Effect of phosphorus and nitrogen on growth, chlorophyll, amino nitrogen, soluble sugar contents and algal heterocysts of water fernAzolla pinnata

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Abstract
The P uptake inAzolla pinnata in mineral medium increased linearly with increasing phosphate doses and optimum growth and chlorophyll content of fern were recorded at 1.2 mM of K2HPO4. The higher doses of phosphate reduced growth and chlorophyll, but an increase in soluble sugar and amino nitrogen was noticed. Addition of combined nitrogen sources decreased the fern growth, soluble sugar, chlorophyll and heterocyst frequency but amino nitrogen was comparatively higher. The growth and chlorophyll content were always high when the fern was grown in the absence of added nitrogen sources; this supports the thesis about the specific importance of symbiosis for the nutrition of fern with nitrogen which cannot be replaced by mineral compounds.