| In recent years,the climate change have brought huge losses in agriculture production,it has been a widely focus attention and become global environmental problems in the world.The latest data showed that the concentration of global CO2 has incerased from 280 ppm before the industrial revolution to 406 ppm in 2017,and global temperature have gradually warmed since the industrial revolution.The global average temperature between 1990 and 2005 has increased by 0.15?-0.3? per decade,and the global climate will continue to warm in the future.As global climate change issues become more prominent,Bt crops will face more ecological risks.Many studies have showed that elevated CO2 not only affect the proportion of chemical components and nutrients in plants,such as increase the carbon nitrogen ratio,yield and biomass of crops,simultaneously,significantly reduce nitrogen content and expression of Bt toxin protein in transgenic Bt cotton and Bt rice.It has been shown that a new ecological risk of reducing target-insect resistance due to the"Dilutioneffeet" of Bt toxin protein and "Silence" in the Bt gene expression.Some studies have pointed out that the physiological levels of nitrogen metabolism in transgenic Bt crops can affect the expression of Bt toxin protein,so the optimal management of N fertilizer can improve the nitrate reductase and enzyme activity of nitrogen metabolism in Bt crops to promoting the expression of Bt toxin protein.How do Bt crops respond to their target lepidopteran pests under the elevated atmospheric CO2 and temperature?What are the differences in fertilizer efficiency and insect resistance expression of maize infected by different azotobacter?The solution of these problems can give us a new biological regulator with azotobacters to optimize N fertilizers to enhance the target-insect resistance of Bt crops,and ensure the safe production and ecologically sustainable use of Bt crops in China under climate change.This study was closely related to the actual production of major food crops(Bt maize as the research object)infected by different azotobacter in China and combined with the elevated atmospheric CO2 and temperature.It focused on the effects of elevated CO2 and temperature on development and target-insect resistance of transgenic crylIe maize infected by Azospirillum brasilense and Azotobacter chroococcum,Main results were as follows:1.Assessment of elevated CO2 and temperature on development and yield oftransgenic crylle maize infected by azotobacter.In this study,Bt maize infected by different azotobacter was used as the research object,combined with elevated atmospheric CO2 and temperature,and the development,yield,plant nutrition and soil fertility of Bt maize compared with its parental lines were studied.The test results showed that the double-ambient CO2 significantly increased the stem diameter,plant height,root shoot ratio,plant dry weight,and yield indexs(100-grain weight and grain dry weight per plant);the infection with Azospirillum brasilense(AB)and Azotobacter chroococcum(AC)both significantly increased the stem diameter,plant height,root shoot ratio,plant dry weight,and yield indexs(100-grain weight and grain dry weight per plant),It indicated that the double-ambient CO2 and azotobacter treatments both significantly increased the biomass accumulation and growth of maize.The double-ambient CO2 significantly increased the total carbon content and a few essential amino acids(such as threonine,lysine,histidine and arginine)and reduced the total nitrogen content of maize,total phosphorus content,total potassium content and some amino acids(aspartate,serine,glutamic acid,glycine,alanine,cysteine and tyrosine);Infection by AB and AC significantly increased the total nitrogen content and total phosphorus content and most amino acids(aspartate,threonine,glutamic acid,glycine,alanine,cysteine,tyrosine,lysine,and histidine),simultaneously,the total carbon content,total potassium content and a few amino acids(serine and arginine)were reduced.It indicated that the double-ambient CO2 was beneficial to the utilization and accumulation of carbon in maize and reduced the nutrition level of maize.It alleviated the adverse effects of double-ambient CO2 on nutrient utilization of maize and enhance plant nitrogen utilization and nutrient levels by azotobacter treatments.Infection by azotobacter was beneficial to optimize N fertilizers to enhance the yield in China under climate change.2.Effects of elevated CO2 and temperature on the expression of protective enzymes and Bt toxin protein of transgenic crylle maize infected by azotobacter.The increase of atmospheric carbon dioxide concentration and the concomitant global warming have attracted worldwide