Growth, Acetylene Reduction Activity, Nitrate Uptake and Nitrate Reductase Activity of Azolla caroliniana and Azolla pinnata at Varying Nitrate Levels

Abstract

The effect of varying nitrate levels (0—20 mM) was studied on the relative growth rate (RGR), acetylene reduction activity (ARA), nitrate uptake and nitrate reductase (NR) activity of A. caroliniana and A. pinnata. In both Azolla species, RGR was higher with 5 mM nitrate as compared to N-free medium whereas higher concentration of nitrate reduced the RGR. The significant inhibition of ARA was observed on 16th day after incubation with 5 mM nitrate, 12th day with 10 mM, 8th day with 15 mM and 4th day with 20 mM. The increasing nitrate levels resulted in increased nitrate uptake and NR activity in both the species. A. caroliniana recorded higher RGR and ARA whereas nitrate uptake and NR activity were higher in A. pinnata.