Phosphorus Requirement of Azolla pinnata: Effects of Low Concentrations on Growth and Nitrogen Fixation
There are conflicting reports about the critical P requirements for growth and N2 fixation of Azolla pinnata-Anabaena azollae association (azolla). This study was conducted to determine critical concentrations of media P and tissue P for optimum growth and N2 fixation of azolla. Continuous flow-through experiments using media-P levels ranging from 0 to 500 μM were conducted in a greenhouse. There were no differences in growth and N 2 fixation of azolla grown at media-P concentrations between 0.5 and 500 μM. Azolla initially high in tissue P (13 to 15 g P kg-I dry wt.) grew in the Pfreemedium at the optimum rate for about I0 d. For the optimum growth of azolla, media P between 0 and 0.5 ~M and about 1.0 g tissue P kg-1 dry wt. appeared to be the critical concentration. The critical medium-P concentration was significantly lower than the reported value, 2 ~M. Nitrogen fixation correlated with growth, but tissue-N and P concentrations did not. Increasing media-P concentrations decreased P utilization efficiency. Results suggest that the difference between deficient and sufficient media-P and tissue-P levels may be very narrow.
Copyright © 1989.