The effects of nitrogen as NO<inf>3</inf>^-and NH<inf>4</inf>⁺on the growth and symbiont (Anabaena azollae) of Azolla pinnata R. Brown

Abstract

The growth, morphology, and symbiont (Anabaena azollae) of Azolla pinnata R. Brown were investigated under different external N-supply regimes to inform the plant's potential in wastewater treatment. Azolla pinnata plants were supplied with nitrogen as NO3-or NH4+at four different concentrations (0, 0.5, 1, and 5 mM) and incubated in a greenhouse for 14 days. The relative growth rates of NO3--fed plants were not significantly different between treatments, but decreased significantly at the highest NH4+concentration. Moreover, the NO3-concentration did not affect root number. The highest NH4+concentration (5 mM) decreased both the root length and number of symbionts (Anabaena azollae) in the mature leaves of Azolla pinnata. Because Azolla pinnata continued to grow well with supplied NO3-and NH4+, and retained their ability to absorb nitrogen, they offer potential for treating wastewater, except at the highest NH4+concentration, which led to toxicity.