Effect Of Planting Transgenic Bt Cotton On Soil Enzymatic And Microbial Activities

Transgenic Bt cotton has been one of the most popular transgenic Bt crops in China. With increasing arable soils grown with Bt cotton, its impacts on soil environment have received more attentions due to the potential ecological risks by releasing Bt protein through root exudates, pollen or plant residue. Pot and field experiments were conducted to investigate effects of planting transgenic Bt cotton (cv Sukang 103) or non-Bt cotton (cv Sumian12) on soil enzymatic activities, and to compare the differences in enzymatic and microbial activities between rhizospheric and non-rhizospheric soils. The tested field was located at Yancheng, Jiangsu Province, China. Soil samples were collected at seedling, squaring, flowering-boll and boll-opening stages, respectively, to determine soil respiration, microbial biomass C and N, N net mineralization rate, and soil enzymtic activities including soil sucrase, dehydrogenase, alkaline phosphatase, urease and protease. The main results are presented as below:Under greenhouse or field conditions, planting transgenic Bt cotton increased the activities of soil sucrease, dehydrogenase and protease, but decreased urease activity in the rhizospheric soil. Furthermore, Bt cotton increased alkaline phosphatase activity under greenhouse conditions, in contrast, decreased it under field conditions but the difference was not significant. Microbial biomass C and N were enhanced with planting transgemc Bt cotton during the entire growth periods. Soil respiration and N net mineralization rate in rhizospheric soil of Bt cotton were significantly higher than that of non-Bt cotton at flowering-boll stage. Throughout the growth stages, soil enzymatic activities, microbial biomass C and N, soil respiration and N net mineralization rate showed similar tendencies in rhizospheric and non-rhizospheric soils grown with transgenic Bt cotton or non-Bt cotton, irrespective of pot or field experiment.During the entire growth periods, soil biological parameters were influenced on some degree with planting transgenic Bt cotton, but the influence was changed with growth stages. The above findings were just obtained from pot and field experiments with one-year duration, further researches are therefore necessary to monitor the long and cumulative effects of planting transgenic Bt cotton on C and N transformations in the field with fixed location.