Effects Of Transgenic Soybean On The Genetic Diversity Of Nitrogen-fixing Microorganisms

Transgenic crops were grown in an increasingly large scale around the world, and accompanied by public concern about their potential ecological and environmental impacts. As one of the main transgenic crops, it is needed to make a deep study on the effects of transgenic soybean on soil ecosystem.As materials of the research, four genotypes’soybean including M88(CP4EPSPS), GTS40-3-2(CP4EPSPS), ZB (Bt crylAb+CP4EPSPS) and conventional soybean Zhonghuang13were compared in this study. The experiments were conducted in this study in order to investigate the effects of different transgenic soybean on the diversity of nitrogen-fixing microorganisms, the soil enzyme activities and nutrient contents at maturation period in pot experiments, using PCR-DGGE and DNA sequencing targeting nifH gene. The main results in the present study were as follows:1. Effects of transgenic soybean on nutrients and enzyme activities in rhizosphere soilThe results showed that compared to conventional soybean Zhonghuang13, the soil nitrate nitrogen, ammonium nitrogen, available phosphorus, total phosphorus and organic carbon of transgenic soybean M88, GTS40-3-2and ZB had no significant difference. It was no significant change rule in rhizosphere soil total nitrogen content among transgenic soybean and conventional soybean. The results of soil enzyme activities showed that there was no significant difference between transgenic soybean M88and conventional soybean (p>0.05). Compared to the conventional soybean, the planting of ZB showed no significant influences in soil activities of alkaline phosphatase and catalase, but urease activity decreased significantly; in addition to alkaline phosphatase activity, rhizosphere soil urease and catalase activities were significantly decreased by planting transgenic soybean GTS40-3-2(p<0.05).Cluster analysis showed that the changes of nutrients and enzyme activities in rhizosphere soil were mainly affected by soybean species, the impact of transgenic soybean on the main nutrients and enzyme activities was very limited.2. Effects of transgenic soybean on the genetic diversity of nitrogen-fixing bacteria in rhizosphere soilThe rhizosphere soil nitrogen-fixing bacterial genetic diversity was analyzed by applicated PCR-DGGE technology.The results showed the diversity indexes and evenness indexes between transgenic soybean M88, GTS40-3-2and non-transgenic soybean zhonghuangl3had no significant difference. Transgenic soybean ZB rhizosphere soil nitrogen-fixing bacterial diversity indexe was significantly higher than local major soybean zhonghuangl3, but evenness indexes had no significant difference. The results of cloned and sequenced showed in the rhizosphere soil of transgenic soybean and non-transgenic soybean sequences were belong to the a-proteobacteria, β-proteobacteria, y-proteobacteria, Cyanobacteria and Unknown. Among the18sequences,12sequences were of Proteobacteria, occupying62%of the total and showing in all area of the DGGE gel.3. Effects of transgenic soybean on the genetic diversity of rhizobiumThe rhizobium bacterial diversity was analyzed by applicated DGGE-cloning technology.The results showed the diversity indexes and evenness indexes between transgenic soybean M88, GTS40-3-2and non-transgenic soybean zhonghuang13had no significant difference. Transgenic soybean ZB rhizobium diversity indexe was significantly higher than conventional soybean zhonghuangl3, but evenness indexes had no significant difference. DGGE bands sequencing results showed that the potted soybean rhizobia symbiosis including Rhodospirillaceae, Bradyhizobiaceae, Rhizobiaceae and Uncultured.These results suggested that, relative to the influence of different soybean species, the transformation of CP4EPSPS and Bt crylAb genes into soybean didn’t cause any significant effect on the diversity of nitrogen-fixing microorganisms.