Variability within a native stand of blue grama

Abstract

Considerable variability and patchiness have been observed within sites of native range dominated by blue grama [Bouteloua gracilis (H.B.K.) Griffiths] range at the Central Plains Experimental Range, Weld County, Colorado. Patches containing tall plants of blue grama with many seedstalks were interspersed with patches of short plants with few seedstalks. Differences in plant height were not entirely related to soil properties. Relative differences in plant height among plants collected in the field were maintained when these plants were grown in a greenhouse environment. "Dry spots" (usually 2 to 4 m in diameter) that contain dark-colored, wilted plants have also been observed during dry, hot weather. We found several differences in soil properties that could be responsible for the dry spots. All differences in soil properties were within the range for the soil series of the experimental site, an Ascalon fine sandy loam (Aridic Argiustoll). Sixty-two plants of blue grama were collected based on their variability from a single pasture, increased vegetatively in the greenhouse, and transplanted into a spaced-plant nursery. In the third growing season following transplanting, mean values for measurements on replicated clones ranged from 202 to 719 reproductive culms per ramet, 25 to 46 cm height of reproductive culms, 17 to 24 cm basal diameter, 39 to 93 grams dry matter per ramet, and from 11 June to 20 July for first anthesis. Somatic chromosome numbers were determined for 60 plants and 55 were tetraploids (4x = 40), 3 were pentaploids (5x = 50), and 2 were hexaploids (6x = 60). We concluded that the observed variability and patchiness apparently result from a combination of both genetic and edaphic factors.