Effects Of Transgenic Bt Cotton On The Ecological Characteristics Of Soil Microorganism In The Cotton Region Of Yellow River Basin

Transgenic Bt crops are widely planted around the world. With the quickly development and extension of genetically modified crops, it is needed to make a deep study on the effects of Bt crops on soil ecosystem. Since 1996, the transgenic Bt cotton expressed Bacillus thuringiensis (Bt) insecticidal crystal protein have been commercialized in a large scale in China. In this paper, there are test base in four provinces of the cotton region of Yellow River basin as a platform(Northwest A & F University, Shaanxi Province, test base; Cotton Research Institute, Shanxi Academy of Agricultural Sciences; Chinese Academy of Agricultural Sciences(CAAS)Institute of plant protection(IPP)in Hebei Langfang Experimental Station and Shandong Cotton Linqing Experimental Station Research Center), to study the effects of planting of transgenic Bt cotton on the rhizospheric soil microorganism, available nutrient contents and enzyme activities at four growth stages,30,60, 90,120 days after sowing.The mainly results are as follows:1. Traditional culture-dependent method was used to investigate the amount of microorganism. In the same province and at the same growth stage, no significant difference was observed in the amount microorganism in rhizospheric soil of transgenic and non-transgenic Bt cottons. Within the same province, the amount of microorganism was mainly affected by the growth stages; while in the different provinces, it was greatly affected by the regional conditions.2. The rhizospheric soil bacterial diversity was analyzed by applicated PCR-DGGE technology.In the four provinces, the bacterial diversity in rhizospheric soil of transgenic Bt cotton was abundant, and in the same province and at the same growth stage, there was no significant difference in the Shannon index, evenness and richness of bacteria in rhizospheric soil of transgenic and non-transgenic Bt cottons. In different provinces, bacterial diversity in rhizospheric soils was dependent on regional conditions, but the difference was rather small.3. The contents of microbial biomass carbon (MBC) and nitrogen (MBN) was studied by using fumigation extraction method. The results showed that, in four provinces, the microbial biomass carbon and nitrogen contents were different with each other at the growth stages. In four province, the rhizospheric soil MBC were significant difference between transgenic and non-transgenic Bt cottons at 60,90 days (P<0.05); the rhizospheric soil MBN were significant difference between transgenic and non-transgenic Bt cottons at 30,60,90 days (P<0.05). Within the same province, the contents of MBC and MBN were mainly affected by the growth stages; while in the different provinces, it was greatly caused by climate factor, soil types, years of planting and crop management practices.4. The results showed that, In the same province, the rhizospheric soil available nutrient:contents was mainly affected by the growth stages. The rhizospheric soil available nutrient contents in transgenic Bt cotton were significantly higher than that in non-transgenic Bt cotton in the same province at certain growth stage. The rhizospheric soil available phosphorus contents of transgenic Bt cotton were significantly higher than non-transgenic Bt cotton 39.02%,52.59% and 21.10% in Shaanxi, Hebei and Shandong Province at 120 day(P<0.05); The rhizospheric soil contents of nitrate nitrogen (NO3--N) of transgenic Bt cotton were significantly higher than non-transgenic Bt cotton 10.74%,28.00% and 52.58% in Shaanxi, Shanxi and Hebei Province at 120 day(P<0.05); And the rhizospheric soil contents of ammonium nitrogen (NH4+-N) of transgenic Bt cotton were significantly higher than non-transgenic Bt cotton 57.69% only in Shanxi Province at 120 day(P<0.05). While in the different provinces, it was greatly affected by the regional conditions.5. The results of soil urease activity and catelase activity showed that there was no significant difference between transgenic and non-transgenic Bt cottons in the same province at the same growth stage(P>0.05). The changes of cotton soil phosphatase activity were different in four provinces at different growth stages. The rhizospheric soil phosphatase activity were no significant difference between transgenic and non-transgenic Bt cottons in Shaanxi and Shanxi province at the same growth stage(P>0.05). In Hebei province, the rhizospheric soil phosphatase activity were significant difference between transgenic and non-transgenic Bt cottons at 30,60,90 days (P<0.05); In Shandong province, the rhizospheric soil phosphatase activity was significant difference between transgenic and non-transgenic Bt cottons at four growth stages.This paper preliminary study has found that the indicators of planting transgenic Bt cotton on the ecological characteristics of soil microorganism have been different in four provinces of the cotton region of Yellow River Basin. Within the same province, The measurement items were mainly affected by the growth stages; while in the different provinces, it were greatly caused by climate factor, soil types, years of planting and crop management practices.