Study On Abundance Characteristics Of Nitrogen Cycle Functional Genes In Tobacco-growing Soil

Tobacco is an economic crop that should not be cropped continuously.Long-term continuous cropping will lead to a decline in tobacco quality and yield.Soil micro-ecological imbalance is an important cause of continuous tobacco cropping obstacles.A variety of microorganisms participate in the nitrogen cycle that maintains the soil micro-ecology.Therefore,changes in the structure of the nitrogen cycle microbial community may lead to an imbalance of soil nitrogen cycle,thereby causing tobacco continuous cropping obstacles.From the perspective of the different abundance of nitrogen cycle microorganisms under different planting systems,this is the starting point to study the changing law of nitrogen cycle microorganisms in continuous cropping soil.In this study,the tobacco-planting soil in Luoning Township and Xiaojie Township tobacco areas in Luoning County was selected as the research object The tobacco-planting soil in Luoling Township was selected for continuous tobacco cultivation for more than five years,and the tobacco-growing soil in Xiaojie Township was continuously cultivated for more than five years,and the tobacco-planting soil in Xiaojie Township where tobacco was grown for only one year,and the three samples were labeled as LN1,LN5,and LN10,respectively.The metagenomic sequencing technology was used to compare with the nitrogen cycle functional gene database NCycDB and the species annotation NR database.The results are as follows:1.The relative abundances of ammonia oxidizing archaeal genes amoA_A,amoB_A,amoC_A,bacterial ammonia monooxygenase genes amoB_B and amoC_B involved in the nitrification process are significantly different in LN1,LN5 and LN10.The genes amoA_A,amoB_A,amoB_B,amoC_B and the hydroxylamine dehydrogenase gene hao are all relatively abundant in LN10.Among the genes involved in the denitrification process in the reduction of dissimilar nitrate,the gene encoding nitrate reductase,narZ,has the lowest abundance in LN10,and the abundance of the nitrate reducing gene narY in LN1 is 1.12 times that of LN10,indicating continuous cropping soil The abundance of genes encoding nitrate reductase is higher,and the reduction of nitric acid to nitrous acid is carried out to a greater extent,which increases the risk of nitrogen fertilizer loss.The gene nirA,which is involved in the reduction of assimilated nitrate,which encodes iron redox protease,is relatively abundant in LN10,and the nitrate reduction gene nirD,which is involved in the reduction of dissimilated nitrate to ammonium,is relatively abundant in LN10.The functional genes involved in the process of organic nitrogen metabolism are generally higher in the sample LN10.For example,the genes encoding urease ureA,ureB,and ureC,the gene nmo encoding nitrate monooxygenase,and the gene asnB encoding asparagine synthetase have relatively high relative abundance in LN10.2.At the genus classification level,the nitrogen cycling microorganisms of Nitrobacter,Nitrosarchaeum,Nitrosococcus,Nitrosopumilus and Nitrososphaera are abundant in LN10.The degree is significantly higher than that of LN1 and LN5.In the three samples,the abundance of the nitrogen cycle microorganism Nitrosospira in LN10 was significantly higher than that in LN1 and LN5.The abundance of Nitrospina in LN 10 was significantly higher than that in LN1,and the abundance in LN5 was significantly higher than that in LN10.The abundance of Nitrospira in LN10 was significantly higher than that in LN1,and the abundance in LN5 was significantly higher than that in LN10.Nitrosomonas had the highest abundance in LN5 samples,and Nitrolancea had the highest abundance in LN1.The relative abundances were all at the same level,and the differences were significant.3.There are 131 species at the level of species classification.Among the nitrogen cycle microorganisms,there are 3 species of ammonia oxidizing archaea AOA,91 species of ammonia oxidizing bacteria AOB,and 3 species of nitrite oxidizing archaea NOA.There are 34 species of nitrite-oxidizing bacteria NOB.The comparison of the relative abundance among samples shows that the relative abundance of AOA,AOB,NOA and NOB in LN 10 is significantly higher than that in LN1 and LN5.The ammonia oxidizing bacteria and nitrite oxidizing bacteria involved in the nitrification process have the highest relative abundance in LN10 under species level classification,indicating that the nitrification process is stronger.Compared within the same sample,the relative abundance of AOA in LN 1 is lower than that of AOB,the relative abundance of AOA in LN5 is higher than that of AOB,and the relative abundance of AOA in LN10 is higher than that of AOB.4.Using Metascape platform to analyze GO biological function and enrich the KEGG pathway to clarify its functional abundance.The results showed that the functional abundance of nitrification process and complete nitrification process in LN10 was higher than that of LN1 and LN5.The assimilation nitrate reduction process,the dissimilation nitrate reduction process to ammonium,and the denitrification process all have high functional abundance in LN1,low functional abundance in LN5,and middle functional abundance in LN10.The whole process of nitrifying bacteria has a higher affinity for ammonia,and synthesizes more biomass,which increases the level of microbial nitrogen supply in the soil,indicating that the complete nitrification process is higher in LN10,and its nitrification ability is stronger.