Effect of Water Potential on a Microcoleus (Cyanophyceae) From a Desert Crust¹

SUMMARY The effect of water potential, on the growth and photosynthesis of a species of Microcoleus forming a desert crust was determined, using both osmotic and matric variations in water potential. The alga was quite sensitive to moisture stress, partial inhibition of growth being observed at ‐7 bars, and complete inhibition at ‐18 bars. Photosynthesis was markedly inhibited at ‐18 bars, and virtually completely at, ‐28 bars (water potential of seawater) and lower. The alga was more sensitive to matric reduction in water potential than osmotic. By comparisons of these results with those obtained with other algae, it is concluded that this desert crust alga is not especially adapted to grow and photosynthesize at low water potentials, although it shows considerable ability to survive severe drought conditions.