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Variation in growth, physiology and ionic relations patterns of Allenrolfea occidentalis, a perennial halophyte of dry habitats, was studied under field conditions from May 1996 to November 1997. An A. occidentalis community has a characteristic soil pH of 7.3-8-3. During the two years, the population was exposed to great variations in soil salinity, from 29 to 146 dS m(-1), and soil moisture, ranging from drought (9.2%) to wet (19%). The salt concentrations were significantly higher in the surface soil layers than in the subsurface layers. Seasonal changes in dry weight are directly related to soil salinity stress. Allenrolfea occidentalis had greater growth and biomass production under saline conditions. Na+ and Cl- ions were accumulated in plant tissues in much greater amounts than K+, Ca2+, and Mg2+. Soil salinities were significantly reduced at the end of the growing season. Water potentials of the shoots decreased significantly with increasing salinity. The plant (F-v/F-m ratio) was more affected by salinity and irradiation levels during the summer period. (C) 2001 Academic Press.