoculations altered from the negative response on maize growth under multiple-metal polluted arable soils.Our results revealed that AMF colonization re-shaped the community composition of rhizosphere microbiota,which were significantly different from the single bacterial inoculation.And such alterations also changed their functions and showed synergy effects of dual inoculations from the negative response on maize growth under multiple-metal polluted arable soils,and finally contributed to the enhanced tolerance of their host maize against metal-stresses and promoted the maize growth.Our experimental data provide theoretical basis and technical support for improving the safe production of heavy metal polluted farmland soil via the use of mycorrhizal technology to activate and engineer the rhizosphere functional microorganisms.