Response To The Growth Physiology And PAL In Populus Simonii × P.nigra Under Nitrogen Treatment

Nitrogen is the basic element of important components in plants and one of the main limiting factors at ecosystem productivity,nitrogen can promote the growth of trees and help forests increase yield.it is of great theoretical and practical significance to study the effects of nitrogen on forest growth.Lignin content is one of the important indicators to measure the wood characteristics,and studies have shown that under certain conditions,the poplar lignin content gradually decreases with the increase of nitrogen concentration.PAL is a key enzyme and rate-limiting enzyme in the first step of the lignin biosynthesis pathway,which is essential for the synthesis of lignin.This study takes Populus simonii × P.nigra as the research object,three kinds of nitrogen fertilizer(NH4Cl,NaNO3 and NH4NO3)with concentration gradients of 0.1 mmol·L-1,2 mmol·L-1 and 10 mmol·L-1 were used to culture Populus simonii × P.nigra,based on the study of the effects of nitrogen on the growth and physiology of Populus simonii × P.nigra,whether the change in lignin content is also involved in the PAL gene,further understand the response of the PAL gene to nitrogen,and analyze whether there is a relationship between nitrogen,PAL and lignin.We have performed the following related experiments with the following results:(1)In order to understand the basic characteristics,structure,and evolutionary characteristics of PAL gene in poplar,the bioinformatics method was used to analyze the characteristics of PAL gene in the gene database of Populus trichocarpa,as a reference basis for the study of PAL gene in Populus simonii×P.nigra.The physical and chemical properties of the five proteins are similar,all the genes except PtrPAL4 and PtrPAL5 are on chromosome 10,PtrPAL1,PtrPAL2,and PtrPAL3 are on chromosomes 6,8,and 16.The five proteins are mainly distributed in the chloroplast,and the tertiary structure is consistent,all are homotetramers,and the results of evolutionary relationship show that the PAL gene of poplar is highly homologous to Oryza sativa and Arabidopsis thaliana.(2)In order to study the effect of different forms of nitrogen on the growth phenotype of Populus simonii × P.nigra at high and low concentrations,three kinds of nitrogen,NH4Cl,NaNO3 and NH4NO3 were selected,and different concentrations(0.1 mmol·L-1,2 mmol·L-1,10 mmol·L-1)were set.After 18 days,under the condition of 0.1 mmol·L-1,the measured values of plant height,ground stem,dry weight,fresh weight and leaf area were significantly reduced(p<0.05),it increased significantly under the condition of 10 mmol·L-1 high nitrogen(p<0.05),the comparison of three forms of nitrogen showed that the plant height,ground diameter,fresh weight,dry weight and leaf area under the treatment of NaNO3 were significantly higher than those under the other two nitrogen treatments(p<0.05).(3)In order to further understand its growth physiology,the contents of total nitrogen and carbon in roots,stems and leaves,photosynthetic parameters and chlorophyll were measured.The results showed that with the increase of nitrogen concentration,the carbon and nitrogen content of Populus simonii × P.nigra increased,when the nitrogen concentration was 10 mmol·L-1,the chlorophyll content and photosynthesis were significantly higher than other concentrations(p<0.05),the physiological indexes of NaN03 treatment were significantly higher than those of the other two nitrogens(p<0.05);(4)In order to further understand the changes of wood properties,the xylem area and lignin content were measured.The results showed that the xylem area under 0.1 mmol·L-1 nitrogen treatment was significantly lower than that under normal nitrogen treatment(p<0.05),the xylem area of 10 mmol·L-1 was significantly higher than that of other treatments(p<0.05);Under the same concentration of nitrogen treatment,the area of NaNO3 treatment was significantly higher than that of other forms of nitrogen treatment(p<0.05).With the increase of nitrogen concentration,the content of lignin decreased significantly(p<0.05),the results showed that under the same nitrogen concentration,the lignin content of NaNO3 treatment was significantly lower than that of other treatments(p<0.05);(5)In order to understand whether nitrogen affects PAL during the change of wood quality,measured PAL activity and expression level under nitrogen treatment.The results showed that the PAL activity of 0.1 mmol·L-1 was significantly higher than that of other treatments(p<0.05),indicating that low nitrogen can effectively promote the enhancement of PAL activity,at the same concentration,the PAL activity of NaNO3 treatment was significantly higher than that of the other two forms(p<0.05).At the same time,the expression levels of 5 genes in PAL showed that 0.1 mmol·L-1 nitrogen treatment could induce PAL gene expression,however,when the nitrogen concentration was 10 mmol·L-1,the expression of PAL gene was inhibited,and the expression of PAL gene was reduced under high nitrogen treatment.The comparison of different forms of nitrogen showed that,when the nitrogen concentration was 0.1 mmol·L-1,the expression of PAL2,PAL4 and PAL5 in the treatment of NaNO3 and NH4NO3 was lower than that in the treatment of NH4Cl,when the nitrogen concentration was 10 mmol·L-1,the expression of PALI was inhibited most obviously under the treatment of NaNO3,this shows that the nitrogen concentration can affect the expression of PAL gene,and the form of nitrogen will also make a difference in expression.