Mean (± standard deviation) nitrogen concentration in the plants of the monocultures of <i>Azolla</i> (<i>A</i>. <i>filiculoides</i>), <i>Lemna</i> (<i>L</i>. <i>minor/gibba</i>) and <i>Ricciocarpus</i> (<i>R</i>. <i>natans</i>) in the four treatments at the end of the experiment.

<p>Different letters indicate significant differences (p<0.05) found through pairwise comparisons. Number of replicates is given between brackets below the bars.</p>