Effect Of Elevated CO₂ On Uptake Of Cs By Phytolacca Americana Linn And Amaranthus Cruentus L. And Microbial Characteristics In The Rhizosphere

Since the mid-20th century, with the development of nuclear industryd and nuclear technology, soil contamination with radionuclides has widespread all over the world and became worse and worse. Science the phytoremediation has more advantages than other traditional technologies, it has been widely used in the remediation of radionuclides contaminated soils. However, phytoremediation also has some shortcomings. The bottleneck problem is how to improving the plant's biological traits to enhance the relative phytoremediation efficiency.In this paper, we used open-top chambers (OTC) to investigate the effects of elevated CO2 (860μL L-1) on biomass, cesium (Cs) uptake and soil rhizosphere microorganisms of Phytolacca americana Linn.and Amaranthus hypochondriacus L. growing on soils spiked with various levels of Cs (0, 100, 300, 500 and 1000 mg kg-1). The results showed that compared to the ambient CO2, elevated CO2 significantly increased the height, aboveground and underground biomass of P. americana L. and A. hypochondriacus L. by 6-24%, 3-30%, 6%-56% and by7-15%, 6-20%, 6-22%, respectively. Elevated CO2 significantly increased the uptake of cesium in the aboveground and underground of P. americana Linn. and A. hypochondriacus L. with maximum increase rate being up to 41%, 60% and 27%, 22%, respectively, implying improvement of phytoremediation efficiency. By comparing the Cs ccumulation, bioaccumulation factor and phytoextraction efficiency of P. americana L. and A. hypochondriacus L., respectively, it can be found that for the elevated CO2 concentration P. americana L. and A. hypochondriacus L. has the best phytoremediation efficiency when the soils spiked with Cs of 100-500 mg kg-1, and P. americana L. has a better phytoremediation efficiency than A. hypochondriacus L. In this paper we also found that elevated CO2 could also significantly increased the number of bacteria by 19%-32%, actinomycetes by 41%-21%, fungi by 25%-58% and microbial biomass C, N by 2-9%,8-28% in the rhizosphere soils of P. Americana Linn., and increased the number of bacteria by 8%-21%, actinomycetes by 10%-37%, fungi by 16%-32% and microbial biomass C, N by 8-22%,12-17% in the rhizosphere soils of A. hypochondriacus L. For the same level of CO2 concentration, there is significant correlation between the numbers of microorganisms and total biomass of P. americana Linn., but the correlation between the numbers of microorganisms and total biomass of A. hypochondriacus L. is not significant.