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 investigated. The gradual decreases in the growth and acetylene reduction activity (ARA) of the plants in pond water were due mainly to a phosphorus deficiency. In secondary effluent, ammonium was an important factor limiting growth and ARA. The ARA was inhibited by ammonium in the medium even at 0.1 mM, whereas the growth rate in up to 1 mM ammonium was comparable with that of plants grown without ammonium. Nitrite and volatile organic acids in culture media were very toxic to Azolla plants. In secondary effluent containing nitrite, the plants shed their roots, followed by the fragmentation of fronds, and eventually died.