Halophytic characteristics and potential uses of Allenrolfea occidentalis

Abstract

Allenrolfea occidentalis (S. Wats.) Kuntze is a C₃ halophytic plant that grows in the arid environment of Western United States where halomorphic soil induces extreme osmotic stress with erratic and low precipitation during the growing period. This perennial species grows well in soils with 6% NaCl. It is one of the most salt tolerant plants in salt playas of the Great Basin in the Western United States. During the hot summer months the salt accumulates in high concentrations on the surface which prevents most plants except A. occidentalis from growing. The highest seed germination was obtained at a thermoperiod of high night (25°C) and high day (35°C). Most of the seeds were salt tolerant and some could still germinate at 600 mM NaCl. The seeds could recover from high salinity when placed in low salinity solutions. Several compounds, fusicoccin, ethephon, nitrate, thiourea, kinetin and gibberellic acid counteracted the inhibition produced by high salinity. Seeds germinated better in the light and at higher temperatures. Some of the growth regulating compounds could alleviate the effect of darkness. Best growth of A. occidentalis was obtained at a density of 1975 plants per m² at 600 mM NaCl. Na⁺ and Cl⁻contributed substantially to the dry mass of the plant. Net photosynthesis increased at lower salinity (200 mM NaCl). The pH of the soil in the salt playa of the Great Basin ranged from 7.3 to 8.3. The salinity ranged from 29 to 146 dSm ⁻¹ and soil moisture ranged from 9.2% to drought conditions. When salinity levels become lower, dry matter production increases and tissue water contents decrease. Allenrolfea occidentalis had greater growth and biomass production under saline conditions. Na⁺ and Cl⁻ ions were accumulated in plant tissue in much greater amounts than K⁺, Ca⁺⁺ and Mg⁺⁺. Good seed production occurred with A. occidentalis and a seed bank was present in the upper layers of the saline soil. The seed bank played a role in maintaining the population of A. occidentalis. Survival of young seedlings was dependant upon the soil moisture level during the hot summer period. The oil content of the seeds of A. occidentalis was about 20%. The fatty acids in the oil was 85% saturated and 15% unsaturated fatty acids. The biomass of A. occidentalis is a potential feed for animals. The wood biomass could be pressed into firewood and particle-board material. The use of halophytes in high salinity soil becomes an appealing choice to obtain some productivity from the land. Many factors are involved in selecting a useful halophyte such as how much salinity can the plant tolerate, can seeds germinate in saline conditions, is there a product of value from the plant?

The Great Basin area in the Western United States has no major drainage system and the runoff water tends to accumulate and evaporate in the valleys. Over a long period of time, the soil has become saline with certain areas developing into salt playa. This has provided selection pressure for the development of salt tolerant plants. We have evaluated one of these Great Basin halophytes.