Plant Nutrition
Farnaz Kargar; Abbas Mirsoleimani; Mahdi Najafi-Ghiri
Abstract
Purpose: Nitrogen (N) plays a crucial role in citrus growth, but its deficiency or excess can disrupt nutrient balance and physiological functions in plant. This study investigated how varying N levels (2, 4, 8, 16, and 32 mM) affect growth, photosynthesis, root morphology and nutrient interactions in ...
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Purpose: Nitrogen (N) plays a crucial role in citrus growth, but its deficiency or excess can disrupt nutrient balance and physiological functions in plant. This study investigated how varying N levels (2, 4, 8, 16, and 32 mM) affect growth, photosynthesis, root morphology and nutrient interactions in sour orange (Citrus aurantium L.) seedlings. Research Method: Seedlings were grown in nutrient solutions with different N concentrations. Biomass, photosynthetic efficiency (Fv/Fm, PI), chlorophyll content, nutrient uptake, and nitrate reductase activity were analyzed. Findings: Maximum and significant plant dry weight (4.95 g), root length (51.5 cm), chlorophyll content (8.6 mg g⁻¹ FW), and photosynthetic efficiency (Fv/Fm = 0.73; PI = 4.2) occurred at 16 mM N compared to 2 mM N. In contrast, N deficiency (2–8 mM) reduced growth and photosynthetic performance, while N toxicity (32 mM) decreased plant biomass by 50%, impaired chlorophyll synthesis, and disrupted photosystem II efficiency (Fv/Fm = 0.55). Excessive N (32 mM) altered nutrient homeostasis, increasing root Ca and K concentration by 0.82% and 2.49% respectively but reducing their translocation to shoots, elevating the Ca/K ratio a key indicator of K deficiency risk in calcareous soils. Nitrate reductase activity declined under toxicity, reflecting suppressed N assimilation. Root N/Ca ratio decreased with increasing in N concentration and Ca/K ratio of root in N16 and N32 treatments was higher than that in other N treatments. Phenolic compounds accumulated in roots under high N, suggesting oxidative stress mitigation. Research limitations: No limitations were found. Originality/Value: Excessive N disrupts nutrient balance, photosynthetic inhibition, and growth suppression while 16 mM N optimizes sour orange growth.
