Abstract: Using NH₄⁺-N, NO₃^--N and CO(NH₂)₂ as nitrogen sources, the effect of nitrogen forms and the ratios on the plant size, biomass, root morphological characteristics, content and accumulation of elements in Juglans sigillata seedling was studied. The results showed that the nitrogen forms and the ratios had significant impact on seedling height, base diameter, root-shoot ratio, shoot and root biomass, root morphological trait, content and accumulation of elements in J. sigillata seedling. With the mixed supply of NH₄⁺-N and NO₃^--N at the ratio of 1∶1, the seedling height, base diameter, root-shoot ratio, biomass of the entire plant, shoot and root, root total surface area, average diameter, root tip number, content and accumulation of elements in J. sigillata seedling were all at the maximum compared with other treatments. With the only supply of CO(NH₂)₂, root total length and volume were the biggest, the biomass of the entire plant, shoot and root, the content and accumulation of elements in seedling were lower only than those with the mixed supply of NO₃^--N and NH₄⁺-N at the ratio of 1∶1. With the only supply of NO₃^--N, the seedling was short and small, the biomass of the entire plant, shoot and root, root morphological parameters were all the lowest, and the content and accumulation of elements in seedling were the least. With the only supply of NH₄⁺-N, most of the leaves in summer presented burning-shape necrosis, and the symptom was aggravated with increasing NH₄⁺-N ratio. Meanwhile the seedling was slender, the tissue was not fully developed, the fibrous root was short and most fibrous roots showed necrosis, the biomass, root-shoot ratio and root total length, surface area, volume, average diameter and root tip number were smaller, and the accumulation of elements was also lower. J. sigillata seedling had no obvious preference to NH₄⁺-N or NO₃^--N. The mixed supply of NO₃^--N and NH₄⁺-N at the ratio of 1∶1 was able to boost the growth and nutrients absorption of J. sigillata seedling. CO(NH₂)₂ was also good for growth and nutrients absorption of J. sigillata seedling.

Key words: Juglans sigillata, seedling, nitrogen form, growth, nutrients absorption