Phytoremediation potential of Azolla in removal of nitrogen from wastewater has been promising. However, little is known about the response of Azolla to high concentrations of nitrogen. In this study, the responses of four Azolla species to different concentrations of total nitrogen ranging from 0 to 180 mg L⁻¹ were examined. The responses varied among different species, and the high nitrogen-tolerant species A. caroliniana and A. microphylla could remove nitrogen from aqueous solutions with higher efficiencies. We further performed transcriptome analysis to explore the molecular mechanism underlying the response to high nitrogen stress in Azolla. RNA-seq analysis revealed a synergistic regulatory network of differentially expressed genes (DEGs) involved in nitrogen transport and metabolism in A. microphylla, mainly in the roots. Under high nitrogen treatment, the DEGs encoding nitrate transporters or nitrate transporter 1/peptide transporters (NRTs/NPFs), ammonium transporters (AMTs), nitrate reductase (NIA), nitrite reductase (NIR) and glutamine synthetases/glutamate synthases (GSs/GOGATs) were down-regulated, and the DEGs encoding glutamate dehydrogenases (GDHs) were up-regulated, suggesting that A. microphylla possessed high tolerance against excess nitrogen through down-regulation of nitrate and ammonium uptake and fine regulation of nitrogen assimilation in the roots. Our results provided a theoretical foundation for better utilization of Azolla for wastewater treatment.

满江红在去除废水中氮方面的植物修复潜力一直很有前景。然而，关于满江红对高浓度氮的反应知之甚少。在这项研究中，研究了四种满江红对 0 到 180 mg L ^-1的不同浓度总氮的反应。不同物种的反应不同，高耐氮物种A. caroliniana和A. microphylla可以更高效率地从水溶液中去除氮。我们进一步进行了转录组分析，以探索满江红响应高氮胁迫的分子机制. RNA-seq 分析揭示了差异表达基因 (DEGs) 的协同调控网络，这些基因参与了小叶小叶植物的氮转运和代谢，主要存在于根部。在高氮处理下，编码硝酸盐转运蛋白或硝酸盐转运蛋白 1/肽转运蛋白 (NRTs/NPFs)、铵转运蛋白 (AMTs)、硝酸盐还原酶 (NIA)、亚硝酸盐还原酶 (NIR) 和谷氨酰胺合成酶/谷氨酸合成酶 (GSs/GOGATs) 的 DEGs ) 被下调，并且编码谷氨酸脱氢酶 (GDH) 的 DEGs 被上调，表明A. microphylla通过下调硝酸盐和铵的吸收以及对根中氮同化的精细调节，对过量氮具有高耐受性。我们的研究结果为更好地利用满江红处理废水提供了理论基础。