Physiological and Ecotypic Adaptations of Plants to Salt Desert Conditions in Utah

Abstract

Ecotypic variation has been found recently in several salt desert plant species (Workman & West 1967, 1969; Clark & West 1971; Goodman & Caldwell 1971). This finding is interesting, since it is difficult to explain the distribution of desert plants on any other basis (Gates, Stoddart & Cook, 1956; Mitchell, West & Miller 1966; Gasto 1969). Plant distribution is itself economically important since the forage value of the species varies widely and the proportion of useful species determines the grazing value of the desert rangeland. Two kinds of distribution of desert species need to be explained. The more striking of these is the mosaic distribution which covers large areas. Each piece of the mosaic is a few hundred metres in diameter and differs slightly from its neighbours in species composition or dominance. The second distribution pattern concerns the subdominant species. Some of these have a much wider distribution than the dominants and are thinly spread over areas where the soil conditions, such as salinity, may vary eighty-fold. This represents an unusually high degree of tolerance and is, in a sense, the opposite problem to the perplexingly restricted range of the mosaic-dominant species of the same habitats. This paper describes an investigation of these complex situations directed particularly to finding whether the existence of a range of ecotypes could contribute to making artificial boundaries between communities in the mosaic zone, or could blur the boundaries between communities of the tolerant species. The investigation had three stages. First, several species were measured for growth and nutrient response in different situations where ecotypes might occur, in the field at Curlew Valley, in north-western Utah. Secondly, typical plants were brought from the possible ecotype situations into uniform laboratory culture and compared for growth and, thirdly, the possible ecotypes were given graded salt concentrations to test their interaction with different environments in the laboratory, and to relate these to their field behaviour.