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

Background and Objective: The scarcity of English Yew (Taxus baccata L.) habitats in the Arasbaran forests, coupled with its low natural regeneration, endangered status, high medicinal value, and critical role in maintaining the region's ecological landscape, underscores the importance of this valuable species and the urgent need for its conservation. Despite its significance, precise data regarding the genetic diversity of Yew in this region is currently unavailable. The primary objective of this study was to identify Yew populations in the Arasbaran region that exhibit lower genetic diversity in order to propose management strategies aimed at enhancing the genetic levels of these vulnerable populations.
Material and Methods: Two primary Yew habitats in the Arasbaran region, Kalaleh-ye Olya village (Khoda Afarin county) and Kuran village (Horand county), were selected for this study. In each habitat, 20 healthy trees were randomly selected. From each tree, 20 healthy leaves were collected from the middle of two-year-old branches (both left and right sides), the middle canopy, and the outer canopy (both northern and southern aspects). A total of 800 leaf samples were imaged. Morphological traits, including leaf area (cm²), perimeter (cm), length (cm), and width at 50% of the length (cm), were measured. Additionally, the leaf index, relative water content (RWC), specific leaf area (SLA, cm²/g), dry weight, and specific leaf weight (g/cm²) were calculated. A nested Analysis of Variance (nested ANOVA) was performed to compare the populations. Subsequently, environmental variance, genetic variance, phenotypic variance, heritability, phenotypic and genetic coefficients of variation, and genetic and phenotypic correlations were calculated. Finally, Principal Component Analysis (PCA) was conducted to identify the traits contributing most significantly to the total observed variance.
Results: The results indicated significant differences (at 95% and 99% confidence levels) for leaf area, Specific Leaf Area (SLA), leaf index, specific weight, and leaf dry weight across the different Taxus baccata populations. The mean values for leaf area, SLA, leaf perimeter, and Relative Water Content (RWC) were higher in the Kalaleh population compared to the Kuran population. Conversely, the highest values for leaf index, specific weight, and dry weight were observed in the Kuran population. In both populations, SLA exhibited the highest genotypic variance. In the Kalaleh population, the highest genetic and phenotypic coefficients of variation (GCV and PCV) were recorded for dry weight, while the lowest were found for RWC. The lowest PCV in the Kuran population was associated with the leaf index trait. Heritability exceeding 50% was observed only for leaf perimeter in the Kalaleh population, whereas in the Kuran population, heritability for both leaf area and perimeter surpassed this threshold. The GCV for the Kalaleh population exceeded 20% only for dry weight, while for the Kuran population, the GCV for all studied traits remained below 20%. The highest significant genetic correlations were observed between SLA and specific weight in both the Kuran (r = −0.985) and Kalaleh (r = −0.981) populations. Additionally, the Kuran population showed its highest significant positive correlation (0.9808) between leaf area and leaf perimeter. Analysis of genetic and phenotypic correlations across populations revealed that genetic correlation values were generally higher than phenotypic correlations for most traits, with the highest positive genetic correlation (0.9808) recorded between leaf area and leaf perimeter.
Conclusion: Based on the results of this study, field observations, and the premise that populations with lower genetic diversity are inherently more vulnerable, it can be concluded that the Yew population in Kuran exhibits lower genetic diversity compared to the Kalaleh population. Consequently, it is recommended that seeds from at least 30 seed-bearing trees from the superior Kalaleh population be transferred to the Kuran site. This intervention would effectively enhance gene flow between populations and help compensate for the loss of genetic diversity in Kuran. Additionally, installing protective netting around isolated Yew saplings in the weaker Kuran population is advised. For ex-situ conservation efforts, samples from the genetically diverse Kalaleh population should be selected for propagation and planted under the canopy of established trees at the University of Tabriz Botanical Garden and Abbas Mirza Forest Park in Tabriz. Finally, further research into the genetic diversity of seed traits is suggested to identify the optimal seed sources for future restoration projects.