Alfalfa water status and cold hardiness as influenced by cold acclimation and water stress

Water stress at a nonacclimating temperature (18–20°C) increased the cold hardiness of Medicago sativa L. (alfalfa) plants. This increased cold hardiness was retained when the previously water‐stressed plants were cold acclimated (2–9°C) in the absence of water stress. Water stress during cold acclimation also increased cold hardiness. Alfalfa was demonstrated to suffer injury, measured as decreased growth following freezing, at sub‐lethal temperatures. During cold acclimation the turgor potential (ψ) of watered plants increased, whereas the solute potential and the water content per unit dry weight decreased. The large positive psgrdap of acclimated plants indicates that the decreased water content per unit dry weight is related to an increased proportion of tissue dry matter rather than to tissue dehydration.