| To achieve the goal of "carbon neutrality",it is imperative to excavate high-carbon sequestration tree species,select and cultivate high-carbon sequestration germplasm resources.Fraxinus mandshurica is an important industrial timber and ecological tree species in China.It is a selected tree species for the national reserve forest.At present,the research on the selection and breeding of Fraxinus mandshurica was mostly concentrated on the aspects of growth and stress resistance evaluation,and high-growth Fraxinus mandshurica varieties had got obtained.However,the research of selective breeding and genetic improvement with the goal of carbon sink has just started,which has caused the structural deficiency of the improved species of Fraxinus mandshurica,and there is no improved species of Fraxinus mandshurica with high carbon sequestration.Studies have shown that Fraxinus mandshurica has a high potential in carbon sink forestry applications.To study the variability of carbon storage of Fraxinusmandshurica,select and promote high-carbon sequestration varieties of Fraxinus mandshurica,and analyze the molecular mechanism of carbon storage differences between provenances,this paper studied the overall variation of carbon storage and growth characteristics of Fraxinus mandshurica as well as the variation of all traits among provenances.And high carbon sequestration provenance selectiong and provenance zoning was also carried out.What's more,the tolerance of high and low carbon sequestration provenances to low nitrogen and phosphorus stress was evaluated.Finally,the molecular mechanism of carbon sequestration of high carbon sequestration provenance was analyzed,including the analysis of the difference in gene transcription level between high and low carbon sequestration provenances,and the regulatory network model of high carbon sequestration genes of Fraxinus mandshurica was drawn.FmbHLH35 and FmbHLH36 genes were highly expressed in high-carbon provenance and the effect of overexpression of FmbHLH35 and FmbHLH36 genes on tobacco growth was anlized.The main findings of this article were as follows:1.Study on the overall variation law of the provenance test forest of Fraxinus mandshuricaFocusing on the traits related to carbon sequestration,this study focused on two typical ecological regions(Maoershan and Dailing)to compare the genetic variation of 360 analytic trees in 50 traits in 14-year-old experimental forests from 20 provenances.The results show that the variation pattern of carbon traits between tissues was gradually decreasing from the trunk to the morphological ends of the tree.Compared with the Maoershan site with a better habitat,the Dailing site with a poorer habitat reduced carbon amount by 60.43%.Geographic variation analysis of the provenance of Fraxinus mandshurica showed that the carbon content presented a basic pattern of northwest-southeast direction and vertical gradient variation of altitude:the higher the latitude,the higher the altitude,and the smaller the longitude,the greater the carbon concentration.Among all meteorological factors that affected the biological characteristics of Fraxinus mandshurica,temperature variation dominated.Allometric growth models for estimating the carbon amount of different tissues based on diameter at breast height(DBH)was established.There were 4 tissues with a model fit of 0.85 or higher,which were individual plant(Y=111.59×DBH2.048,R2=0.860),aboveground part(Y=76.01×DBH3.096,R2=0.864),tree trunk(Y=59.08×DBH2.007,R2=0.860)and trunk wood(Y=43.68×DBH2.075,R2=0.851).These results jointly revealed the variation of biological characteristics of different provenances of Fraxinus mandshurica and laid the foundation for the selection of high-carbon provenance.2.Selection of high carbon sequestration provenanceIn this study,carbon amount was used as the main indicator,while growth traits,morphological traits,and carbon concentration were as limiting factors which were not less than the total average value.The high carbon sequestration provenances of Fraxinus mandshurica were selected in two ecological regions.The results showed that Maoershan provenance(local provenance)and Suiling provenance were the provenances with the highest carbon sequestration capacity in the Maoershan site and the Dailing site respectively,and their individual plant carbon amount exceeded the total average value by 26.81%and 29.65%respectively.If the selected high-carbon provenances were used for afforestation in the two ecological regions represented by the Maoershan site and the Dailing site respectively,calculating based on the existing density of the provenance test forest(3300 plants/ha),the carbon sequestration per hectare will be 