The Analysis Of Underground Microbial Community In Salt-tolerant Jerusalem Artichoke And The Mechanism Of Endogenous Nitrogen-fixing Stenotrophomonas To Promote This Growth Under Different Nitrogen Treatments

China has a large number of coastal resources,and the coastal beach is one of its important geomorphic forms.However,the salinization of the beach is getting worse.The effective development and utilization of this part of the beach resources has received people's attention.Jerusalem artichoke(Helianthus tuberosus),as an agricultural crop,has the characteristics of strong adaptability,barren resistance,saline-alkali resistance,drought resistance,etc.,and has been widely planted on shoal saline-alkali land.In the traditional planting process of Jerusalem artichoke,fertilization and regular topdressing are needed.Nitrogen fertilizer is one of the essential fertilizers,but the use of fertilizer will bring many environmental problems.Now,some endophytic nitrogen fixing bacteria can provide nutrients for plants through biological nitrogen fixation,secretion of growth hormone and other mechanisms to promote the growth and development of plants.This kind of biological fertilizer has been widely used in forestry,agriculture and other fields.Therefore,if we can find biological bacterial fertilizer that plants can effectively use to replace nitrogen fertilizer or reduce the use of nitrogen fertilizer,this will be of great significance to the sustainable development of agricultural economy.In order to explore the application of nitrogen fertilizer on the microbial community changes in the lower part of Jerusalem artichoke,this article analyzed the microbial community changes in the lower part of Jerusalem artichoke by high-throughput sequencing and bioinformatics.An endophytic nitrogen-fixing bacterium with good growth-promoting characteristics was obtained from the tuber plant Jerusalem artichoke tuber,and its colonization in Jerusalem artichoke and its plant-promoting effect were investigated in depth.The main research contents are as follows:1.Every two months,16S and ITS high-throughput sequencing were carried out on the underground part of Jerusalem artichoke under two fertilization treatments(P and K application and N,P and K application),and the results were analyzed by bioinformatics.The results showed that there were differences in microbial community changes between bacteria and fungi.From the perspective of species composition,under the level of class,the dominant class of bacteria and fungi had little effect between different treatments.At the genus level,the application of nitrogen fertilizer had little effect on the main dominant genus of Jerusalem artichoke.The proportion of Acinetobacter and Pseudomonas accounted for the majority of the year.The application of nitrogen fertilizer had a greater influence on the composition of the dominant genera of fungi,and the species changed significantly after the application of nitrogen fertilizer and there was no absolute dominant genera.From the perspective of network topology,the effect of nitrogen application on bacteria and fungi was also the opposite.The number of OTUs with relatively high abundance in the treatment of nitrogen application was significantly higher than that in the case of no nitrogen application,and the negative correlation between OTUs was also significantly increased.However,the network structure of fungi was that the number of OTUs was more and the negative correlation was more when nitrogen was not applied.From the point of view of species diversity,there are some differences between the bacterial Chao1 index and Shannon index under the two fertilizer treatments.In May and September,the bacterial diversity was the highest,and from the NMDS analysis,we can see that there were significant differences in community structure between different time periods,and the application of nitrogen fertilizer had a significant impact on community structure.The alpha diversity of fungi was higher in July and September,and the application of nitrogen had no significant effect on community structure.2.21 endophytic nitrogenfixing bacteria were isolated from the underground part of Jerusalem artichoke.The activity of nitrogen fixing enzyme was determined by acetylene reduction method,among which Stenotrophlomonas sp.SI-NJAU-1 with the highest activity was 36.98 nmol/(h·ml).The strain also has high IAA secretion and inorganic phosphorus activation characteristics,and the nifH gene was confirmed by PCR.The green fluorescent protein-labeled strain SI-NJAU-1 y was used to colonize different Jerusalem artichoke tubers.The strain was found to be motile and distributed in the roots and leaves as the plant grew.Through the greenhouse experiment,we found that SI-NJAU-1 had a significant growth promoting effect on Jerusalem artichoke without nitrogen or low nitrogen.After 40 days,the biomass and nitrogen related indexes of the experimental group were significantly higher than those of the control group.Compared with the control group,Jerusalem artichoke biomass was 7g heavier,total nitrogen content was 9.96g/kg higher,protein concentration was 135.33 g/ml higher,nitrate reductase content was 1.8U/g higher,and glutamine reductase content was 3U/g higher.However,under low and medium nitrogen nutrition levels,although some physiological indicators have changed,most of them have no obvious overall changes.