THE GROWTH AND NITROGEN-FIXATION OF AZOLLA-FILICULOIDES LAM IN POLLUTED WATER

The growth and nitrogen fixation of Azolla filiculoides Lam. cultured in water of a polluted pond and two types of secondary effluent were i nvestigated. The gradual decreases in the growth and acetylene reducti on activity (ARA) of the plants in pond water were due mainly to a pho sphorus deficiency. In secondary effluent, ammonium was an important f actor limiting growth and ARA. The ARA was inhibited by ammonium in th e medium even at 0.1 mM, whereas the growth rate in up to 1 mM ammoniu m was comparable with that of plants grown without ammonium. Nitrite a nd volatile organic acids in culture media were very toxic to Azolla p lants. In secondary effluent containing nitrite, the plants shed their roots, followed by the fragmentation of fronds, and eventually died.