Wetlands Ecology and Management 9: 463–468, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 463 Seasonal changes in respiration of halophytes in salt playas in the Great Basin, U.S.A. Lyneen C. Harris, Bilquees Gul 1 , M. Ajmal Khan 1 , Lee D. Hansen & Bruce N. Smith ∗ Departments of Chemistry and Biochemistry and Botany and Range Science, Brigham Young University, Provo, Utah 84602, U.S.A.; 1 Current address: Department of Botany, University of Karachi, Karachi-75270. Pakistan; ∗ Author for correspondence: Department of Botany and Range Science, Brigham Young University, Provo, UT 84602, U.S.A.; Tel: 1-801-378-4885; Fax: 1-801-378-7499; E-mail: bruce_smith@byu.edu Key words: Allenrolfea occidentalis, calorimetry, Distichlis spicata, respiration, Salicornia rubra, S. utahensis, salinity Abstract Many desert playas are covered with water in the early spring. As the weather becomes warmer and drier, water evaporates, increasing salt content of the soil from 7,000 to almost 16,000 mmol NaCl Kg -1 . Changes in respir- atory metabolism during the growing season of four halophytes characteristic of cold desert playas was followed using calorimetry. In order of decreasing salt tolerance, the species examined were: the forbs Salicornia rubra, S. utahensis; the grass Distichlis spicata; and the shrub Allenrolfea occidentalis. Tissue collected in the field from sites of low and high salinity in a single playa during May, June, and August of 1997 was put in isothermal calorimeters and the metabolic heat rate (q) and respiration rate (R CO2 ) measured. Efficiency of substrate carbon conversion (q/R CO2 ) and predicted specific growth rate (H B R SG ) were calculated. These species are all well-adapted to the environment in which they are found. Highest metabolism, respiration, efficiency and growth are found during May and June and are lowest during the hot, dry month of August. Differences between the species are also noted. Introduction In the Great Basin of the western U.S.A., the annual precipitation ranges from 10 to 20 cm, mostly as snow with relatively little spring or summer rain. Just east of the town of Goshen, Utah, are a number of playas, which in the spring are shallow lakes with a water depth of a few centimeters. During the hot, dry sum- mer water evaporates leaving a white deposit of salt (mostly sodium chloride) in the central and lowest part of the playa. No vegetation will grow in the salt crust. However around the salt pan grow concentric circles of salt tolerant species. Salicornia rubra, a small annual forb is found nearest the salt pan with the perennial forb, Salicornia utahensis, growing on slightly less saline soil. In turn, the grass, Distichlis spicata, is found on higher ground, with the shrub, Allenrolfea occidentalis, on still higher, slightly less saline soil. While growth of some halophytes is stimulated by salinity (Flowers et al., 1986), most species of halo- phytes are inhibited by high concentrations of salt with none showing optimal growth at seawater concentra- tion (Ungar, 1991). Growth of desert species from Pakistan was promoted by low salinities (Khan et al., 1998). For instance, 425 mM NaCl promoted growth in Cressa cretica, while growth in 850 mM NaCl was not significantly different from control plants (Khan and Aziz, 1998). Great basin halophytes showed a similar promotion of growth at moderate salinities (400 to 600 mM NaCl) with a decline at higher salinities (Gul, 1998). While plant growth depends on acquisition of car- bon and other resources, the rate of growth is de- termined by the processing of resources into structural biomass as predicted by the rate and efficiency of metabolism (Hansen et al., 1998). The objective of this study was to examine differences in respiratory meta- bolism of field-grown material due to changing salt