Transgenic Insect-resistant Cotton's Influence On Rhizosphere Soil Microorganisms And Its Environmental Effect

Cotton,as the transgenic crop with the biggest planting area,its potential risk towards the environment is eliciting more and more attention.There already exists experimental results which proves that the transgenic insect-resistant cotton has different degrees of influence on non-target pests and natural enemies.But its other influence on the ecosystem has not yet been final concluded.The soil ecosystem is the place where the crops conduct material and energy cycle.Currently,the problems that whether transgenic crops have influence on the soil ecosystem and if so,what kind of influence it is are still under investigation.This research adopted the second-generation high-throughput sequencing method,the method of enzyme-linked immunoassay and etc to study the four kinds of promoted transgenic insect-resistant cotton in Shandong Province in 2016 and to probe into its influence on rhizosphere soil microorganisms,residual quantity of BT toxin protein and concentration of available nutrient.This research aims at providing the evaluation of transgenic insect-resistant cotton's potential risks to the soil ecosystem with scientific evidences and facilitating the sound development of the biosafety management of our country.Chief results of the research are as follows:(1)Generally speaking,there was no significant difference between the influence on the rhizosphere soil microorganisms imposed by the common cotton in the control group and by the transgenic insect-resistant cotton.As for the few strains of which the influence on microorganisms is different from that of the control group,the extent of the influence varies from variety to variety.From the aspect of growth period,during seeding stage and bud stage,the difference of influence was not significant.And during flowering and boll setting stage,the species richness of flora declined dramatically.When it came to boll opening period,the richness rose markedly.But there also existed a minority of strains that went against the general trend of the soil microorganisms.For example,the amount of bacteroidetes during seeding stage,bud stage and flowering and boll setting stage was significantly higher than that during boll opening stage.And as for strptomyces,the situation was just the opposite.(2)The concentration of Bt toxin protein in transgenic insect-resistant cotton's rhizosphere soil increased before decreasing within a whole growth period.The maximum concentration was reached at bud stage,and the minimum concentration was at boll opening stage.At every stage within a\the growth period,The concentration of Bt toxin protein in transgenic insect-resistant cotton's rhizosphere soil was significantly higher than that in common cotton's rhizosphere soil.(p<0.05)(3)The concentration of nitrate nitrogen in transgenic insect-resistant cotton's rhizosphere soil saw a downward trend throughout the growth period.Within it,during seeding stage and bud stage,the concentration of nitrate nitrogen in each four varieties of transgenic insect-resistant cotton's rhizosphere soil was below that in common cotton's rhizosphere soil.And during flowering and boll-setting stage,the concentration of nitrate nitrogen in rhizosphere soil varied from variety to variety.During boll opening stage,the difference of concentration between common and transgenic cotton was not significant.(p>0.05)The concentration of ammonium nitrogen in transgenic insect-resistant cotton's rhizosphere soil saw a downward trend throughout the growth period.Within it,during seeding stage,the concentration of ammonium nitrogen in each one of the four varieties of transgenic insect-resistant cotton's rhizosphere soil was not significantly different from that in common cotton's(P>0.05).During bud stage and flowering and boll-setting stage,the concentration in transgenic insect-resistant cotton's rhizosphere soil was markedly lower than that in common cotton's(P<0.05).During boll opening stage,only the concentration in the transgenic cotton named Xinqiu No.4's rhizosphere soil was notably higher than that in common cotton's(P<0.05).the concentration in each of other varieties of transgenic cottons' rhizosphere soil was not significantly different from that in common cotton's(P>0.05).The concentration of available phosphorus in transgenic insect-resistant cotton's rhizosphere soil was on the rise throughout the growth period.Within it,only the concentrations in the rhizosphere soil of the studied cotton No.28 and No.36 during bud stage and boll opening stage were significantly higher than the concentration in common cotton's rhizosphere soil(P<0.05).The concentration in other varieties' rhizosphere soil during other growth periods was not significantly different from that in common cotton's(P>0.05).Generally speaking,from what this article has mentioned above,we can reach the conclusion that transgenic insect-resistant cotton's influence on rhizosphere soil microorganisms was insignificant and the influence on the minority microorganism species would only be imposed by certain varieties,at a certain stage and it has not lasted throughout a whole growth period.It was the growth period that acted as the chief factor which led to the variation of rhizosphere soil microorganisms,the variety of cotton came second in that aspect.The concentrations of BT toxin protein,nitrate nitrogen,ammonium nitrogen and available phosphorus in cotton's rhizosphere soil were mainly affected by the periods of growth and the plantation of transgenic insect-resistant cotton.Besides,the variety of cotton was also a crucial factor of the influence.