As a result of predicted climate change, environmental conditions may make woody plant species such as poplars (Populus spp.) vulnerable unless they are sufficiently adaptable to the new environment. This greenhouse study examined the responses of Hill, Northwest, Okanese and Walker hybrid poplar clones to drought, a potential outcome of a changing climate. Plants were grown from cuttings and subjected to two soil moisture treatments; a well-watered treatment and a drought conditioning treatment in which plants were subjected to cycles of soil moisture deficit. The first study examined growth and gas exchange following treatments, while the second study examined concurrent changes in leaf water potential and gas exchange during a period of increasing soil moisture deficit, following treatments.<p> Hill and Okanese plants had reduced shoot:root ratios, possibly leading to more positive plant moisture balances compared to Northwest and Walker plants. Stomatal characteristics related to steady state gas exchange with Okanese plants having stomata predominantly on lower leaf surfaces, and lower stomatal conductance and Northwest plants having relatively large stomata and increased stomatal conductance. Hill and Okanese plants had the most responsive stomata, which began to close at much higher levels of leaf water potential (-0.45 and -0.54 MPa) than Northwest or Walker plants (-1.03 and -0.88 MPa); however, closure was more gradual in Okanese plants. Drought preconditioning resulted in stomatal closure occurring at higher leaf water potentials in droughted Northwest and Walker plants compared to well-watered plants. Regardless of soil moisture treatment, WUE was highest in Okanese and Walker plants. The drought treatment did however lead to increased WUE in Hill and Northwest plants.<p> Overall, Okanese plants appear to be the best adapted to conditions of reduced soil moisture based on growth and physiological traits, while Northwest and Hill seem better suited to areas where moisture deficits are likely to be less frequent or less severe. Results indicate that variability exists in adaptability of hybrid poplar clones to drought, suggesting that there may also be other hybrid clones that are adaptable to reduced soil moisture conditions, which may merit further investigation.

As a result of predicted climate change, environmental conditions may make woody plant species such as poplars (Populus spp.) vulnerable unless they are sufficiently adaptable to the new environment. This greenhouse study examined the responses of Hill, Northwest, Okanese and Walker hybrid poplar clones to drought, a potential outcome of a changing climate. Plants were grown from cuttings and subjected to two soil moisture treatments; a well-watered treatment and a drought conditioning treatment in which plants were subjected to cycles of soil moisture deficit. The first study examined growth and gas exchange following treatments, while the second study examined concurrent changes in leaf water potential and gas exchange during a period of increasing soil moisture deficit, following treatments.<p> Hill and Okanese plants had reduced shoot:root ratios, possibly leading to more positive plant moisture balances compared to Northwest and Walker plants. Stomatal characteristics related to steady state gas exchange with Okanese plants having stomata predominantly on lower leaf surfaces, and lower stomatal conductance and Northwest plants having relatively large stomata and increased stomatal conductance. Hill and Okanese plants had the most responsive stomata, which began to close at much higher levels of leaf water potential (-0.45 and -0.54 MPa) than Northwest or Walker plants (-1.03 and -0.88 MPa); however, closure was more gradual in Okanese plants. Drought preconditioning resulted in stomatal closure occurring at higher leaf water potentials in droughted Northwest and Walker plants compared to well-watered plants. Regardless of soil moisture treatment, WUE was highest in Okanese and Walker plants. The drought treatment did however lead to increased WUE in Hill and Northwest plants.<p> Overall, Okanese plants appear to be the best adapted to conditions of reduced soil moisture based on growth and physiological traits, while Northwest and Hill seem better suited to areas where moisture deficits are likely to be less frequent or less severe. Results indicate that variability exists in adaptability of hybrid poplar clones to drought, suggesting that there may also be other hybrid clones that are adaptable to reduced soil moisture conditions, which may merit further investigation.