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Phosphorus Requirement of Azolla pinnata : Effects of Low Concentrations on Growth and Nitrogen Fixation
Author(s) -
Sah R. N.
Publication year - 1989
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1989.0011183x002900040042x
Subject(s) - azolla , biology , nitrogen fixation , zoology , phosphorus , dry weight , botany , anabaena , nitrogen , cyanobacteria , bacteria , chemistry , genetics , organic chemistry
There are conflicting reports about the critical P requirements for growth and N 2 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 μM 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 μM . 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.