An Analysis of Variation Between Upland and Lowland Switchgrass, Panicum Virgatum L., in Central Oklahoma

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Abstract
Mass field collections and plants grown under various environmental conditions were analyzed to determine the extent of the morphological differences occurring between upland and lowland types of switchgrass, Panicum virgatum L., in McClain County, Oklahoma. The bases for these differences were also investigated. A comparison of field populations revealed differences in clonal habit, in the size of clones, and in the gross morphology of their vegetative organs. Lowland plants were larger in most aspects than those of upland areas although the differences between them were somewhat nullified by variations within each of the two types. Genetically controlled morphological differences became evident when the effects of environmental differences were eliminated. Although upland and lowland switchgrasses were somewhat modified under common greenhouse conditions, they exhibited essentially the same morphological differences as did field populations. A physiological difference in water requirement also occurred between the two types. Lowland switchgrass grew best under flooded conditions, whereas upland plants reached their greatest development under more moderate conditions of soil water. The morphological differences between field populations occurred largely, therefore, as a result of the morphological expression of this physiological difference in water requirement which was superimposed on lesser genetic differences. Upland and lowland switchgrasses also differed in their requirement for nitrogen, the latter having a somewhat lower requirement than the former. This factor probably did not contribute significantly to the existing morphological differences. The results of reciprocal transplants substantiated these conclusions. Plants of the lowland type were tetraploids. Hexaploids and octoploids occurred in the upland with hexaploids being the most common.