Exploring water relations and phenological traits of Betula utilis (D. Don) in western Himalayan treeline ecotone

Betula utilis exhibits intriguing characteristics and interactions with its environment and has specific adaptations that enable it to thrive in various water conditions. Drought has a prominent role in influencing the growth and development of vegetation, while temperature serves as a crucial determinant of species distribution in high-altitude environments. The investigation was centered on the eco-physiological dimension of B. utilis in areas near the treeline. Across different seasons, sites, and years, the most negative pre-dawn twig water potentials (Ψ_PD) and mid-day twig water potentials (Ψ_MD) were - 0.81 and - 1.24 MPa, respectively. The highest seasonal change (ΔΨ) in twig water potential (Ψ_twig) was in the post-monsoon season. Osmotic potential at full turgor (Ψπ₁₀₀) declined by - 0.66 MPa and osmotic potential at zero turgor (Ψπ₀) declined by - 1.07 MPa. The highest leaf conductance (gw) of 380.26 mmol m^-2 s^-1 was measured in the afternoon. During the initiation of flowering, Ψ_PD of the twig was - 0.72 MPa and gradually rose to - 0.17 MPa by the end of the flowering period. This study provides key insight into the Ψ dynamics, leaf conductance, and phenology of B. utilis, highlighting its adaptation to changing environmental conditions and the need for effective management strategies to ensure the resilience and conservation of this Critically Endangered species.