Drought is a limiting factor to forest regeneration and restoration, which is likely to increase in intensity and duration under future climates. Nitrogen (N) nutrition is related to drought-resistance mechanisms in trees. However, the influence of chemical N form (inorganic and organic N) on physiological traits related to drought resistance has been sparsely studied in conifer seedlings. We investigated the effect of N forms on morpho-physiological traits of Pinus ponderosa Dougl. ex Laws. seedlings and subsequent influences in drought tolerance and acclimation. One-year-old seedlings were fertilized during 10 weeks at 9 mM N with different N forms [either NH₄⁺, NO₃⁻ or organic N (amino acids mixture)] in their second year of growth. After fertilization, we measured traits associated with intrinsic drought tolerance (shoot water relations, osmotic regulation, photosynthesis and cell membrane stability). Seedlings were then subjected to an 8-week drought period at varying drought intensities to evaluate plant acclimation mechanisms. We demonstrated that P. ponderosa seedlings could efficiently use amino acids as a primary N source, showing similar performance to those grown with inorganic N forms. Nitrogen form influenced mainly drought-acclimation mechanisms rather than intrinsic drought tolerance. Osmotic potential at saturation (Ψ_πsat) was marginally affected by N form, and a significant relationship between proline concentration in needles and Ψ_πsat was found. During acclimation, seedlings fertilized with organic N minimized needle senescence, retained more nutrients in the oldest needles, had maximum increments in proline concentration and hastened the development of water-use efficiency mechanisms compared with those fertilized with inorganic N sources. Our results suggest an improved physiological drought acclimation of organic N-fertilized seedlings.

中文翻译：

---

黄松幼苗的耐旱性和适应性：氮形态的影响。

干旱是森林再生和恢复的限制因素，在未来的气候下，干旱的强度和持续时间可能会增加。氮营养与树木的抗旱机制有关。然而，已经在针叶树幼苗中稀疏研究了化学氮形态（无机和有机氮）对与抗旱性相关的生理特性的影响。我们调查了氮素形态对黄松道格拉形态生理特性的影响。前法律。幼苗及其后对耐旱性和适应性的影响。一岁的幼苗期间10周为9mm n，其中不同的氮形态[受精或者NH ₄ ⁺，NO ₃ ^-或有机N（氨基酸混合物）]。施肥后，我们测量了与内在耐旱性相关的性状（与水的关系，渗透调节，光合作用和细胞膜稳定性）。然后使幼苗经受不同干旱强度的8周干旱期，以评估植物的驯化机制。我们证明了美国黄杨幼苗可以有效地利用氨基酸作为主要的氮源，显示出与以无机氮形式生长的相似的性能。氮形态主要影响干旱适应机制，而不是固有的干旱耐受性。饱和时的渗透势（_Ψπsat）受N形态的影响很小，并且发现针中脯氨酸浓度与_Ψsat之间存在显着关系。在适应过程中，与无机氮源施肥相比，用有机​​氮肥施肥的幼苗可使针叶衰老最小化，在最老的针叶中保留更多的养分，脯氨酸浓度的增加最大，并加快了水分利用效率机制的发展。我们的结果表明有机氮肥幼苗的生理干旱适应性得到了改善。