The Effect Of Plant Growth-promoting Bacteria (PGPB) And CO₂ On Cs Uptake By P. Americana Linn. And A. Cruentus L. And Related Mechanisms

Rapid development of nuclear industry and nuclear technologies in past few decades, nuclear explosion experiments or nuclear leakage accident, radionuclides have made the environment inevitably, posing potential harm to the ecological environment and human health. Due to long half-time and high uptake rate ¹³⁷Cs was considered to be one of the most dangerous radionuclides. As for treatment of radionuclides pollution, the conventional physical and chemical and engineering methods cost high, secondary pollution, and diffical in treating large scale. With the development of modern bio-technology, the bio-remediation of the radionuclide is receiving more attention. The bio-remediation includes microorganism remediation and phytoremediation. There are many anti-radionuclide microorganisms in the nature, and some of them could accumulate and precipitate the radionuclide. Microorganism remediation is used in treatment of the wastewater nuclear power station, whereas, phytoremediation is widely used in the soil contamination with good performance. However, phytoremediation has some disadvantages, such as low efficientyand long period. Therefore how to increase the plant biomass in the per-unit area and the uptake of the radionuclides in order to improve the remediation efficiency is receiving attention. On the other hand, we are facing atmospheric CO₂ rise which is considered to be one of the major environmental problems. It is universally acknowledged that, elevated atmospheric CO₂ effect of enhance the mineral nutrient uotake by plants, and improve growth. So, the study of the increasing CO₂ concentration on plant uptake of heavy metal or radionuclides, increasing remediation efficiency has becomes a new hot research topic.With the inspiration of elevated CO₂ as an asisitend remediation agent, the present paper use one growth-promoting bacteria Burkholderia sp.D54, this micro-organism is heavy metal (Pb, Cd, Cu and Zn) resistence and plant growth hormone production, nitrogen fixation, dissolving of inorganic phosphate. We investigated is Cs resistance and accumulation ability, we also investigated the Cs uptake effect of elevated CO₂-plant-microorganism combination, and the possible mechanism through plant root morphology, the uptake potassium, photosynthetic rate, The content of chlorophyll, activities of antioxidase and so on. The main conclusions are as follows:(1)The heavy metal resistance bacteria Burkholderia sp.D54 showed the tolerence to Cs, and could growh in the culture medium with the content of Cs 50mM; in the 100 mL culture medium, inoculated in 1 mL mother liquor(1.8×10⁷cfu·mL^-1), after 3 days produced the 0.1737g bacteria dry weight. The cell of Burkholderia sp.D54 was able to accumulate large quantities of Cs, being up to 45±3.85 mg·g^-1(dry weight), and the removing rate of Cs was 58.77% after 3 days.(2)after the 4 days inoculation Burkholderia sp.D54 could secrete large quantities organic acid with pH being down from 6.5 to 2.5; inoculation in the mica culture medium, show that the microgrgainsm could dissolve the potassium efficiently, leading to increasing potassium concentration efficiently.(3)Inoculation of the bacteria to the hydroponic A. crenentus, could increase the A. crenentus biomass and the absorption of Cs, but most of them are not significantly. The resistance index and enrichment coefficient were improved, and the remediation efficiency to some extent. The antibiotic ampicillin affected the growth of A. crenentus, in the plant and bacteria combined experiment, added ampicillin as the CK treatment, different effect on the different plant, should do the plant effect experiment first.(4)In the soil pot experiment in the ambient CO₂, inoculation of Burkholderia sp.D54, increased the total biomass of P. americana and A. crenentus (dry weight) by 19.8%³3.4% and 22.9%⁷6.6%, respectively. Elevated CO₂, increased the total biomass of P. americana and A. crenentus by 22%¹39% and 14%²54%, respectively.(5)In the pot experiment under the ambient CO₂, inoculation of Burkholderia sp.D54, increased the Cs concentration in shoot of P. americana and A. crenentus by 4.9%²2.4% and 8.1%¹9.4%, The Cs concentration in root was increased by 6.8%¹5.7% and 1.1%¹0.8%, respectively. Under the elevated CO₂, Cs concentration in shoot of P. americana and A. crenentus increased by 10%⁴7% and 32%⁴6%, whereas in root of P. americana and A. crenentus by 27%⁵6% and 35%³8%, respectively.(6)Cs in the soil inhibited plant of uptake potassium, that has function of participation of in plant chlorophyll synthesis, and therefore affect the content of chlorophyll and photosynthetic rate. Under ambient CO₂ and elevated CO₂, inoculation of Burkholderia sp.D54 improved the plant uptake potassium, and increased the content of chlorophyll, enhanced the plant net photosynthetic rate Pn, stomatal conductance (Gs), intercellular CO₂ concentration (Ci) transpiration rate (E) and water use efficiency (WUE), the increased of the biomass might contribute to these effection.(7)Under the stress of Cs, MDA concentration in leaves of P. americana and A. crenentus was significantly increased; Under ambient CO₂ and elevated CO₂, inoculation of Burkholderia sp.D54 inceresed Antioxidant SOD,CAT,POD enzyme activities of P. americana and A. crenentus, but decreased MDA contents in leaves of P. americana and A. crenentus .