The Water Relations of the Alga Cyanidium caldarium in Soil

Abstract

SUMMARY: The effects of water potential on the photosynthesis, growth and viability of natural populations and laboratory cultures of Cyanidium caldarium were measured. C. caldarium was very sensitive to reduced water potential, matric reduction being more harmful than osmotic. The distribution of this alga in different soil areas appeared to be related to the sensitivity to water stress, larger populations being found in areas with higher water potential. There are very steep gradients of water potential in the soils where Cyanidium caldarium is found. The water potential of the surface crust is much too low to allow growth and C. caldarium is found in a subsurface layer. The reduced light intensity below the soil surface interacts with the increased water potential to define the position of the algal layer.