Limited data are available on the physiological responses of Citrus to nitrogen (N) deficiency. ‘Xuegan’ (Citrus sinensis (L.) Osbeck) and ‘Shantian pummelo’ (Citrus grandis (L.) Osbeck) seedlings were fertilized with nutrient solution at a N concentration of 0, 5, 10, 15 or 20 mM for 10 weeks. N deficiency decreased N uptake and N concentration in leaves, stems and roots and disturbed nutrient balance and homeostasis in plants, thus inhibiting plant growth, as well as reducing photosynthetic pigment levels and impairing thylakoid structure and photosynthetic electron transport chain (PETC) in leaves, hence lowering CO₂ assimilation. The imbalance of nutrients intensified N deficiency’s adverse impacts on biomass, PETC, CO₂ assimilation and biosynthesis of photosynthetic pigments. Citrus displayed adaptive responses to N deficiency, including (a) elevating the distributions of N and other elements in roots, as well as root dry weight (DW)/shoot DW ratio and root-surface-per-unit volume and (b) improving photosynthetic N use efficiency (PNUE). In general, N deficiency had less impact on biomass and photosynthetic pigment levels in C. grandis than in C. sinensis seedlings, demonstrating that the tolerance of C. grandis seedlings to N deficiency was slightly higher than that of C. sinensis seedlings, which might be related to the higher PNUE of the former.

中文翻译：

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柑橘对缺氮反应的生长、矿物质营养素、光合作用和相关生理参数

关于柑橘对氮 (N) 缺乏的生理反应的可用数据有限。用 0、5、10、15或 20 mM 的 N 浓度营养液对‘雪干’（Citrus sinensis (L.) Osbeck）和‘山田柚’（Citrus grandis (L.) Osbeck）幼苗施肥 10 周. 缺氮会降低叶、茎和根的氮吸收和氮浓度，扰乱植物的养分平衡和体内平衡，从而抑制植物生长，降低光合色素水平，损害叶中的类囊体结构和光合电子传递链（PETC），从而降低 CO ₂同化。养分失衡加剧了缺氮对生物量、PETC、CO ₂的不利影响光合色素的同化和生物合成。柑橘对 N 缺乏表现出适应性反应，包括 (a) 提高根中 N 和其他元素的分布，以及根干重 (DW)/地上部 DW 比和每单位根表面积和 (b) 改善光合氮利用效率（PNUE）。在一般情况下，缺氮有在生物量和光合色素水平的影响更小柚比山茶苗，表明公差柚苗氮素缺乏是略高于的山茶苗，这可能与前者较高的 PNUE 有关。