Investigation of some morphological and physiological traits of yew leaf in the Arasbaran region to propose some management strategies

Background and objectives: Due to the low number of yew (Taxus baccata L.) habitats in the Arasbaran forests, the low regeneration of the species, its threat, its high medicinal value, and the preservation of the natural landscape of the region add to the importance of this valuable species and intensify the need for its conservation. However, there is a lack of detailed information on the genetic diversity of the species in this region. Determining the superior population for the development of plantations, learning about genetic erosion, and assessing the potential of populations are other priorities for forestry research. The primary objective of this research was to identify a population of Arasbaran yews with reduced genetic diversity, allowing for the development of management practices to enhance genetic diversity in this vulnerable population.
Methodology: Two major yew habitats in the Arasbaran region were selected, namely the Kalaleh village located in Khoda Afrin city and the Kuran village located in Horand city. In each habitat, 20 healthy yew trees were randomly selected and 20 healthy leaves were collected from each tree from the middle of two-year-old branches (from the right and left sides of the branches), from the middle part of the crown tree, and also the outer region of the crown (north and south). A total of 800 leaf samples were imaged. Leaf morphological traits, including leaf area (cm2), leaf perimeter (cm), leaf length (cm), and leaf width at 50% of leaf length (cm), were measured. The leaf index was calculated from the ratio of leaf length to leaf width at 50% of leaf length. Also, leaf index, relative water content, specific leaf area (cm2/g), leaf dry weight, and leaf mass per area (g/cm2) of leaf samples were calculated. A nested analysis of variance was performed between populations. Then, environmental variance, genetic variance, phenotypic variance, heritability, phenotypic coefficient of variation, genetic coefficient of variation, and both genetic and phenotypic correlations were calculated. Principal component analysis was performed to determine the traits that had the highest percentage of variance.
Results: The results revealed significant differences in leaf area, specific leaf area, leaf index, specific weight, and dry weight at the 95% and 99% confidence levels across different populations. The results showed that the mean values of the leaf area, specific leaf area, leaf perimeter, and relative water content were higher in the Kalaleh population than in the Kuran population. In contrast, the highest values of the traits, including leaf index, Leaf mass per area (LMA), and dry weight, were observed in the Kuran population. The results showed that in both populations, the trait-specific leaf area had the highest genotypic variance. The highest coefficient of genetic and phenotypic variation was observed in the Kalaleh population for the dry weight trait, and the lowest coefficient of genetic variation was observed in the Kalaleh population for the relative water content trait. The lowest coefficient of phenotypic variation was observed in the Kuran population for the trait related to leaf index. The heritability of the traits was more than 50 percent in the Kalaleh population for the trait leaf perimeter. For the Kuran population, the heritability of all the studied traits was more than 50 percent. For the Kuran population, the heritability for leaf area and leaf perimeter traits was more than 50%. The genetic variation coefficient for the Kalaleh population was greater than 20% only for the dry weight trait, and for the Kuran population, the genetic variation coefficient for all studied traits was less than 20%. The highest significant genetic correlation was observed in the Kuran population (-0.985) and Kalaleh (-0.981) between specific leaf area and specific weight traits. Also, in the Kuran population, the highest positive and significant correlation (0.9808) was observed between the leaf area and leaf perimeter. The results of the study of genetic and phenotypic correlation in the populations showed that in most traits, the genetic correlation between traits were greater than the phenotypic correlation, so that the highest positive genetic correlation (0.9808) was observed between the leaf area and leaf perimeter. The highest positive and significant phenotypic correlation (0.8628) for the populations was observed for leaf area and leaf perimeter, and a negative and significant phenotypic correlation (-0.923) was observed between specific weight and specific leaf area. In the principal component analysis, the first two components accounted for more than 99.2% of the total variance. The specific leaf area played a more important role in the formation of the first component. In relation to the second component, the relative water content played a more important role.
Conclusion: According to the results of this study, field observations, and also accepting the assumption that if the genetic diversity of a population is lower than other populations of the species, that population is weaker, it can be suggested that since the genetic diversity of yews in the Kalaleh population is lower than that of the Kuran population, several seeds (at least 30 seed trees) from the superior Kuran population should be transferred to the weaker Kalaleh population, which enhances gene flow between populations and can compensate for the genetic diversity lost in the Kalaleh. Additionally, installing nets around the isolated yew seedlings in the Kalaleh population is advised to provide protection. To safeguard the yews outside their natural habitat, samples from the Kuran yews population, which has higher genetic diversity, should be selected for propagation and planted under the shade of tall trees in the Botanical Garden of the University of Tabriz and Abbas Mirza Forest Park in Tabriz. Finding the best source of yew seeds by examining the genetic diversity of seed traits is also recommended.