Effect Of Perennial Ryegrass And Leymus Chinensis On Rhizosphere Microbes In Petroleum-conta Minated Saline-alkali Soil

Soil pollution caused by petroleum and saline has become one of the serious environmental problems, it has been paid more and more attention. In this study, we performed a greenhouse pot-culture experiment to investigate the potential of plant Lolium perenne L.(Ryegrass) and Leymus chinensis in remedying PHCs-contaminated saline-alkali soils from the Daqing, in China. In the 2 months after the growth of plants, we analyzed the species diversity, functional diversity, structural diversity of rhizosphere microbes by use of dilution plate, Biolog Ecoplate, PCR-DGGE and 454 pyrosequencing. Moreover, we measured the activity of soil enzyme and the degradation rate of petroleum hydrocarbon under different oil concentrations. The main contents are as follows:1. The dilution plate culture method was applied to investigate the influence of plant Ryegrass and Leymus chinensis on the number of rhizosphere microbes under different oil concentrations in the saline-alkali soil. The results showed that under different oil concentrations, the number of bacteria and actinomycetes under Ryegrass and Leymus chinensis rhizosphere conditions significantly higher than that of the control soil. The number of fungus under Ryegrass and Leymus chinensis rhizosphere conditions was higher than that of the control soil, but only in the 10 g/kg oil concentration had significant difference. Compared with the two kinds of plants, the number of rhizosphere soil microbes(bacteria, actinomycetes and fungus) under Ryegrass rhizosphere conditions was higher than that of Leymus chinensis.2. The Biolog Ecoplate method was applied to investigate the influence of plant Ryegrass and Leymus chinensis on the functional diversity of rhizosphere microbes under different oil concentrations in the saline-alkali soil. The results showed that under different oil concentrations, the changes of AWCD value showed that the Ryegrass and Leymus chinensis were greater than the control soil, and the AWCD value of the Ryegrass had higher value and changed greatly; there was a significant difference in community functional diversity between the Ryegrass, the Leymus chinensis and the control soil; the microbial community functional diversity index showed that Simpson index and Shannon index were the Ryegrass, the Leymus chinensis and the control orderly, McIntosh index showed the opposite order, but there was significant difference between the plant and the control only at 10 g/kg oil concentration.3. The PCR-DGGE method was applied to investigate the influence of plant Ryegrass and Leymus chinensis on the structural diversity of rhizosphere microbes under different oil concentrations in the saline-alkali soil. The results showed that under different oil concentrations, the diversity and uniformity of the Ryegrass was higher than the Leymus chinensis and the Leymus chinensis was higher than that of the control soils. At 0 g/kg and 10 g/kg oil concentration, there were significant difference between the plant and the control; at 5 g/kg oil concentration, there were no significant difference. There were common bands between the Ryegrass, the Leymus chinensis and the control soils, but the band intensity of each were not identical; the Ryegrass and the Leymus chinensis had specific bands, belonged to Bacillus sp., Acidobacteria, Proteobacterium and Uncultured bacterium.4. The pyrosequencing was applied to further study the effects of plant Ryegrass and Leymus chinensis on the structural diversity of rhizosphere microbes under different oil concentrations in the saline-alkali soil. Under different oil concentrations, pyrosequencing showed that rhizosphere soil microbial biodiversity is far more than the understanding of people. At the phylum, class and genus levels, the Ryegrass and the Leymus chinensis increased the number of bacteria and changed the community structure of bacteria and fungi in the soil. Moreover, there is a large proportion of the unknown bacteria need to be studied.5. The urease activity, sucrase activity and dehydrogenase activity was investigated to study the effects of plant Ryegrass and Leymus chinensis on the soil enzyme activity under different oil concentrations in the saline-alkali soil. The results showed that under different oil concentrations, urease activity, sucrase activity and dehydrogenase activity of the Ryegrass and the Leymus chinensis significantly increased. Moreover, Soil enzyme activity of Ryegrass was higher than that of Leymus chinensis.6. The degradation rate of petroleum hydrocarbon was investigated to study the effects of plant Ryegrass and Leymus chinensis on petroleum hydrocarbon degradation under different oil concentrations in the saline-alkali soil. The results showed that in the 2 months after the growth of plants, Ryegrass removed 38.23% and 27.70% of the petroleum under 5 g/kg and 10 g/kg oil concentrations, respectively; Leymus chinensis removed 29.41% and 16.16% of the petroleum under 5 g/kg and 10 g/kg oil concentrations, respectively. Moreover, the degradation rate of Ryegrass is better than that of Leymus chinensis.