| Populus euphratica is the tertiary relic species,belonging to the genus Populus in Salicaceae,is the most primitive desert riparian forest,It is also the dominant tree species of desert riparian forest in arid area of northwest China.It has strong characteristics of drought and salt resistance,It plays a very important role in the prevention and control of desertification and the maintenance of desert ecological balance.Therefore,it is urgent to Attach importance to and strengthen the protection,recovery and development of P.euphratica,and to explore and grasp the growth mechanism and physiological and ecological adaptive characteristics of P.euphratica to adapt to the environment is an important premise for the protection of P.euphratica.This study took P.euphratica in Ejina Banner of Inner Mongolia as the research object.From the perspectives of population,individual and molecule,the characteristics of population structure,chemical elements and metabolic compounds of heteromorphic leaves,physiological and ecological functions and transcriptomics of P.euphratica were studied in order to reveal the ecological strategies and the adaptation mechanism of ontogeny growth and development to the drought environment in the process of leaf shape change.The main research results are as follows:(1)The population characteristics of Populus euphraticaThe population age structure of P.euphratica was greatly affected by environmental conditions.The age structure of P.euphratica population was spindle-shaped,and the proportion of young age was relatively large,and the population tended to be stable.Due to water stress in Badaqiao and Badain Jaran Desert,the population age structure of P.euphratica in Badaqiao and Badain Jaran Desert showed an inverted pyramid shape,and the population was mainly aged,the young plants were missing,and the population was in decline.The height of P.euphratica trees was greatly affected by the environment,and the height of P.euphratica plants decreased due to water stress.Population near the river was relatively stable in height class and grew well.Under drought conditions,the number of height grades at near maturity was scarce,while the number of height grades at young maturity was missing,and the growth condition was poor.The population density of P.euphratica decreased with the increase of diameter class.The regeneration resources of P.euphratica population in Qidaoqiao are abundant and the population can keep steady growth in the future.The population of P.euphratica in Badaoqiao and Badain Jaran Desert is dominated by overmature trees and will decline in the future.(2)The ecological stoichiometry and plant metabolism of Populus euphraticaThe contents of chemical elements and the ecological stoichiometry characteristics of the leaves of different forms of P.euphratica showed great differences,and the plant leaves showed different nutrient ecological adaptation strategies at different developmental stages.The content of organic carbon in the leaves of P.euphratica was more than 400 mg·g-1.The average contents of N,P,C/N,C/P and N/P were 13.87 mg·g-1,2.4 mg·g-1,32.62 mg·g-1,190.20 mg·g-1 and 5.93 mg·g-1,respectively.The contents of chemical elements were C>N>P.and the stoichiometric ratio was C/P>C/N>N/P.There was an extremely significant positive correlation between C/P and N/P,and an extremely significant negative correlationbetween N and C/N,and between P and C/P and N/P.There was significant positive correlation between N and P,C/N and C/P,and significant negative correlation between N and C/P,P and C/N.The content of C in P.euphratica at different developmental stages and different leaf morphology remained at a relatively stable level,There was no significant difference and the coefficient of variation was small.The coefficient of variation of C/P and P were the largest.the contents of chemical elements in the leaves of different forms of Populus euphratica showed certain differences,but there was no significant relationship between the contents of chemical elements in the leaves of P.euphratica at different stages of development,which indicated that the content and ratio of chemical elements in the leaves of P.euphratica were greatly affected by the leaf form,but were relatively stable with the development of stand age.P.euphratica leaves contains sugar,fat,amino acids,such as a variety of secondary metabolites,different development phase compounds have different types and levels of the plant,but the same plant different leaf shape difference is small,this suggests that the main metabolic compounds in distribution in the body with the plant growth,development and change,and in the same plant growth process is relatively stable.(3)The physiological and ecological characteristics of Populus euphratica The same leaf shape of P.euphratica at different development stages showed a different pattern due to its position and development stage,which showed that the leaves growing in the upper part of the crown had stronger photosynthetic capacity.Different leaf shapes of P.euphratica at the same development stage had obvious temporal and spatial variation characteristics,and the photosynthetic capacity of tree crown increased successively from bottom to top.Different leaf shapes at the top of the tree crown at different stages of P.euphratica development also showed obvious changes:among them,the strip-shaped leaves of the seedlings maintained a higher light energy utilization and a higher photosynthetic rate.In response to high temperature stress,the stomatal closure of the sapling-lanceolate leaves,mid-lanceolate leaves,and wide-ovate leaves of P.euphratica was forced to reduce water consumption,and a short "photosynthetic nap"appeared around noon,and the transpiration rate was in line with the stomatal changes,and the light and nap rest were mainly restricted by stomatal changes.The spatial variation of leaf light response of the same plant showed that the photosynthetic rate increased successively from bottom to top.CP grew at the bottom of the tree canopy and had a strong weak light utilization ability.Similarly,the stripe leaves had lower a and relatively higher LCP,LSP and Pnmax,and a wide range of light energy utilization enabled them to maintain a higher photosynthetic rate under low light environment.The broad-oval leaves of The mature plants have higher photosynthetic activity.By increasing PNmax,the light energy utilization rate can be enhanced,so that the light energy conversion efficiency and photosynthetic rate can still be maintained higher in the arid desert area under high temperature and strong light environment.(4)The transcriptome sequencing and differential gene analysis of Populus euphraticarelationship between the omics difference of P.euphratica adaptation to the environment and the individual growth and development showed as follows:Using P.euphratica seedlings(YM-T)as reference,we compared them with other 6 morphological leaves for transcriptome differential gene analysis.After assembly clustering and redundancy removal of 14 samples,543653 Unigenes were obtained.Through inter-group differential gene analysis,a total of 43143 differentially expressed genes were found,among which 22376 were upregulated,20767 downgrades.Among them,the most differentially expressed genes(including up-regulation and down-regulation)were found in broad-ovate leaves of adult trees.The GO enrichment analysis showed that the regulation mechanism of P.euphratica adaptation to the environment was mainly biological regulation processes such as related metabolism and enzyme activity.KEGG enrichment analysis showed that the differential genes were significantly enriched in flavonoid biosynthesis,terpenoid biosynthesis,nitrogen metabolism,photosynthesis,amino acid metabolism and other pathways.Further analyses MapMan gene,to get difference results show that the genes involved in photosynthesis regulation is mainly the protein subunits in light lighting system II complex coding genes and Calvin cycle of Rubisco activity most photosynthesis related enzyme activity.such as the above results can provide theory for further screening of P.euphratica art gene. |
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