Biomass and Pigment Production in Three Isolates of Azolla I. Response to Water Stress

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Abstract
Two isolates of Azolla Lam. from Colombia, South America, and one from the USA (Florida) were selected for characterization of their growth potentials in certain defined stress environments. These isolates were Amazonian (RAR) and Atlantic coastal (M-3) specimens of Azolla caroliniana Willd and a Floridian variety (LA) of Azolla filiculoides Lam. Osmotic stress (from polyethylene glycol-amended media) and osmotic/salt stress (from seawater-amended media) were the chosen determinants in these trials. Their effects on growth responses were monitored. Initial growth rates of LA and M-3 were stimulated at 1 and 5 ppt seawater salts, relative to growth under control conditions. RAR, however, was generally the most stable isolate in the experiments with seawater-induced ionic stress. LA was most stable in its biomass growth in experiments with polyethylene glycol 6000, but chlorophyll accumulation data were again least affected in RAR. LA survived the longest of the three isolates at a water potential of approximately —10 bars with either seawater (13 ppt salts) or polyethylene glycol (26 per cent). The latter amendment was usually more inhibitory to acetylene reduction rates in RAR and consistently more inhibitory in LA. RAR was tentatively judged by its reactions to water stress to be the superior isolate of the three.