不同生长期转Bt基因水稻秸杆还土对淹水土壤酶活性的影响

Enzyme activities variation in flooded soils amended with Bt transgenic rice straws at different stages of plant development

在实验室条件下通过秸杆还土试验比较了不同生长期转 Bt基因克螟稻及其亲本稻秸杆对淹水土壤酶活性的影响。研究结果表明 ,与同一生长期的亲本稻秸杆相比 ,孕穗期和成熟期克螟稻秸杆对淹水土壤磷酸酶活性的影响较小 ;相反 ,对淹水土壤脱氢酶活性的影响非常显著 ,并且孕穗期秸杆与成熟期秸杆的添加对淹水土壤脱氢酶活性的影响趋势也存在较大差异。推测造成淹水土壤脱氢酶活性的显著性差异的主要原因可能是由于 Bt插入基因表达的多效性所致。结果认为土壤脱氢酶活性可作为转 Bt基因水稻生态安全风险性评价的潜在指标。

The transformation of genes from Bacillus thuringiensis (Bt) that code for the production of insecticidal toxins into crops reduces the pollution associated with the application and run off of chemical pesticides, because the toxins are produced continuously within these plants. However, there is increasing concern that these crops may pose risks to natural and agricultural ecosystems. So far, most of the research has focused on upland crops, such as Bt corn, and Bt potato. No studies have been carried out on the effect of Bt transgenic rice on the biochemical processes in flooded paddy soil. In practice, rice straw is usually incorporated into soil to enhance soil fertility. As a result, toxins as well as other expressed foreign gene products may accumulate in soil and constitute a hazard to soil ecological processes. Soil enzyme activity has often been proposed to be an early and sensitive indicator of anthropogenic effects on soil ecology both in natural and agroecosystems. In the present study, we assessed the possible influences of Bt transgenic rice straw, from cultivar KMD, on dehydrogenase and neutral phosphatase activities in flooded paddy soil under laboratory conditions. Cultivar KMD was derived from a commercial Chinese Oryza japonica rice variety Xiushu 11, transformed with a synthetic cry1 Ab gene from B. thuringiensis and gusA, hph and nptII genes under the control of a maize spelling promoter. The experiments were conducted in plastic pots each containing 1500g air dried fluvio marine yellow loamy soil amended either with 3% (w/w) Bt transgenic rice straw or 3% (w/w) parental rice straw at the booting stage or at the maturing stage. Nine hundred mL sterile distilled water was added to submerge the soil. The flooded soils were then incubated in the dark at 28±1℃. Soil samples were taken from each pot at defined intervals over the incubation to assay for enzyme activity. Results showed that there were few significant differences in neutral phosphatase activity over the course of the incubation between soils amended with Bt transgenic rice straw and parental rice straw either at the booting stage or at the maturing stage. However, significant differences in dehydrogenase activities between soils amended with Bt transgenic rice straw and the parental rice straw were observed both at the booting stage and at the maturing stage. In addition, the trends of the changes of soil dehydrogenase activities over incubation time also varied. When soil amended with Bt transgenic rice straw at the booting stage, dehydrogenase activities were significantly higher on sampling days 7 and 14, and lower on sampling days 21, 30, 35 and 49 than those in soil that had parental rice straw added at the same stages, but there were no significant differences on sampling days 70 and 84. When treated with straw at the maturing stage, dehydrogenase activities in soil amended with Bt transgenic rice straw were significantly lower among sampling days 7 to 49, and higher on sampling days 70 and 84 than those in soil amended with parental rice straw. Soil dehydrogenase rice activity could be a potential index for risk assessment on the release of Bt transgenic rice in the environment.