Nitrogen form plays an important role in the growth of moso bamboo ( Phyllostachys edulis) seedlings

Background: This study aimed to gain an understanding of the growth response of Phyllostachys edulis (moso bamboo) seedlings to nitrogen (N) and potassium (K) to benefit nutrient management practices and the design of proper fertilizer in nursery cultivation.

Methods: An orthogonal array L₈(4×2⁴) was used to study the effects of N forms (NH₄ ⁺, NO₃ ^-), N concentrations (8, 32 mmol/L), and K⁺concentrations (0, 0.5, 1.5, 3 mmol/L) on seedling height, leaf number, chlorophyll content (SPAD value), biomass, root systems, and N content of P. edulis seedlings. Plants were grown in vermiculite under controlled greenhouse conditions.

Results: Our study showed that N form played a significant role in the overall performance of P. edulis seedlings, followed by the effect of N and K⁺ concentrations. Among the N forms, NH₄ ⁺ significantly improved the growth of P. edulis seedlings compared with NO₃ ^-. Seedling height, leaf number, chlorophyll SPAD value, biomass, and root system architecture (root length, root surface area, root volume, and root tips) were greater with 8 mmol/L of NH₄ ⁺ treatments than with 32 mmol/L of NH₄ ⁺treatments, whereas root diameter and N content of P. edulis seedlings were higher with 32 mmol/L of NH₄ ⁺ than with 8 mmol/L of NH₄ ⁺. K displayed inconsistent effects on the growth of P. edulis seedlings. Specifically, seedling height, leaf number, biomass and root volume increased when the K⁺ concentration was increased from 0 to 0.5 mmol/L, followed by a decrease when the K⁺ concentration was further increased from 0.5 to 3 mmol/L. Root average diameter of the seedlings was the highest with a K⁺ concentration of 1.5 mmol/L, and K had some inhibitory effects on the chlorophyll SPAD value of the seedlings. P. edulis seedlings performed well with 8 mmol/L NH₄ ⁺and further tolerated a higher concentration of both NH₄ ⁺ and NO₃ ^-, although excessive N could inhibit seedling growth. A lower concertation of K (≤ 0.5 mmol/L) promoted seedling growth and increasing K⁺ concentration in the nutrient solution did not alleviate the inhibitory effect of high N on the growth of P. edulis seedlings. Therefore, NH₄ ⁺nitrogen as the main form of N fertilizer, together with a low concertation of K⁺, should be supplied in the cultivation and nutrient management practices of moso bamboo.

Keywords: Ammonium; Growth response; Nitrate; Nitrogen concentration; Nitrogen form; Phyllostachys edulis; Potassium.