Meijun Zhang;Meichen Feng;Lujie Xiao;Xingyu Song;Guangwei Ding;Wude Yan

College of Agriculture, Shanxi Agricultural University, Taigu 030801 (China;College of Agriculture, Shanxi Agricultural University, Taigu 030801 (China);Department of Chemistry, Northern State University, Aberdeen SD 57401 (USA)

cry1ac protein;the field;soil microbial communities;transgenic bt;carbohydrates;functional diversit

The persistence of Cry1Ac protein in the soil and its effect on soil microbial communities are a core issue in assessing the ecological risk of transgenic Bacillus thuringiensis (Bt) cotton. In this study a field experiment was conducted on the cultivation of transgenic Bt cotton (Jin 26 and BtJi 668) with the immediate returning of residues to the fields, in order to quantify the CrylAc protein content in the fields and investigate its effects on the functional diversity of soil microbial communities. CrylAc protein in the residue-soil mixture was gradually degraded in the transgenic Bt cotton fields. After transgenic Bt cotton straw was returned to the fields for 30 d, 63.73% and 58.33% of the initial amounts of CrylAc protein were degraded in the Jin 26 and BtJi 668 fields, respectively. Before the crops were sown in the following year (180 d after returning the straw), no CrylAc protein was detected in the fields. After returning the cotton straw to the fields for 30 d, the Shannon-Wiener and McIntosh indices of soil microbial communities in the transgenic Bt cotton fields were significantly higher than those in the non-transgenic cotton fields. Meanwhile, the utilization of carbon sources including amino acids, amines, and carbohydrates by the soil microbial communities significantly increased. Both the McIntosh index and the utilization of carbohydrates increased until 180 d. Principal component analysis revealed that amino acids, amides, and carbohydrates were the main carbon sources distinguishing the two principal component factors. These findings indicated that CrylAc protein did not accumulate in the fields after transgenic Bt cotton was planted for one year and the residues were immediately returned to the fields; however, the original functional diversity of soil microbial communities was affected continuously.