Azolla pinnata redefines its importance in rice fields as it alleviates aluminum toxicity and low pH stress

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Monoculture of rice seedlings or Azolla pinnata was challenged with different aluminum stress conditions, and both species showed significantly reduced total biomass, chlorophyll, root, and leaf length. Mixed cultures showed no stress phenotypes and notably enhanced growth parameters under low and moderate aluminum stress (10 and 30 μM). Discretely, Azolla plants failed to survive when grown at >30 μM aluminum treatment (pH 4.75) but sustained well when grown with rice plants. Importantly, both species accumulated less aluminum and more root exudates in mixed cultures of Azolla and rice plants. Furthermore, expression of Sensitive To Proton rhizotoxicity1 (ApSTOP1 and OsART1) in both species declined significantly in mixed cultures than in monocultures. Ammonium transporter 1 (ApAMT1 and OsAMT1.1) expressed significantly more in heterogeneous cultures, indicating that ammonium transport is unaffected. Our observations conclude that aluminum accumulation and stress effects significantly decreased in heterogeneous cultures when compared with homogenous cultures.