THE EFFECT OF DEHYDRATION AND ION STRESS ON CARBON-DIOXIDE FIXATION IN DROUGHT-TOLERANT PHOTOTROPHIC MICROORGANISMS

Two cyanobacterial strains, Crinalium epipsammum SAB 22.89 and Tychonema sp. SAB 23.89 and the green alga Klebsormidium flaccidum were examined for their ability to fix carbon during controlled dehydration. Additionally the cyano-bacterium C. epipsammum was subjected to dehydration in the presence of a range of NaCl concentrations in order to discriminate between the effects caused by either matrix or ionic forces. K. flaccidum and C. epipsammun were proved to be able to maintain full carbon-fixing activity until the water content approached zero.Tychonema sp. appeared to reduce its activity in an immediate response to becoming dehydrated. The experiments have further substantiated the view on the strategy of these three drought-tolerant organisms to oscillating water availability. The cyano-bacteria, as the initial colonizers inhabiting the barren sand, are able to react quickly to changing water availability, thereby improving the water retention quality for the green alga. The latter organism will function well in an environment with improved water retention characteristics. C. epipsammum demonstrated extensive differences in carbon-fixing activities during dehydration in the presence of various concentrations of NaCl. This implies that when C. epipsammum is dehydrated in soils low in salt, the water availability, which is given by the matrix water potential, is determining the photosynthetic activity, whereas in more saline soils (equivalent to 50 mM NaCl and higher) the versatility towards osmotic adjustment plays an important role. © 1990.