| Bt(Bacillus thuringiensis)corn(Zea mays)(Bt corn)is one of the most rapid commercialization of genetically modified crops in the world.Bt protein released by Bt crops can enter the soil through Bt crops straw returning,which may affect soil animals.In this paper,two transgenic Bt corns(5422Bt1,5422 C BCL)expressing Cry1 Ab and their near-isoline(5422)were used to study on the influence of Bt corn straw returning(straw mulching and ploughing)on thesurvival rate,growth and reproduction of E.fetida,Cry1 Ab protein degradation,soil greenhouse gases emission,nutrient content and the amount of genes related to nitrogen(N)cycle.The main results were as follows:1.Bt corn straw returning had no deleterious effects on t he survival rate,relative growth rate(RGR)and the number of juveniles of earthworms.Compared to 5422 treatments,Bt corn straw mulching presented inhibited effects on cocoon production,while significantly higher number of cocoon was observed in Bt corn straw ploughing treatments.The way of straw returning had a significant effect on the survival rate,RGR and reproduction of earthworms: on the 90 t h d,the survival rate,RGR of earthworms from straw ploughing treatments were significantly higher than those from mulching treatments;compared to mulching treatments,significantly higher number of cocoon was produced by earthworms in 5422 CBC L ploughing treatments on the 45 t h,75 th d,in 5422Bt1 ploughing treatments on the 45 t h,60 t h,and 90 t h d;on the 45 t h,60 t h,and 90 t h d,the number of juveniles from straw ploughing treatments were significa ntly higher than those from mulching treatments.2.Regardless of the straw returning ways,the sampling time had a significant effect on the content of Cry1 Ab protein released from Bt corns.They decreased rapidly in 15 d and changed slowly in medimum and later period.During the medimum and later period,the earthworm activity could accelerate the degradation of Cry1 Ab protein in Bt straw.The degradation of Cry1 Ab protein in Bt straw mulching treatments was significantly faster than that of ploughing treatments.During the period from 45 to 75 d,Cry1 Ab protein in earthworms from mulching treatments was significantly lower than that of the corresponding ploughing treatments.At the end of test(90 d),Cry1 Ab protein in Bt straw,soil and earthworm was detectable.3.Greenhouse gas emission flux in soil gradually stabilized along with the experiment time.N2 O flux from Bt corn treatments was significantly higher than that of non-Bt corn treatments in the initial stage and no significance differences between Bt and non-Bt treatments were found in N2 O and CO2 flux during the the period from 15 to 90 d.Earthworm activity could increase the CO2 flux as well as N2 Oflux in mulching treatments.Regardless of earthworm activity,no significant differences among three corn treatments were found in the cumulative CO2 emission and global warm potential(GWP)as well as the cumulative N2 O emission from mulching treatme nts.However,the cumulative N2 O emission from Bt straw ploughing treatments was significantly higher than that of 5422 treatments.For 5422Bt1 mulching treatments,earthworm activity significantly increased the cumulative N2 O emission.4.Compared to 5422 treatment,Bt straw mulching significantly increased the content of alkali-hydrolyzable N in soil.For ploughing treatments without earthworms,Bt straw returning significantly reduced the contents of total N,alkali-hydrolyzable N,while the content of ammonium N in 5422 CBC L treatments was significantly higher than that of 5422 treatments.In earthworm treatments,the content of organic matter in 5422 CBC L treated soil was significantly lower than that of 5422 treatments.Regardless of straw returning way,earthworm activity could significantly increase the content of soil organic matter,total N,P,alkali-hydrolyzable N.Furthermore,the content of available P in 5422Bt1 treated soil and the content of ammonium N in 5422 CBC L treated soil was significantly higher that of the corresponding non-earthworm treatments.5.Corn variety and straw returning way individually and interactively affected on the gene copies(GC)of amo A and nir S,but not nir K in soil.Regardless of earthworm activity,the GC of amo Aand nir Sin 5422 CBC L treated soil was significantly higher than that of 5422 treatments on the 30 t h d.The GC of nir S from ploughing treatments was significantly higher than that of the corresponding mulching treatments.Earthworm activity had no effects on the GC of three genes.In summary,the content of Cry1 Ab protein decreased significantly along with experiment time,and it was detectable in Bt straw,earthworm and soil at the end of test.Bt straw returning had no deleterious effects on the survival rate,relative growth rate(RGR)and the number of juveniles of earthworms.During the most of testing time,Bt straw returning could not increase the N2 O and CO2 flux and GWP,while Bt straw ploughing could significantly increase the cumulative N2 O emission.Bt straw returning had minor effects on soil nutrients and the GC of three genes related to N cycle,but did not have a certain regularity.Compared to corn variety,other treating factors and their interactions,such as the way of straw returning,sampling time and earthworm activity,had a greater influence on the content of Cry1 Ab protein,soil greenhouse gases emission,nutrients and the amount of three genes related to N cycle in soil. |
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