| Due to the ever increasing factors that affect adversely the output of cotton, higher requirements are posed on cotton’s capability of resisting adverse elements, hence generates genetically modified cotton for better resistance against stresses. The growing of transgenic stress resistant cotton raises great concern among the people about its influence on soil ecosystem and, consequentially, on soil ecological environment safety. In consideration of the above,3 types of transgenic stress resistant cottons (transgenic salt-tolerant cotton, transgenic disease resistance cotton, transgenic drought resistance cotton) and their traditional counterparts were investigated in the study described in this paper. Soil samples were taken from within a rhizosphere of about 20cm in 5 growth periods (seedling stage, squaring stage, flower and boll stage, boll-opening stage and old stage) for two consecutive years. The soil samples were examined, using the traditional as well as PCR-DGGE-cloning analysis techniques, for their variation pattern of content of readily available nutrients, of enzymic activity, and of microbe diversity as influenced by the plantation of transgenic stress resistant cotton for two consecutive years. The analysis helped discover the impact that growing transgenic stress resistant cotton for two consecutive years on the 3 biological indicators. The main results showed that:1.The effects of three different of transgenic stress resistance cottons and their conventional cottons for two years in a row planting on soil available nutrients content with different growing stages, planting years and cotton varieties. Compared with their conventional cottons, three kinds of transgenic stress resistance cottons for two consecutive years of plangting on soil available nutrients had no significant effect except individual growth. The analysis about soil available phosphorus content found that except the transgenic salt-tolerant cotton in the squaring stage and flower and boll stage of 2015, the transgenic disease resistance cotton in the seedling stage and boll-opening stage of 2014, the transgenic drought resistance cotton in the seedling stage of 2014 on soil available phosphorus content is significantly lower than that of its conventional cotton, the other stages had no significant difference. The analysis about soil ammonium nitrogen and nitrate nitrogen found that the transgenic salt-tolerant cotton on soil ammonium nitrogen content in the seedling stage of 2015 and the squaring stage of two years and on soil nitrate nitrogen content in the seedling stage and flower and boll stage of 2014 are significantly higher than that of its conventional cotton, the other stages had no significant difference; There was no significant difference between transgenic disease-resistant cotton with its conventional cotton on the soil ammonium nitrogen content for two years in a row, but on soil nitrate nitrogen content is significantly higher than that of its conventional cotton in the seedling stage of 2014; the transgenic drought resistance cotton on soil ammonium nitrogen content in the seedling stage of 2014 and on soil nitrate nitrogen content in the seedling stage of two years in a row are significantly higher than that of its conventional cotton, the other stages had no significant difference.2.Transgenic salt-tolerant cotton on the soil urease activity was significantly higher than that of its conventional cotton in the seedling stage of 2014 and the old stage of 2015, on the alkaline phosphatase activity was significantly lower than that of conventional cotton in the squaring stage of 2015, and on the catalase activity was significantly higher than that of its conventional cotton in the seedling stage of 2015, while three kinds of enzyme activity was no significant difference in the other stage; Transgenic disease resistance cotton on the soil urease activity was significantly lower than that of its conventional cotton in the seedling stage, the squarding stage, the old stage of 2014 and the boll-opening stage of 2015, and on the catalase activity was significantly higher than that of its conventional cotton in the boll-opening stage of 2014, the other stage of three kinds of enzyme activity was no significant difference; There was no significant difference between transgenic drought resistance cotton with its conventional cotton on the catalase activity and the alkaline phosphatase activity in the five growth stage, excpt on the soil urease activity of transgenic drought resistance cotton was significantly higher than that of its conventional cotton in the seedling stage of 2014. The difference between the three transgenic stress resistance cottons and their conventional cottons on the activity of soil enzyme for two years in a row with different growing stages, planting years, cotton varieties and types of enzyme.3.The cluster analysis of DGGE fingerprints showed that the soil microbial community structure of three kinds of transgenic stress resistance cottons and their conventional cottons for two years in a row planting were relatively similar (the similarity is greater than 60 degrees basically) in different growing stage. The digital analysis of DGGE fingerprints found that except the transgenic salt-tolerant cotton in the seedling stage and old stage of 2015, the transgenic disease resistance cotton in the flower and boll stage of 2014 and old stage of 2015, the transgenic drought resistance cotton in seedling stage and boll-opening stage of 2015 and the squaring stage and old stage of 2015 on soil shannon-wiener index, evenness and richness showed significantly higher than their conventional cottons, the other growth stage had no significant difference. With the different of growth stage, the soil shannon-wiener index, evenness and richness of three kinds of transgenic stress resistance cottons and their conventional cottons were different, its showed that the changes of the soil microbial diversity and community structure were not significantly influenced by planting of the three kinds of transgenic stress resistance cottons for two years in a row, but the greatly influenced by planting year and growth stages. The main bands of DGGE fingerprints by tapping, recycling, cloning and sequencing showed that the soil microbial community composition of three kinds of transgenic stress resistance cottons and their conventional cottons for two years in a row were similar, this accord with the results of cluster analysis, and this homologous sequences mainly belongs to Proteobacteria, Bacteroidetes, Acidobacterias, Actinobacteria, Firmicutes and Nitrospirae, among them, the more distribution of the Actinobacteria and Proteobacteria.This paper provides a preliminary study which investigated the effect of growing 3 types of transgenic stress resistant cottons and their traditional counterparts for 2 consecutive years on the content of readily available nutrients, enzymic activity, and microbe diversity in soil. The results demonstrated that, for all the 3 types of transgenic stress resistant cottons and their traditional counterparts, the content of readily available nutrients, enzymic activity, and microbe diversity vary in a way that is intimately related to cotton plantation duration, growth period, and species and further that when compared with the case of traditional cotton the influence of growing the 3 transgenic species on the content of readily available nutrients, enzymic activity, and microbe diversity is not great. However, long-standing monitoring and testing of various biological indicators are necessary in order to substantiate that the 3 types of transgenic cottons produce minimal influence on soil as a result of their plantation. |
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