The effects of water stress on some growth and chlorophyll a fluorescence parameters were investigated in two native black poplar (Populus nigra L.) clones (Kocabey and Gazi) and in two hybrid poplar (Populus x euramericana (Dode) Guinier) clones (I-214 and I-45/51) to determine which among the four clones is the best adapted to water-stress conditions. The potted seedlings were grown under three watering regimes. As a result of the applied watering regimes, the predawn water potential (psi(pd)) of seedlings was maintained at about -0.3, -0.9, and -1.6 MPa in control, moderate, and severe water-stress treatments during the experiment, respectively. Drought treatment had significant effects on the morphology and growth characteristics of the clones but had generally insignificant effects on survival and the photochemical activity of photosystem II (PSII). Results obtained from the present study demonstrate that I-214 was the most successful in terms of its higher root/shoot ratio (R-s), maximum fluorescence yield (F-m), maximum quantum efficiency of PSII (F-v/F-m) values, and lower number of leaves among the examined four poplar clones under drought stress conditions. Consequently, the I-214 poplar clone may have the potential to be used in drought areas.