Effects of nitrogen and phosphorus addition on the stoichiometric characteristics of nitrogen, phosphorus, and potassium in Cinnamomum camphora container seedlings

To explore the effects of nitrogen (N) and phosphorus (P) addition on the stoichiometric characteristics of nutrient elements (N, P, K) in container-grown Cinnamomum camphora seedlings, one-year-old container-grown Cinnamomum camphora seedlings were used as experimental materials. An exponential fertilization method was adopted, with fertilization treatments including low N (N1), medium N (N2), high N (N3), P alone (P), low N+P (N1P), medium N+P (N2P), and high N+P (N3P), using no fertilization as the control (CK). After the seedlings ceased growth, the biomass and stoichiometric characteristics of nutrient elements (N, P, K) in roots, stems, and leaves were determined.The results showed that the root biomass reached the maximum value of 1.857 g/plant under the P-only treatment, while the stem biomass, leaf biomass, and total biomass under N3 were significantly higher than those under other treatments. The root N contents of container-grown Cinnamomum camphora seedlings under N3, N2P, and N3P treatments were significantly higher than those under other treatments, being 23.83 mg/g, 24.712 mg/g, and 24.876 mg/g, respectively. N2P was the treatment with the highest stem N content (15.035 mg/g). In leaves, except for the P-only treatment, the N contents of other treatments were significantly higher than that of CK, among which N3 and N2P treatments had the highest leaf N contents.Applying P alone significantly increased the P content in various organs of container-grown Cinnamomum camphora seedlings, showing a significant difference from CK (P<0.05), while applying N alone and combined N-P fertilization had little effect on the P content in various organs of the seedlings. Combined N-P fertilization significantly increased the leaf N/P ratio of container-grown Cinnamomum camphora seedlings, among which the leaf N/P ratio under N3P treatment was significantly higher than that under other treatments (4.67). In roots, the treatments with higher N/P ratios were N2P and N3P, being 6.18 and 6.16, respectively. N2P was the treatment with the highest stem N/P ratio (4.27). Overall, N2P and N3P treatments were more conducive to increasing the N/P ratios in roots, stems, and leaves of container-grown Cinnamomum camphora seedlings.Fertilization had no obvious effect on increasing the K content in the underground parts of container-grown Cinnamomum camphora seedlings, and the effect was mainly concentrated in the aboveground parts, especially leaves. Moreover, combined N-P fertilization had the greatest promoting effect on the leaf K content of container-grown Cinnamomum camphora seedlings. Under N2, N3, and N2P treatments, N/K>2.1 and K/P<3.4 were satisfied, indicating that the roots of container-grown Cinnamomum camphora seedlings were limited by K.Therefore, the limiting factor for the growth of container-grown Cinnamomum camphora seedlings is N limitation. Applying N alone or combined N-P fertilization can significantly increase seedling biomass, change the N/P ratios in various organs, and alleviate N limitation.