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Plants that live in the desert playas of the Great Basin must simultaneously tolerate very high concentrations of salt and high temperature. This study characterizes the respiratory metabolism of one species growing in this environment. An isothermal calorimetric method was used to measure the dark metabolic heat rate (q) and CO2 production rate (R-CO2) of stem tissue from Salicornia utahensis grown in the greenhouse or in constant temperature growth chambers at six different concentrations of NaCl solutions ranging from 0 to 1.0 M. Metabolic rates were measured at eight temperatures from 5 to 40degreesC. Temperature and salt dependencies of q and R-CO2 were used to model response of both growth and substrate carbon conversion efficiency. Salt and temperature stresses are not additive, but rather oppose one another, in other words, the higher the salt, the higher the temperature the plants will tolerate and vice versa. The maximum temperature tolerated is an approximately linear function of salt concentration, being about 20 degreesC at 0 M salt and about 32 degreesC at 1 M.. Concentration of the endogenous osmoticant glycinebetaine increased with salt and temperature but only to about 20 C and 900 mM NaCl.