A controlled-environment study was conducted with clones of a naturally occurring aspen-poplar hybrid (Populus grandidentata x P. alba Michx.) to determine the independent effects of five soil water potentials and three clones on net photosynthesis, leaf relative turgidity, and the growth parameters of weight, stem height, and leaf area. Net photosynthesis per plant, leaf relative turgidity, fresh and dry weight, stem height, and leaf area increased with soil water potentials from -15 bars to -1/3 bar. At higher soil water potentials all variables decreased. There were significant differences among clones in fresh and dry weight, leaf area, and net photosynthesis per unit weight and leaf area.