attention as two major factors of climate change and have become "global hot topics".In this study,Bt maize and its parent lines were taken as the research object,combined with two major environmental factors and azotobacter treatment,the differences in the expression of self-protective enzymes and Bt toxin protein in transgenic Bt maize in plants' physio-biochemistry was described and compared.The experimental results showed that the double-ambient CO2 significantly increased the activity of the plants' protective enzyme and the five amino acids content(proline,methionine,isoleucine,leucine,phenylalanine)closely related to the secondary defense(JA);Infection by two azotobacter also significantly increased the activity of the plants'protective enzyme and the contents of five amino acids.It indicated that environmental pressure promotes the plants' defense system,and infection by azotobacter achieves complementary effects and promotes the plants' induced resistance.The results of ELISA and Western experiments showed that the double-ambient CO2 significantly reduced the expression of Bt toxin protein in transgenic Bt maize,and infection by AB and AC were significantly beneficial to expression of Bt toxin protein in transgenic Bt maize.The results showed that double-ambient CO2 inhibited the expression of Bt toxic protein in transgenic Bt maize,and we had mitigated these adverse effects through azotobacter infection.Infection by azotobacter was beneficial to optimize N fertilizers to reduce the ecological risk of decreasing target-insect resistance,simultaneously,promote the the expression of Bt toxic protein and maize self-defense system in China under climate change.3.Influence of elevated CO2 and temperature on development and food utilization of target armyworm Mythimna separata fed on transgenic cry1Ie maize infected by azotobacter.In this study,the influence of elevated CO2 and temperature on development and food utilization of target armyworm Mythimna separate(Lepidoptera:Noctuidae)fed on transgenic crylle maize infected by azotobacter were studied.The results showed that the double-ambient CO2 significantly increased the larval duration,pupal duration,relative consumption rate(RCR)and approximate digestibility AD of armyworm larvae;The pupation rate,pupal weight,adult longevity and fecundity,relative growth rate RGR,efficiency of conversion of digested food ECD and efficiency of conversion of ingested food ECI.It was shown that double-ambient CO2 had a negative effect on the development and food utilization of herbivorous pests by reducing the nutrient levels of host plants.Target armyworm increased their feed intake to meet their growth to respond against the negative impact.Predicting the risk of of M Separata will be worse in maize field under future climate change;Transgenic Bt maize infected by azotobacter significantly increased the larval duration,pupal duration,RCR and AD,shortened adult longevity,while significantly reduced pupation rate,pupal weight,adult fecundity,RGR,ECD and ECI,and there was a opposite effect in its parent lines.It indicated that the infection by azotobacter increased the expression of Bt toxins protein in transgenic Bt maize,and the development and food utilization of the target armyworm were hindered or even lethal.Considering comprehensively,elevated CO2 will lead to increase feeding intake of armyworm to aggravate field hazards,simultaneously,there is a "Dilutioneffeet" of Bt toxic protein under elevated CO2.Application of rhizosphere azotobacter will help alleviate this phenomenon and enhance the target-insect resistance of Bt maize.As expected,there were no significant interannual changes in the field data of two consecutive years,and the temperature factor had no significant effect.From the overall trend,we can see that the double-ambient CO2 reduces the nutrient level of maize,inhibits the expression of Bt toxin proteins in transgenic Bt maize,and indirectly leads to the increase of M separata with increasing crop intake.The application of azotobacter provides a new biological regulator to relieve the environment pressure.This study systematically clarified the growth and target-insect resistance of Bt maize infected by azotobacter under climate change(CO2,temperature)and validated them from insect physiology,plant nutrition and bio-physiology,simultaneously,clarified the occurrence of target armyworm M.separate in future and provided a new biological regulator with azotobacters optimize N fertilizers to enhance the target-insect resistance and yield of Bt crops,and ensure the safe production and ecologically sustainable use of Bt crops in China under the future climate change. |
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