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Agriculture, Ecosystems & Environment
Vol. 239, 2017, Pages: 154–160


Effects of the consecutive cultivation and periodic residue incorporation of Bacillus thuringiensis (Bt) cotton on soil microbe-mediated enzymatic properties

Zhenhua Chen, Kai Wei, Lijun Chen, Zhijie Wu, Junyu Luo, Jinjie Cui

Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China.

Abstract

Risk assessments of insecticidal Cry proteins from Bacillus thuringiensis (Bt) cotton in soils have been mainly based on microcosm and short-term experiments. There is a lack of longer-term field results, especially when Bt-cotton residues are incorporated into the soil. In this study, we used a six-year field trial to evaluate how cultivation duration and Cry1Ac-inputted modes of Bt-cotton affect the persistence of Cry1Ac proteins and soil microbe-mediated enzymatic properties. The results showed that the persistence of Cry1Ac proteins increased with cultivation duration and periodic residue incorporation of the transgenic Bt-cotton variety ZM41. Moreover, temporal residue incorporation had a relatively larger contribution to the persistence of Cry1Ac proteins in the soil than their release in the growth period. Regardless of Bt-cotton cultivation or residue incorporation, soil microbial biomass was significantly suppressed. However, the dehydrogenase activity was significantly stimulated in Bt-cotton cultivation but suppressed in residue incorporation. The activities of β-glucosidase, nitrate reductase, phosphomonoesterase and arylsulfatase were significantly stimulated in soils with Bt-cotton residue incorporation. Based on a structural equation model analysis, the change in enzymatic activity of these four enzymes was attributed to both a direct effect from Cry1Ac proteins and an indirect effect via dehydrogenase.

Keywords: Bt toxin; Cry1Ac proteins; Cotton tissue incorporation; Microbial biomass carbon; Soil enzyme activity.


 
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