Degradation Of Atrazine In Rhizosphere And Changes Of Soil Biological Indices In Phytoremediation

The soil in some regions of China is contaminated by the overuse of pesticides. Atrazine is one of the herbicides that is widely used in China. Phytoremediation is a method of clearing up pollutants from environment by plants. It has the advantages of Low cost, saving land resources and no secondary pollution. More importantly, it does not destroy the ecological environment. So it has a bright future for application to the purification of contaminated soil.Mulberry(Morus alba Linn), poplar(Populus deltoids cv. 1-69/55) and transgenic poplar(Populus deltoides×nigra, DN34) were taken as plant materials to remediate atrazine contaminated soil in the Research Geenhouse of Chinese Academy of Forestry in this study. The degradation dynamic of atrazine was studied in different rhizosphere environment with GC method; the dynamic variation of microbial biomass, microbial community structure and microbial activity were investigated with the purpose of elucidating the rhizosphere effects and mechnism of phytoremediation of Atrazine contaminated soil by transgenic poplar,in the process of phytoremediation, by means of PCR and DGGE combined with other conventional methods such as separating microbe, determinating microbial biomass carbon. The main results are summarized as follows:1. In the condition of 10mg·kg^-1 atrazine contaminated soil in greenhouse, the change in total amount of atrazine's residue with time met a kinetic equation C=C₀e^-kt in non-rhizosphere, and the half-life of atrazine is 58.48 days. Degradation rate declined during the sampling duation. The concentration of atrazine would change in mulberry rhizosphere; it was not significant in the effect of phytoremediation by poplar; transgenic poplar could clear up atrazine. It is the fastest in comparison with mulberry and poplar, and the associated mechanism remains to be studied further.2. The bacteria in non-rhizosphere soil with the initial concentration of atrazine 10mg.kg^-1 was significantly inhibited by atrazine. The number of bacteria in rhizosphere soil was more than that in non-rhizosphere soil. The number of bacteria in transgenic poplar rhizosphere soil remained stable, and was more than that in other rhizosphere soil on the whole. The numbers of fungi was stable both in non-contaminated soil and rhizosphere soil during sampling. The population of fungi was more in rhizosphere soil than in others showing much the same trend of change. The numerical ordination of actinomycosis was: non-contaminated soil＞rhizosphere soil＞non-rhizosphere soil.3. The contents of microbial biomass carbon declined sharply in rhizosphere and non- rhizosphere soil within a month in the initial concentration of atrazine of 10mg.kg^-1, while increased in various degree in rhizosphere soil during the period of from 30th day to the 60th day, of which, the fastest increase could be seen in the rhizosphere soil of poplar and transgenic poplar. Later after the 60th day, the contents of microbial biomass carbon declined again in rhizosphere soil. By contrary, since 30th day, the contents of microbial biomass carbon turned to be fairly low in non-rhizosphere soil and remained stable.4. Soil microbial quotient was influenced by application of atrazine. It had been low in non-rhizosphere soil and the slow increase of that could be seen since the 30th day. There was much similar tendency for the rhizosphere soil decreased in the first 30 days; increased from the 30th day to the 60th day; declined after 60 days. The ordination by soil microbial quotient in rhizosphere soil was: poplar＞transgenic poplar＞Mulberry.5. It was found that genetic diversity of microbial communities in transgenic poplar rhizosphere was different from that in non-rhizosphere soils by PCR and DGGE analysis.Non-rhizosphere soil: genetic diversitiy of microbial communities after 30 days was similar to that after 60 days; two specific bands could be found on the 60th day; microbial genetic diversity decreased significantly on the 90th day.Rhizosphere soil: genetic diversitiy of microbial communities after 30 days was similar to that in non-rhizosphere soil; two specific bands could not be found on the 60th day compared with nonorhizosphere soil; comparing with the non-rhizosphere soil, the level of diversity kept higher on the 90th day.