| Genetically Modified (GM) crops began to enter the field trials in 1986, it rapid developed with enormous social and economic benefits. Global transgenic crop area from 1.74 million hectares in 1986 to 185.1 million hectares in 2014, meanwhile, the potential environment of GM plant drawn great attention in the all world. Soil plays an important role in energy transformation, matter cycling, and information exchange of organism and environment in the ecosystem. And its healthy condition is closely related to the entire ecosystem. Whether genetically modified crops will affect the structure and function of the soil ecosystem? The research on this issue is necessary and imminent.In this study, tobacco was be taken as a model plant and wild type tobacco as a control, we carried out a pot experiment in three seasons about chitinase-transgenic (T-Chit) and non-transgenic (Nt-X) tobacco on rhizospheric soil ecosystem under continuous cropping in purple soil. The test include the following contents:the dynamic change of rhizosphere soil enzyme activity, Physical and chemical properties, rhizospheric soil microbial population and community structure of Nt-X and T-Chit in different life period of tobaccos; We extracted the rhizosphere soil extracts of two tobacco in stubble stage and analyzed the type and relative amount of its metabolites using GC-MS technology, metabolites isolated trend was analysed to determine the impact of continuous cropping of transgenic tobacco on root exudates; Rhizosphere soil total DNA of transgenic tobacco in the three year was extracted, PCR technique was used to detect the target gene is flow to soil or not. The main purpose of this study is to exploer the impact of transgenic tobacco on rhizospheric soil ecosystem under continuous cropping in purple soil, as well as the change of tobacco root metabolites in the process of cropping. The main conclusions are as follows:(1) Nt-X and T-Chit have no difference in agronomic characters, The change tendency of T-Chit was almost the same as its of wild type contrast under three years continuous cropping. In the first year, Plant height higher than the two later years; Leaf number、aboveground biomass、underground biomass in the second year less than the other two years. The main reason is environmental factors (temperature) affect the growing of tobacco.(2) There was no Significant difference in rhizosphere soil enzyme activity of Nt-X and T-Chit at all grow stages. Soil catalase activity of Nt-X is low during the rosette stage, then increased at flowering stage, this is consistent with growth trend of tobacco. The soil hydrogen peroxidase of T-Chit lower than Nt-X, however, there was no significant difference between two treatments; Urease activity ere the lowest in flowering, increased during stubble period, and it in the second year higher than in the first and third year; Protease activity of T-Chit was lower than Nt-X, and the difference was insignificant. Overall, Nt-X and T-Chit soil protease activity does not vary with changes of growth period, the differences between the different growth years was not significant, this indicating that soil protease activity is relatively stable in the whole growth time.(3) Determined of tobacco rhizosphere soil properties found soil organic matter, total K, pH in the first year greater than two years later, total K was significantly greater than other two years, this is because in the tobacco growing process organic matter was consumed gradually, while tobacco is a high-K plants, it will be missing K in the later with the growth of tobacco; Total N and P content is low in the first year, then increased with the planting time gradually, total N and total P in the third year was significantly greater than the first year; the change of T-Chit rhizosphere soil properties was the same as Nt-X, T-Chit rhizosphere soil total P and pH more than Nt-X.(4) Tobacco rhizosphere culturable bacteria population changed with variety of tobacco growth stages. During planting time, The CFU numbers of Nt-X and T-Chit increased at the flowering stage, and then decreased, the population at flowering stage was the highest in all three stages. For T-Chit, differences were found at the two later years, the number of bacteria lowered than Nt-X in the second and third year, the population of T-Chit, at flowering stage was the lowest in all three stages and diffenence significant; The consequences of this tests pointed that the number of fungi didn’t fluctuate within a growth seasons, the levels of fungi population at all three stages had remained stable; at the same time, experiment showed that the CFU numbers of fungi did not differ statistically between the transgenic plants and wild-type group in the most treatments, except for flowering stage in 1 season and 2season, the fungi number in T-Chit higher than Nt-X during flowering stage.Also, in the rhizosphere soil samples, the amount of fungi of Nt-X and T-Chit was 32.88×104cfu.g-1,34.58×104cfu.g-1 respectively, the results indicated that it is insignificant between transgenic and non-transgenic tobacco.(5) The concentration of total PLFA showed the same trend between Nt-X and T-Chit in three successive years, it increased with the extend of planting time. Compared with the first year, the rhizosphere soil microbial diversity and the number of dominant species increased, evenness decreased after two years planting, indicating that continuous cropping will increase the diversity and amount of tobacco rhizosphere soil microbes. Three diversity indices (Shannon’s, Simpson’s, Pielou) of Nt-X lower than T-Chit, but, three has no significant different between Nt-X and T-Chit in microbe diversity at all three diversity index T-Chit. These PCA analysis results showed that the original was clearly distinguished with others, but, Nt-X and T-Chit was clearly distinguished litter. All these conclusion revealed that plant time played an important role in bacterial community diversity, rather than the presence of transgenic and non-transgenic tobacco.(6) Extracts from rhizosphere soil of tobacco at stubble stage all contained 8 categories substances, that was, meywerehydrocarbons, lipids, acids, carbohydrate, ethers, amines, phenols, alcohols and so on.55 kinds in Nt-X, and 49 kinds in T-Chit. lipids, acids, carbohydrate was the main Metabolites in both two type tobacco. Octadecanoic acid was reported may be allelochemicals in all substances were detected, Its relative content in the Nt-X in three years were 0.70,2.16,2.63 respectively, T-Chit is 2.46,0.71,3.07 respectively, the conclusion was that the content of allelochemicals in root Metabolites of tobacco increased after continuous cropping; PCA analysis showed that the type and content of tobacco metabolic primarily related to planting years, the separation between the transgenic and non-transgene obscure.(7) After planting transgenic tobacco under continuous cropping in purple soil for three year, the target gene does not existed in soil total DNA, so, the target genes (Mcchitl) haven’t flowed to soil microbes. |
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