Differences in Big Sagebrush (Artemisia tridentata) Plant Stature along Soil-Water Gradients: Genetic Components

Abstract

Genotypic and phenotypic variations are characteristic among big sagebrush (Artemisia tridentata) plants. One obvious expression is the variability of big sagebrush plant stature along soilwater gradients. Large plants are usually associated with mesic habitats such as drainages or swales, while small plants occupy the xeric portions of the gradients. The purpose of this study was to investigate the genetic influence on big sagebrush plant stature along soil-water gradients. Leaf morphological, phenological, chromatographical, and cytological investigations evaluated potential genetic differences and examined possible subspecies status of the large and small plants. The results of these studies revealed a genetic difference between the large and small plants and confirmed subspecies status. The large plants were identified as basin big sagebrush (A. tridentata spp. tridentata) while the small plants were Wyoming big sagebrush (A. tridentata spp. wyomingensis). Three additional studies examined possible differences in growth potential between the subspecies. A greenhouse and uniform garden study compared seedling and juvenile plant growth. Annual leader growth of mature plants was measured in native populations. Basin big sagebrush plants outgrew Wyoming big sagebrush in the greenhouse, uniform garden, and leader growth experiments. Difference in growth potential between the subspecies may be a consequence of ploidy differences. The most common, important, and widely distributed woody sagebrush (Artemisia L. subgenus tridentatae (Rydb.) E.D. McArthur) is big sagebrush (Artemisia tridentata Nutt.). Big sagebrush is common on millions of hectares throughout western North America from southern Canada to northern Mexico (Beetle 1960, McArthur et al. 1981). This shrub has a wide range of adaptability and grows in various soil types and is associated with numerous plant species from low elevation valleys and plains to high mountain slopes and ridges (Morris et al. 1976, Winward and Tisdalel977, Winward, 1980). Big sagebrush provides browse and habitat for an array of wildlife and livestock, minimizes soil erosion, and is of value in mined-land reclamation. Big sagebrush, as do other plant species, adapts to diverse environments through a combination of phenotypic plasticity and genotypic variation. As Caldwell (1979) theorized, the phenotypic diversity of plants is remarkable, but it is not sufficient to accommodate extensive environmental conditions that are found in the range of a widely distributed species such as big sagebrush. Presently, the big sagebrush complex consists of 4 subspecies (Beetle 1960, Beetle and Young 1965, Goodrich et al. in press, McArthur 1983) which are: basin big sagebrush (A. tridentata Nutt. ssp. tridentata), Wyoming big sagebrush (A. tridentata Nutt. ssp. wyomingensis Beetle and Young), mountain big sagebrush (A. tridentata Nutt. ssp. vaseyana (Rydb.) Beetle), and subalpine sagebrush (A. tridentata Nutt. ssp speciformis (Osterhout) Goodrich and McArthur). Authors are former graduate research assistant and professor, respectively, Department of Range Science, Utah State University, Logan. Authors are presently, lecturer, Department of Botany and Range Management, Somali National University, Mogadishu, Somalia and Vice-President for Research, NPI, 417 Wakara Way, Salt Lake City, Utah 84108. Research was supported by the U.S. Department of Energy and Ecology Center and Department of Range Science, Utah State University. We thank E.D. McArthur for technical assistance, use of laboratory equipment, and review of a draft manuscript. Manuscript accepted 3 July 1985. Genotypic and phenotypic variation is characteristic of big sagebrush (Beetle 1960, Hanks et al. 1973, McArthur et al. 1981, West et al. 1978). An obvious expression is the variability in big sagebrush plant stature along soil-water gradients (Beetle 1960, Hall and Clements 1923, Hanks et al. 1973). Large plants may reach a height of 3.5 to 5.0 m in mesic habitats such as drainages or swales, while plants less than 1.0 m tall are associated with the xeric portions of moisture gradients. Considering the differences in big sagebrush plant stature, a logical question arises: Are the differences in plant stature due to genetic or environmental influences? The research herein discusses the influence of genetics on big sagebrush plant stature. Edaphic differences associated with the large and small big sagebrush plants are reported elsewhere (Barker 1981, Barker and McKell 1983).