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This study investigates the water relations mechanism of Rhododendron campanulatum (D. Don) in treeline areas of the Himalayan region, emphasizing its vital role in ecosystem dynamics. The species, commonly found as krummholz forms at treeline ecotones, exhibits notable population advancement 1.4 m/yr, which could lead to the densification of the ecotone in the future. Seasonal measurements of soil moisture at depths of 15cm, 30cm, and 45cm, as well as pre-dawn (ΨPD) and mid-day (ΨMD) water potentials, and leaf conductance in the forenoon (gwAM) and afternoon (gwPM), were conducted for both trees and seedlings. Significant variations were observed among sites, seasons, and years across various parameters, including soil moisture and water potential components. The study underscores the most negative water potentials (Ψ) during winters, with ΨPD reaching -0.88 MPa for trees and -1.43 MPa for seedlings. Seasonal changes in water potential (ΔΨ) ranged from 0.11 to 0.82 MPa for trees and 0.20 to 0.90 MPa for seedlings. Osmotic potential at full turgor (OPFull) declined from winter to summer, ranging from -0.74 to -1.76 MPa in trees and -0.45 to -1.60 MPa in seedlings. Relative water content (RWC%) of seedlings varied between 68.00% and 87.40%. Leaf conductance ranged from 19.50 to 329.68 m mol m-2 sec-1 in trees and 43.60 to 331.40 m mol m-2 sec-1 in seedlings. The study highlights the adaptation of R. campanulatum and other broad-leaved evergreen species to high-altitude climatic irregularities, emphasizing the crucial role of snowmelt and monsoon rains in mitigating water stress. Osmotic adjustment and high relative water content enable R. campanulatum to cope with environmental changes, maintaining water availability for photosynthesis.