Abstract: To understand the effects of salinity on nitrogen and phosphorus uptake of Suaeda salsa and Phragmites australis, the uptake characteristics of NH₄⁺-N and H₂PO₄^--P of both species under salt stress were investigated by depletion method. Two levels of NaCl (S. salsa: 0 and 1.5%, P. australis: 0 and 1%), five levels of NH₄⁺-N (0.25, 1, 5, 10, and 15 mmol·L^-1), and six levels of H₂PO₄^--P (0.25, 0.5, 1, 2, 5, and 10 mmol·L^-1) were established. The concentration of the solution was measured at 0, 1, 2, 3, 5, 7, 9 and 12 h to obtain the uptake rate and kinetic characteristics of nitrogen and phosphorus by S. salsa and P. australis. The results showed that the uptake of NH₄⁺-N and H₂PO₄^--P by S. salsa fitted the Michaelis-Menten equation. Uptake kinetics of NH₄⁺-N by S. salsa showed a linear response at 1.5% NaCl, but saturated at 0 NaCl. 1.5% NaCl inhibited the uptake of NH₄⁺-N and H₂PO₄^--P by S. salsa. Compared to the 0 NaCl treatment, the maximum absorption rate (V_max) and the Michaelis constant value (K_m) of NH₄⁺-N uptake by S. salsa increased by 157.43% and 1542.99% at 1.5% NaCl, respectively, while the flow rate of NH₄⁺-N in root (α) decreased by 84.35%. Compared to the 0 NaCl treatment, the V_max and α of H₂PO₄^--P decreased by 10.18% and 27.84% at 1.5 % NaCl, and K_m increased by 23.92%. For P. australis, the uptake kinetics of NH₄⁺-N and H₂PO₄^--P could be described by Michaelis-Menten equation. The absorption curves were consistent with the saturation kinetics characteristics. 1% NaCl promoted the uptake of NH₄⁺-N and H₂PO₄^--P. Compared to the 0 NaCl treatment, the V_max of NH₄⁺-N uptake by P. australis increased by 16.65%, K_m decreased by 53.02%, α increased by 147.02% at 1% NaCl. The V_max of H₂PO₄^--P uptake increased by 166.77%, K_m decreased by 28.35%, and α increased by 278.57% at 1% NaCl. Collectively, our findings demonstrate that the uptake characteristics of nitrogen and phosphorus by S. salsa and P. australis under salt stress differ significantly. This discrepancy may be attributed to their distinct nutrient acquisition strategies. Our results provide a theoretical foundation for investigating vegetation restoration and purification functions in coastal wetlands.

Key words: Suaeda salsa, Phragmites australis, kinetic characteristics, nitrogen, phosphorus, salinity