Differential mechanisms of tolerance towards water stress have been reported in literature, which might be responsible for the variability observed in the parameters examined amongst the isolates (Potts & Bowman 1985; Potts 1994). Similar studies on ecophysiology of desert community particularly on non-heterocystous cyanobacteria have carried out by Potts & Friedmann (1981) who have observed variability in various parameters examined in the strains predominantly harbouring deserts.