Responses of soil enzymatic activities to transgenic Bacillus thuringiensis (Bt) crops - A global meta-analysis.

Transgenic Bacillus thuringiensis (Bt) crops have been widely planted, and the resulting environmental risks have attracted extensive attention. To foresee the impacts of Bt crops on soil quality, it is essential to understand how Bt crops alter the soil enzymatic activities and what the important influencing factors are. We compiled data from 41 published papers that studied soil enzymatic activities with Bt crops and their non-Bt counterparts. The results showed that dehydrogenase and urease significantly increased, but neutral phosphatase significantly decreased under Bt crop cultivations without Bt residues incorporation. The activities of dehydrogenase, β-glucosidase, urease, nitrate reductase, alkaline phosphatase, and aryl sulfatase significantly increased under Bt crop cultivation with Bt residues incorporation. The response ratios of other enzymes were not significantly changed. Generally, the response ratios of soil enzymes were greater with Bt residues incorporation than those of Bt crop cultivations without Bt residues incorporation. Further, the response ratios of soil enzymes varied with Bt crop types and growth periods. It was the strongest under Bt cotton among Bt crops, and the significant responses usually appeared in the middle growth stages. The responses of soil enzymes ascribed more to the properties of Bt crops than to soil properties across sites. Given - significant responses of some soil enzymes to Bt crops, we recommended that soil environmental risks should be carefully evaluated over the transgenic crops.