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 (NH ₄ Cl, Ca(NO ₃ ) ₂ and NH ₄ NO ₃ ) 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 (NH ₄ -N) is more conducive to the accumulation of Cd in L. punctata than nitrate nitrogen (NO ₃ -N). The sum of the cell wall components and soluble components of Cd in the NH ₄ -N treatment group was greater than that in the NO ₃ -N treatment group. The proportion of F _NaCl extracts in the NH ₄ -N treatment group was greater than in the NO ₃ -N treatment group. NO ₃ -N led to a greater reduction in photosynthetic pigment content than NH ₄ -N. Overall, applying different forms of nitrogen can alleviate Cd toxicity in L. punctata , and the detoxification effect of the NH ₄ -N treatment is stronger than that of NO ₃ -N treatment. This study will provide theoretical and practical support for the application of duckweed in Cd phytoremediation even in eutrophic aquatic environments.