Effects Of Bacilus Thuringiensis(Bt)Rice Straw Return On Earthworms Eisenia Fetida

Rice straw return to soil can be used as matrix to raise earthworms,which not only reduce the environment pollution caused by straw burning in the field,metabolic products of earthworms but also provide nutrients for the growth of plants.This is an effective way to realize the agricultural mode of circulation.Bacilus thuringiensis(Bt)toxin from transgenic rice can enter the soil through different ways,including pollen deposition,root exudation,plant residues after the harvest of Bt rice and rice straw return to soil,which presented potential effects on soil non-target amimals.Here,a laboratory experiment was conducted to evaluate the potential risks of Bt rice straw return on the non-target soil earthworms Eisenia fetida by feeding with the mixture of rice straw and soil(rice straw:soil=1:19).We evaluate the effects of Bt rice(F1,T775)and non-Bt rice(TYHZ)(regared as I group),Bt tianyou and Tianyou(II group),Bt shanyou63 and Shanyou63(III group),2018Bt and non-Bt rice Meixiangzhan2,Hanghui1179 and Hanghui38(IV gruop).The effects of Bt rice straw return on survival rate,relative growth rate(RGR)and reproduction of E.fetida were determined on day 7,15,30,45,60,75,90.The total protein,Superoxide dismutase(SOD),Glutathione peroxidase(GSH-PX)of E.fetida was also determined to investigate the influence of Bt rice straw return on earthworm physiology.The mechanism of impacts of Bt rice return on earthworm was revealed by detecting the contents of Bt protein in earthworms and mixture of rice straw and soil(substance)and the nutrients in the substances.The main results were as follows:1.Bt rice straw return had no effects on the survival of E.fetida.In addition to F1 and Bt shanyou63 inhibited the growth of earthworms in the short term(7-15),no difference of RGR was found between Bt and non-Bt treatments.The reproduction of earthoworms was inhibited in F1 and T775 treatments,whereas no adverse effect of earthworm reproduction was found in Bt tianyou,Btshanyou63 and 2018Bt treatments during the whole experimental period.2.Bt rice straw return had no effect on the contents of total protein in E.fetida.On the7^th d,the SOD activities in E.fetida increased in F1 treatments compared with TYHZ treatment and decreased in T775,Bt tianyou and Bt shanyou63 treatment compared with TYHZ,Tianyou and Shanyou63 treatments,respectively.The GSH-PX activity in E.fetida was higher in Bt treatmetns than non-Bt treatments in the short time(7-15 d)in I,II,and III group.Bt rice straw return had no impact on the SOD activity and GSH-PX activity in IV group.3.A certain amount of Bt proteins was detected in E.fetida after ingesting Bt rice straw,and there was no difference of Bt protein contents among different sampling times.The degradation of Bt proteins of all Bt rice treatments in the substances showed a rapid declined in 0-7 d and then stable at low concentration for a long time(15-90 d).The shift-log model fitted the decay pattern of the Bt protein in the substance,the results indicated that the DT₅₀ of Bt protein in with earthworms group were 0.64-1.29 d,the DT₉₀were 2.51-5.16 d.The DT₅₀ of Bt protein in no earthworm groups were 0.65-1.31 d and the DT₉₀were 2.57-5.27 d.The Bt protein was not acculumated in the substances in the long run.E.fetida activity accelerated the Bt protein degradation in the substance.4.There was no difference of organic matter(OM)and total potassium(TK)contents between Bt rice and non-Bt rice treatmetns in four groups.The contents of total phosphors(TP)was significantly lower in F1 and T775 treatments than TYHZ treatments,where as the contents of available phosphors(AP)was higher than TYHZ treatments;In II group,the contents of TN,TP and available nitrogen(AN)were significantly higher in Bt tianyou treatments than tianyou treatments.In III group,the contents of TN,AN and avaliable potassium(AK)were significantly higher in Bt shanyou63 treatments compared with shanyou63 treatments.The contetns of AP in 2018Bt+E,2018Bt,AK in Meixiangzhan2+E,Meixiangzhan2 treatments were the lowest compared with other treatments in IV group.E.fetida decreased the contents of OM,and increased the contents of AP and AN in the substances.5.GSH-PX can reflect the changes in growth of E.fetida when Bt rice straw return to the field,namely higher GSH-PX,lower growth.The contents of OM,Bt protein,AN and AK in the substances have significant impacts on the life parameters and physiology and biochemistry of earthworms.The effect of Bt protein on the growth of earthworms was positive.And the changes in AK,AN and OM have a strong influence on the SOD and GSH-PX activities.In conclusion,Bt rice straw return had no adverse effects on the survival of earthworms.The growth of E.fetida was inhibited in F1 and Bt shanyou63 treatments on7-15^th d,and the reproduction of E.fetida was inhibited in F1 and T775 treatments,whereas Bt rice straw return have no effects on growth and reproduction of earthworms.The changes in SOD activities and GSH-PX activities were not caused directly by Bt protein released from Bt rice straw.The characteristics of rice straw,and the susbstance nutrients were the main factor influencing the physiology and biochemistry of of earthworms.The presence of earthworm accelerated the decay of Bt proteins in the substances,decreased the contents of OM,and increased the contents of AP and AN in the substances.