Effects of nitrogen levels on growth, photosynthesis, and nutrient interactions in sour orange seedlings grown in nutrient solution

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 (۲, ۴, ۸, ۱۶, and ۳۲ 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 (۴.۹۵ g), root length (۵۱.۵ cm), chlorophyll content (۸.۶ mg g⁻¹ FW), and photosynthetic efficiency (Fv/Fm = ۰.۷۳; PI = ۴.۲) occurred at ۱۶ mM N compared to ۲ mM N. In contrast, N deficiency (۲–۸ mM) reduced growth and photosynthetic performance, while N toxicity (۳۲ mM) decreased plant biomass by ۵۰%, impaired chlorophyll synthesis, and disrupted photosystem II efficiency (Fv/Fm = ۰.۵۵). Excessive N (۳۲ mM) altered nutrient homeostasis, increasing root Ca and K concentration by ۰.۸۲% and ۲.۴۹% 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 N۱۶ and N۳۲ 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 ۱۶ mM N optimizes sour orange growth.

کلیدواژه ها:

Nitrogen deficiency ، Nitrogen toxicity ، Nutrient imbalance ، Photosynthetic efficiency