Desiccation independence of terrestrialNostoc commune ecotypes (cyanobacteria).

The subspeciesNostoc commune var.flagelliforme andN. commune var.commune are found in China (Ningxia Province, Inner Mongolia) as two morphologically different ecotypes of the desiccation-independent cyanobacteriumN. commune. The first ecotype, but not the second, colonizes arid areas. Various biochemical parameters and water dependence of photosynthesis and nitrogen fixation were compared for both ecotypes. Different patterns of water stress proteins were found in the two ecotypes. Repeated desiccation resulted in an enhanced desiccation independence for photosynthesis and, in the case of the ecotypecommune, for nitrogen fixation. The different response of nitrogenase of both ecotypes towards repeated cycles of rewetting and desiccation under conditions simulating the natural environment is discussed in terms of the energy balance of the colonies that are adapted to different environmental conditions.