| With rich plant protein and fat,soybean is an important oil crop,which is widely planted.In recent years,to increase the soybean production and improve the oil content of the soybean,a series of transgenic soybeans have been cultivated by using genetic engineering methods and are widely planted.Since transgenic soybeans are crops containing resistance genes,the long-term accumulation of their litterfall,exudates and residues in the soil changes the microbial community in the soil structure layer.Therefore,studies on the effects of BADH-transgenic soybean on soil bacterial community structure as well as soil physical and chemical proprieties are of research application value for regulating soil ecological environment.Betaine is synthesized by betaine aldehyde dehydrogenase(BADH)and choline monooxygenase(CMO)in plants through catalysis.It's hard to determine the CMO's activity,thus BADH genes have become the significant object in the study of betaine gene.Scientists isolated and purified BADH genes in spinach successfully in 1981,which lays an important foundation for the birth of salt-tolerant new species.At present,most of the studies on BADH genes are focused on plants such as spinach and there are few reports on BADH-transgenic soybean studies.Taking the alkali-tolerant BADH-transgenic soybean(SRTS)and its receptor soybean(HN-35),a kind of non-GM soybean,as research materials,and combining field experiments with port experiments,this study adopts methods of PCR high-throughput to study effects of related functional bacterial communities in the rhizospheric soil.This study discloses the effects of the alkali-tolerant BADH-transgenic soybean on the bacterial diversity in the soil during the whole growth process,and the changes of soil physical and chemical properties along with the growth of the SRTS,providing theoretical references to evaluation standards on the soil microbial environment and effects of the root exudates of BADH-transgenic soybean.During the whole growth stages,the changing trend of pH and H+secretory amount in root exudates are consistent with that of its receptor soybean(HN-35),but the pH and H+secretory amount of the BADH-transgenic soybean are always higher than that of its receptor soybean(HN-35),which shows that BADH-transgenic soybean has a stronger ability to generate and release H~+.This study determines 7 kinds of low-molecular-weight organic acids in BADH-transgenic soybean and its receptor soybean(HN-35)in its root exudates.During the whole growth stages,BADH-transgenic soybean is significantly different in the organic acid types and content in its root exudates and the total content of organic acid is higher than that of its receptor soybean(HN-35).The organic acid excreted by BADH-transgenic soybean can provide the acidic environment for the growth of soil microorganisms,tolerating the alkali environment effectively.This study determines 13kinds of amino acids in BADH-transgenic soybean and its receptor(HN-35)in its root exudates,in which the organic acid types show no significant differences but the organic acid content is significantly different.Moreover,total content of amino acid in BADH-transgenic soybean is significantly higher than its receptor soybean(HN-35).Planting BADH-transgenic soybean can improve the formation of soil aggregate and contribute to increasing the moisture and fertility of soil.Total content of carbohydrates and content of various carbohydrates are notably different in the root exudates at the same growth stage between BADH-transgenic soybean and its receptor soybean(HN-35),in which total content of carbohydrates in BADH-transgenic soybean is higher than its receptor soybean(HN-35)respectively.Therefore,BADH-transgenic soybean planted in the saline alkali soil is with stronger vital power.Bacterial diversity of the BADH-transgenic soybean at different growth stages changes a lot,and the sequence coverage obtained during sequencing is relatively high.At the 97%identity,the microorganism sequence coverages of the samples at the seedling,flowering,podding,pod-filling and maturity stages are basically over 70%.At the 95%identity,the coverages reach about 70%.Shannon index of rhizospheric soil bacteria of the BADH-transgenic soybean at the seedling,flowering and maturity stages are significantly higher than that at podding and pod-filling stages.The bacteria types and abundance in the rhizospheric soil of the BADH-transgenic soybean are on a downward and then an upward trend during the whole growth stages.At the seedling and flowering stages,bacteria of the BADH-transgenic soybean in the rhizospheric soil are higher than that of its receptor soybean(HN-35)and bacteria types produced at the podding stages are lower than that of its receptor soybean(HN-35).Maximum number of common species of BADH-transgenic soybean and its receptor soybean(HN-35)at the seedling stage is 957,which greatly declines to 686 at the flowering stage.Minimum number of common species of BADH-transgenic soybean and its receptor soybean(HN-35)at the pod-filling stage is 621,which increases to 779 at the maturity stage.Diversity,structural composition and abundance of the common species of bacterial community in rhizospheric soil of BADH-transgenic soybean and its receptor soybean(HN-35)are the important evidences reflecting whether root exudates of crops with exogenous gene affects the microorganisms in the surrounding soil environment.Meanwhile they can influence and even change the absorption,utilization channel and efficiency of the nutrient substances in the soil for the crops.The moisture,exchangeable sodium,anion exchange capacity in rhizosphere soil for the BADH-transgenic soybean and maternal soybean are in the same changing trend during the whole growth stages,but total content in the BADH-transgenic soybean is obviously more than its receptor soybean(HN-35).Changes of these factors improves the rhizospheric environment of the plants efficiently.At the podding stage,soil microbial biomass nitrogen in the BADH-transgenic soybean is 4.7 times higher than that of its receptor soybean(HN-35).Biological nitrogen is of significance for regulating nitrogen cycle and transformation,which contributes to high quality of BADH-transgenic soybean in the saline-alkali soil.Soil microbial biomass phosphorus in the BADH-transgenic soybean gradually becomes higher than that of its receptor soybean(HN-35)at the podding stage.The number of organic phosphorus bacteria and inorganic phosphorus bacteria is of great significance for promoting transformation of organic phosphorus in the soil and coordination of absorbed phosphorus for crops.Above all,changes of the soil physical and chemical properties cause the ecologically functional changes of rhizospheric soil microscopically and shows the improvement of adversity-tolerant growth,quality and output macroscopically.However,this study tests 8 indexes for the soil physical and chemical properties.At the maturity stage,biomass carbon and biomass phosphorous,2 of the indexes,in the BADH-transgenic soybean is significantly higher than that of its receptor soybean(HN-35).Exchangeable sodium,anion exchange capacity,total alkalinity,and biomass nitrogen,4indexes of them,in the receptor soybean(HN-35)are a little higher than that of BADH-transgenic soybean.Available phosphorus,one of the indexes,in the receptor soybean(HN-35)is significantly higher than that of BADH-transgenic soybean. |
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