4131.6 kg and 2847.9 kg more than the total average value,respectively.Through principal component analysis,all growth traits of the two sites were integrated into one growth factor,the first principal component.According to the scores of 20 provenances on the first principal component,Maoershan,Zhanhe,and Wuchang provenances were selected as the two site high-carbon provenance provenances,and their carbon amount exceeded the total average by 19.9%,18.7%and 10.6%,respectively.The selected high-carbon sequestration provenance made up for the lack of structure of the fine varieties of Fraxinus mandshurica,and provided elite provenances for the construction of high-carbon sequestration seed gardens and high-carbon sequestration plantations.3.Fraxinus mandshurica provenance regionalization based on growth traits,morphological traits,carbon traits,and climate and ecological factorsAccording to the scores of 20 provenances on the first principal component,combine the regionalization results of ecological factors and the topographical features of the distribution of Fraxinus mandshurica in Northeast China,and then select biological traits with significant differences between provenances to perform principal component analysis for provenance zoning of biological traits.The 20 provenances of Fraxinus mandshurica were divided into 4 provenance areas from south to north:the provenance area in the south of Changbai Mountain(Hengren,Wandianzi,Sanchazi,Linjiang,Xifeng,Huinan,Lushuihe),the provenance area in the north of Changbai Mountain(Wangqing,Hailin),the provenance area in the Songhua River Basin(Wuchang,Maoershan,Fangzheng,Huanan,Dongfanghong),and the provenance area in the Xiaoxing'an Mountains(Xinglong,Suiling,Dailing,Youhao,Zhanhe,Tangwanghe).This will provide guidance for the allocation of Fraxinus mandshurica seeds,and achieve proper local and provenance in the practice of introduction of Fraxinus mandshurica.4.Analysis on the adaptability of high and low carbon sequestration provenance to nitrogen and phosphorus deficiencyThrough the sand culture experiment under the treatment of low nitrogen(N-)and low phosphorus(P-)to high and low carbon sequestration provenances,the difference between high and low carbon sequestration provenances in tolerance to low nitrogen and low phosphorus was studied.The results showed that the tolerance to N-or P-for high-carbon sequestration provenance was greater than that of low-carbon sequestration provenance.Under low P condition,especially under low phosphorus condition,high carbon sequestration provenance could maintain relatively high biomass growth.The specific performance was as follows:the dry weight,nitrogen amount per plant,and leaf area of high-carbon sequestration provenance were significantly larger than low carbon sequestration provenance,which was attributed to the higher chlorophyll content,PEPC enzyme activity,transcription level of genes in both leaves(NRT2.1,NRT2.7,NIA2 and PHO1;H1)and roots(NIA2,PHT1-3,PHT1-4 and NRT2.5).The high tolerance of high carbon sequestration provenances with low nitrogen and low phosphorus provided theoretical support for the promotion of high carbon sequestration provenances.5.Analysis of the molecular mechanism of the difference in carbon traits between high and low carbon sequestration provenancesThrough transcriptome analysis of high and low carbon sequestration provenances under complete nutriton,783 differentially expressed genes(DEGs)related to high carbon sequestration were identified.The number of DEGs in leaves(669)was 4.5 times that of roots(149),so the DEGs in leaves were the main reason for the difference in carbon traits of provenance.Based on the literature and gene transcription level,a model map of the gene regulation network of the high carbon sequestration traits of Fraxinus mandshurica was proposed.From the transcription level of genes such as carbon metabolism enzymes,small molecule signal substances trehalose and expansin,cell wall metabolism enzymes,and key metabolic enzymes in the phenylpropane metabolism pathway,the molecular mechanism of the differences in carbon traits of provenance was analyzed.The overexpression of FmbHLH35 and FmbHLH36 genes significantly increased the dry weight of tobacco by 1.04 times and 2.16 times,which was related to the enhancement of biosynthesis ability of transgenic tobacco by increasing the distribution of above-ground biomass.The identification and screening of DEGs between high and low carbon sequestration provenances and the verification of the promotion effect of FmbHLH35 and FmbHLH36 genes on growth provide genetic resources for forest tree molecular genetic breeding. |
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