| Summary: | This paper measured the ecophysiological responses of Populus cathayana Rehd., Salix longistamina C. Wang et P. Y. Fu., and Ulmus pumila L. to high altitude in the Tibetan Plateau based on changes in water relations, gas exchange, and chlorophyll fluorescence. P. cathayana and U. pumila have higher survival rates than S. longistamina, but the latter has highest biomass. S. longistamina has higher water-use efficiency (WUE), lower transpiration rates (E), higher water potential (Ψ), highest light saturation point (LSP) and higher photosystem II (PSII) photochemistry efficiency (Fv’/Fm’) and non-photochemistry quenching (NPQ) than the other species, and is thus adapted to its habitat for afforestation. U. pumila has lower E, light compensation point (LCP), dark respiration (Rd), Fv’/Fm’ and electron transport rate (ETR), with higher Ψ, apparent quantum yield (AQY), net photosynthetic rate (Pn) and non-photochemical quenching (NPQ), which helps it maintain water balance and utilize weak light to survive at high altitude. Relative low WUE, Ψ, Rd, NPQ, with high E, Pn, Fv’/Fm’ and biomass, imply that P. cathayana is more suitable for shelterbelt forests than for a semi-arid habitat. These three species can adapt to high-altitude conditions by different physiological mechanisms and morphological characteristics, which can provide a theoretical basis for afforestation and forest management in the Qinghai Tibetan Plateau.
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