Effects of different nitrogen treatments on the growth and nitrogen metabolism of Machilus thunbergii seedlings

All three nitrogen treatments significantly influenced both the growth and physiological indices of <i>M. thunbergii</i> seedlings. While generally enhancing the nitrogen metabolism and accumulation, improper selection of fertilizer types or excessive application rates elevated the tissue nitrogen concentration, inducing phytotoxic effects that ultimately inhibited seedling growth. In this research, sodium nitrate had the greatest toxic effect on <i>M. thunbergii</i> seedlings, followed by ammonium sulfate and urea. Among the nitrogen fertilizers tested, urea proved superior at an application rate of 3 g per plant for 3-year-old <i>M. thunbergii</i> seedlings.