Influence of nitrogen speciation on Cd-induced toxicity in Landoltia punctata

Nitrogen (N) plays an important role in plant growth and developmental metabolic processes, research on nitrogen speciation regulating Cd accumulation in duckweed is still limited. In this study, the effects of three nitrogen sources (NH₄Cl, Ca(NO₃)₂ and NH₄NO₃) on the growth, Cd accumulation, and photosynthetic parameters of Landoltia punctata (L. punctata) were analyzed. The results showed that Cd enrichment in L. punctata was significantly reduced (p < 0.05) with different nitrogen treatments compared to the control (CK). Ammonium nitrogen (NH₄-N) is more conducive to the accumulation of Cd in L. punctata than nitrate nitrogen (NO₃-N). The sum of the cell wall components and soluble components of Cd in the NH₄-N treatment group was greater than that in the NO₃-N treatment group. The proportion of F_NaCl extracts in the NH₄-N treatment group was greater than in the NO₃-N treatment group. NO₃-N led to a greater reduction in photosynthetic pigment content than NH₄-N. Overall, applying different forms of nitrogen can alleviate Cd toxicity in L. punctata, and the detoxification effect of the NH₄-N treatment is stronger than that of NO₃-N treatment. This study will provide theoretical and practical support for the application of duckweed in Cd phytoremediation even in eutrophic aquatic environments.