Ecotypic Adaptation in Sitanion hystrix

Ecotypic differentiation as a response to climatic conditions was studied in an adaptable grass species Sitanion hystrix (Nutt.) J. G. Smith. Twelve collection were obtained from seven states: Arizona, Colorado, Nebraska, Nevada, New Mexico, South Dakota, and Utah. The collection sites varied in elevation from 1,380 to 2,980 m and in annual precipitation from 310 to 739 mm. Plant materials were grown under uniform conditions in a transplant garden and a growth chamber. The effective growing seasons at the original collection sites were apparently as limited by moisture stress as by cold temperatures. Relative phenological development could be predicted by a climatic scale representing temperature and moisture conditions at the original collection sites. Plant size and dry matter production could not be predicted as reliably, suggesting that the primary factors which influence morphological and production characteristics may be more numerous or complex than those which influence penology. The populations represented in this study have adapted to different climatic conditions primarily through variations in timing of phenological development and in rate of growth. No differences in water use efficiency were found. Under uniform conditions: (1) plants from warm, dry habitats flowered early and had low dry matter production; (2) plants from habitats with moderate temperature and moisture conditions flowered latest and had relatively high dry matter production; and (3) plants from cool, wet habitats flowered early and had relatively high dry matter production. Flowering dates of the different collections varied as much as 2 mo.