Analysis Of Genetic Variation For Multiple Traits And Selection Of Superior Strains Of Cypress Based On A Carbon Sink Perspective

Cypress is an important ecological and carbon sequestration tree species in China,as it has excellent material and adaptability,and grows mainly in poor and difficult terrain such as rocky desertification and stony mountains.However,compared to southern pine and fir conifer species,cypress is slow to grow and the process of genetic improvement is slow,which restricts the cultivation of efficient plantation forests.Clone and family line forestry are currently the main silvicultural tree species for the promotion of good seeds,and genetic selection for superior genotypes can significantly improve the productivity of forest trees.Therefore,in this study,we used 9-year-old cypress clone and family test stands and 32-year-old 1-generation seed orchard offspring family stands as materials to analyse the level of variation in growth traits,estimate heritability（repeatability）and gain levels,resolve the differences in the distribution of biomass and carbon content of each organ,estimate carbon storage,and further construct anisotropic growth equations for carbon content to investigate the growth and carbon sequestration potential of cypress clones and family lines.The main findings of the study are as follows.The main findings of the study are as follows:（1）Genetic variation in growth and material traits in young and middle-aged stands of cypress.The average height,diameter at breast height,and volume of 9-year-old clones were6.09m,6.15cm,and 0.0106m³,with coefficients of variation ranging from 17.52%to43.24%.The average height,diameter at breast height,and volume of family trees are4.12m,4.79cm,and 0.0048m³,with coefficients of variation ranging from 20.92 to 59.31.The clones had obvious growth advantages,and their average height,diameter at breast height,and individual volume were 47.81%,28.39%,and 120.83%higher than the same age family level,respectively.There were extremely significant differences in tree height,diameter at breast height,and individual volume between clones and families（P<0.01）.The repeatability of each character of the 9-year-old clone ranged from 0.651 to 0.756,and the heritability of the family ranged from 0.132 to 0.322.According to the selection rate of10%,the genetic gain of each character of the clone was 24.23%to 82.21%,and the genetic gain of the family ranged from 6.88%to 35.38%.The genetic gain of the clonal DBH,tree height,and volume was 5.22 times,2.05 times,and 2.32 times of the genetic gain of the family,respectively.It was estimated that the ratio of the narrow heritability and the broad heritability of each character was 0.55 to 0.68,with an average of 0.63,This indicated that clones have achieved higher additional genetic gains through non additive effects.The mean values of tree height,diameter at breast height,individual volume,and wood basic density of the offspring of 16 year old excellent cypress trees were 8.27 cm,9.35 m,0.0587 m³,and 0.598 g/cm³,with a coefficient of variation of 3.77%to 92.18%;At 32 years of age,the mean values of tree height,diameter at breast height,individual volume and basic wood density were 17.73 m,17.01 cm,0.26 m³ and 0.55 g/cm³,and the coefficient of variation was 3.55%～105.84%.The heritability range of tree height,diameter at breast height,and individual volume was 0.56～0.63.According to the selection rate of 10%,the genetic gain range was 44.91%～114.09%.（2）Study on the relationship between biomass allocation of various organs and allometry of young Cypress clones and families.The aboveground biomass allocation of clones was 2.12%higher than that of families.Among them,the allocation proportion of trunk biomass of cypress trees was the highest,with clones accounting for 44.36%,but it was 0.60%lower than the family.The allocation proportion of branch biomass of clones was 18.45%,which was 5.55%higher than the family,and the allocation proportion of leaf biomass was 23.22%,which was 2.84%lower than the family;The proportion of biomass allocation in the underground part of clones was2.12%lower than that in the family.Clones mainly allocate biomass at the expense of coarse roots（3.45%lower than the family）,increasing biomass in the aboveground part（86.03%）,mainly by increasing branch biomass（5.55%higher than the family）and fine root biomass（1.34%higher than the family）to maintain growth advantages.The branches and leaves of the clone were mainly in the middle and upper layers,with the proportion of upper layer branches and leaves being 5.20%and 33.64%higher than that of the family,respectively.Using tree height,diameter at breast height and height under branches as indicators,based on the logarithmic transformation form of power function,the allometry growth relationship of biomass was constructed.It was found that the introduction of height under branches as an independent variable could improve the prediction accuracy.The model ln T=k₀+k₁ln D+k₂ln H+k₃ln UBH was selected to predict the biomass best.We evaluated the gain levels of clones and families based on the selection intensity and found that when the selection rate was less than 30%,the actual gain of clone biomass was greater than that of families.As the selection intensity increased,the biomass gain level of families gradually exceeded that of clones.（3）Study on the selection of high carbon fixation strains of Cypress wood.Regardless of the family and clone levels,the diameter at breast height and tree height of young cypress forests were significantly positively correlated with the quantity of young carbon cypress forests,but not significantly correlated with the carbon content.The trunk and leaves were the main components of carbon content in young cypress forests.The selection model ln T=k₀+k₁ln D+k₂ln H+_k3ln UBH had the best prediction effect on the carbon storage of young forests（except for the carbon content in the roots of clones）,which could be used for the early genetic selection of cypress.Based on a 20%selection rate,it was estimated that the genetic gain of carbon content in the clone test young forest was 51.48%,and the family test young forest was 16.14%.Based on volume traits,6 clones and 6families with both fast growth and excellent carbon fixation were selected.It was estimated that the average dry carbon content of 32 year old cypress trees was67.10 kg,and the average carbon density was 47.27%,making them a high carbon sequestration potential tree species.The carbon content showed a very significant difference among families（P<0.01）,and its heritability was 0.604.According to 10%selection intensity,the genetic gain was 82.02%.There was a significant correlation between carbon content and diameter at breast height,tree height,and volume（P<0.05）,while carbon density only had a significant positive correlation with crown diameter（P<0.01）.Combining the four traits of volume,wood basic density,carbon density,and carbon content,a membership function was used to sort and select 5 excellent families with fast growth,excellent material quality,and strong carbon fixation ability based on a 10%selection rate.Volume,density,carbon density,and carbon content were 59.90%,5.08%,1.02%,107.51%higher than the population average.It can be seen that cypress was a tree species with high carbon sequestration potential,and the difference in biomass allocation affects the growth rate.At young and middle age,genetic selection of fast-growing and high-quality genotypes will help to improve the productivity and carbon storage of cypress.