Soil Ecological Safety Evaluation for Bivalent Transgenic Cotton Plants: Root Exudates versus Soil Enzyme Activities and Soil Microbial Diversity

Pot experiments were conducted to assess the possibly adverse effect of transgenic Btand CpTI-cotton (Bacillus thuringiensis and cowpea trypsin inhibitor cotton) on soil ecosystem. Soil enzymes activities and microbial molecular community and diversity based on 16sand 18s-PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) profiles were determined by adding root exudates of Btand CpTI-cotton into soil. Results showed that the root exudates of transgenic cotton seedlings increased the soil catalase activity by 21.8% to 32.7%. The soil urease activity was decreased by 11.0% while the activity in the treatment of 1ml/350g soil was increased by 18.1% compared to control. The invertase activity in the treatment of 1 ml/350g soil was increased by 54.2%, however, the activity in the treatments of 2 and 4 ml/350 g soil was decreased by from 25% to 29.2%. The total 16sPCR-DGGE lane bands of bacterial community and diversity were almost not different. However, the effect pattern of root exudates of transgenic cotton on soil fungal community and diversity was differed from bacteria. The fungal community number and composition were changed. Though some dominant community disappeared and other newly dominant community appeared, the fungal stability index was increased. Results suggested there was little significantly adverse effect of Btand CpTI-cotton on soil ecosystem.