Effect Of Bt Corn Straw Returning And Eisenia Fetida On Soil Greenhouse Gases Emission

Bt(Bacillus thuringiensis) corn(Zea mays)(Bt corn) is one of the most rapid commercialization of genetically modified crops in the world. The commercial cultivation and application of crops expressing insecticidal proteins(Cry toxins) from Bt effectively control target pest and reduce the use of chemical pesticides. However, there are more and more ecological risks and environment problems. Bt protein released by Bt crops can enter the soil through Bt crops straw returning to field, which may affect soil ecosystem. In this paper, two transgenic Bt corns(5422Bt1, 5422CBCL) expressing Cry1 Ab and their near-isoline(5422) were used to study on the influence of Bt corn straw returning(straw mulching, soil straw mixing) and Eisenia fetida activity on Bt protein degradation, soil greenhouse gases emission, nutrient content and the amount of genes related to N cycle.The main results were as follows:1. Cry1 Ab protein content in the Bt corn straws significantly decreased with the test time. It discomposed more than 80% after 15 days in two kinds of Bt straw. The degradation of Cry1 Ab protein in 5422Bt1 corn straw with earthworm was faster than that in the treatment without earthworm. Whether the treatments with earthworms or not, the degradation of Cry1 Ab protein in soil from straw mulching treatments was faster than that from soil-straw mixture treatments. Cry1 Ab protein content in earthworms from straw mulching treatments was significantly higher than that from soil-straw mixture treatments. However, no matter what kind of straw returning, there was no significant difference in the Cry1 Ab protein in the earthworm between 5422Bt1 and 5422 CBCL.2. Bt corn straw returning had no significant effect on cumulative N2 O emissions in earthworm treatments. The addition of earthworms reduced the period of N2 O emissions fluctuation, greatly improved cumulative N2 O emissions. Soil cumulative N2 O emissions in mulching treatment were greater than that from soil-straw mixture treatments. Bt corn strawreturning had no significant effects on cumulative CO2 emissions in non-earthworm treatments. Cumulative CO2 emissions in the 5422Bt1 treatment was significantly higher than that of 5422 and 5422 CBCL treatments from soil-straw mixture with earthworms treatments. Soil cumulative CO2 emissions from straw mulching treatments were greater than that from soil-straw mixture treatments.3. Corn varieties had significant effect on the number of amo A and nir S genes not nir K gene. Earthworm treatment significantly improved the copy numbers of amo A and nir K genes in soil after 90 days. In 5422 and 5422Bt1 straw mulching treatments, the addition of earthworms reduced the copy numbers of nir S gene significantly. The copy numbers of nir S gene decreased in soil over time. The copy numbers of nir K gene increased in straw mulching treatments but decreased in soil-straw mixture treatments with time. The returning way had no significant effects on the number of amo A, nir S and nir K genes.4. The levels of available potassium in 5422Bt1 treatments were significantly higher than that in 5422 and 5422 CBCL treatments. The content of soil nutrients in soil-straw mixture treatment was higher than that in straw mulching treatments. Earthworms had significant effects on the content of nitrate nitrogen in soil.Therefore, Bt corn straw returning had no significant effects on cumulative N2 O with earthworms and CO2 emission without earthworms, whereas Bt corn straw returning presented significant effects on the content of organic matter and available potassium, the copy numbers of amo A and nir S genes in soil. Earthworms could promote the degradation of Cry1 Ab protein and increase cumulative N2 O emissions in soil, which may be related to the soil environment(the copy numbers of the denitrification genes and the soil nutrient content). Cry1 Ab content, cumulative N2 O and CO2 emissions in straw mulching treatments were higher than that in soil-straw mixture treatments. The copy numbers of amo A, nir S and nir K genes were greater in soil-straw mixture treatments.