INFLUENCE OF DOMESTIC SEWAGE ON GROWTH AND NITROGEN-FIXATION OF AZOLLA-PINNATA R BR

Biomass production of Azolla pinnata R. Br., cultured in sewage effluents under full sunlight, correlated closely with the changes of orthophosphate phosphorus (P) in the medium: it was highest (13.18 g m-2) in August as opposed to 6.34 g m-2 in January, though the environmental influence was also remarkable. Phosphorus contents in different media, particularly in one receiving a higher quantity of sewage effluents, gradually increased to 20.30 .mu.g l-1 in January, reaching a maximum in May (37.60 .mu.g l-1), followed by a gradual decline with a further rise in August (32.70 .mu.g l-1). The seasonal variation in phosphorus content of the medium was closely associated with the carbon, phosphorus and nitrogen contents of plant tissue, as well as the heterocyst frequency of the symbiont, and nitrogen contents of plant tissue, as well as the heterocyst frequency of the symbiont, Anabaena azollae Strasb. The respective increases in nitrogen, carbon and phosphorus contents of plant tissue in mg 1-1 during August were 39.80, 280.00 and 2.20, compared with values of 28.20, 245.00 and 1.50 during January, while the heterocyst frequencies were 15.96 and 10.92, respectively.