Effects Of Simulated Nitrogen Deposition On Early Regeneration Of Haloxylon Ammodendron Seedlings And Transcriptomics

Due to the impact of global climate change and human activities,the vegetation degradation in arid desert areas is becoming more and more serious,and the ecosystem has also been seriously damaged.The increasing salinization of soil and the lack of soil nutrient content are two key factors limiting the successful regeneration of pike seedlings during snowmelt.Haloxylon ammodendron,as a dominant species in desert area,has great ecological value for the protection and management of desert ecosystem.Therefore,in this study,to investigate the effects of nitrogen addition,salinity stress and their interaction on seed germination and seedling growth during snowmelt,we conducted indoor simulated germination tests and seedling growth pot experiments on H.ammodendron.The results of the study are as follows:(1)With the increase of nitrogen concentration,the germination rate and germination index of H.ammodendron seeds decreased gradually.With the increase of salt concentration,the germination rate,germination potential and germination index of H.ammodendron seeds decreased gradually.Under the interaction of stress,the addition of medium concentration of nitrogen(20～40 mmol/L)could significantly improve the germination rate of H.ammodendron seeds under medium and high concentration salt stress(>300 mmol/L).(2)With the increase of nitrogen concentration,the superoxide dismutase(SOD)activity and soluble protein content of H.ammodendron seedlings showed an overall trend of first increasing and then decreasing,and the highest value was at the nitrogen content of 80 mmol/L.while the peroxidase(POD)and catalase(Catalase,CAT)activities showed a downward trend.With the increase of salt concentration,SOD activity and soluble sugar content of seedlings decreased first and then increased,POD,CAT activity and malondialdehyde(MDA)content increased first and then decreased,while soluble protein content increased gradually;Under the interaction of different concentrations of nitrogen addition and salt stress,the POD,CAT activities and MDA content of H.ammodendron seedlings were significantly increased compared with high concentrations of salt stress(600～700 mmol/L).(3)When the salt stress concentration was 500 mmol/L,the plant height of H.ammodendron seedlings decreased gradually with the increase of nitrogen addition.When the salt stress concentration was 700mmol/L,with the gradual increase of nitrogen addition,the root length of H.ammodendron seedlings increased gradually and was significantly higher than that of the control.When the salt stress concentration was 700 mmol/L,the aboveground dry weight,underground dry weight and total biomass of H.ammodendron seedlings were lower than those under the salt stress concentration of 500 mmol/L.The aboveground dry weight of seedlings increased.(4)A total of 453144052 Transcripts and 123324994 Unigenes were obtained by transcriptome sequencing.In the salt stress concentration group of 500 mmol/L,the high nitrogen group(80 mmol/L)up-regulated and down-regulated the most genes;in the salt stress concentration of 700 mmol/L,the medium nitrogen group(40 mmol/L)up-regulated and down-regulated genes most.Among all differential genes,a total of 1529 transcription factor genes from 88 families were found,mainly C3 H,WRKY,B3,AP2,MYB and C2H2 families.The significantly enriched differential genes of GO function were mainly related to oxidoreductase activity,hydrolase activity and carbohydrate metabolism process.The pathways significantly enriched by KEGG were mainly involved in phenylpropane biosynthesis,RNA polymerase,plant hormone signal transduction,nitrogen metabolism and photosynthesis.To sum up,for the regeneration of H.ammodendron seedlings during the early spring snowmelt period,the addition of nitrogen can alleviate the effect of salt on seed germination to a certain extent,improve the activity of stress-resistant enzymes,and improve the plant height and root length of seedlings,which is related to the The regulation of transcription factor genes,nitrogen metabolism pathways and photosynthesis in some families are inextricably linked.