Influences of temperature and water stress on germination of plains rough fescue

Abstract

Germination of 12 collections of pIains rough fescue (Festuca altaica Trin. subsp. hallii (Vasey) Harms) from Saskatchewan was evaluated in 55 constant and alternating temperature regimes ranging from 0 to 44 C. Combined influences of temperature and water stress on germination were studied by incubating seeds in a gradient of osmotic potentials at constant temperatures of 5, 10, 15, 20, and 250 degrees C and under regimes where temperatures were either increased from 10 to 25 degrees C or decreased from 25 to 100 degrees C. Seeds germinated in 80 to 87% of the 55 temperature regimes tested with maximum total germination between populations ranging from 34 to 100%. Germination was highest most often at constant temperatures of 15 and 20 degrees C, but seeds germinated over a wide range of temperatures. Germination rate and total germination responded to the interacting effects of temperature and osmotic potential. Under constant temperatures, 71 to 88% of the variation in germination was accounted for by osmotic potential. Seeds germinated fastest, in the highest numbers, and over the broadest range of osmotic potentials at 10 to 20 degrees C. Germination was higher and more rapid over the range of osmotic potentials when temperatures increased from 10 to 250 degrees C than when they declined from 25 to 10 degrees C. Osmotic potential accounted for 65 to 74% of the variation in germination. The plastic response of germination to temperature suggested that while this factor does not limit regeneration of plains rough fescue from seed, germination is severely restricted by declining osmotic potentials. These moisture limitations reflected adaptations that preclude germination under conditions of transient moisture or low moisture availability. Plains rough fescue should be pbted in the spring when temperatures are rising and soil moisture is highest.