The influence of algal biostimulator and nitrogen source on the phytochemical composition and biological properties of Corchorus olitorius leaves and stems

The present study aimed to evaluate the impact of different nitrogen sources combined with an algal biostimulant on the biochemical composition and biological activities of Corchorus olitorius (Mulukhiyah) grown under saline irrigation. A pot experiment was conducted during the summer season of 2023 at the Algal Biotechnology Unit, National Research Centre, Cairo, Egypt. Seeds were soaked in algal slurry and cultivated in sandy soil, irrigated with Pandorina sp. slurry (3846.4 ppm on average), and supplemented with an in situ algal biostimulator applied as a foliar spray (1.0 mL L^-1) in combination with nitrogen, phosphorus, and potassium (NPK) fertilization. Phytochemical analyses revealed that leaves consistently accumulated higher levels of sterols, terpenes, fatty acids, pigments, polyphenols, tannins, and flavonoids compared with stems. Among the three fertilization regimes, ammonium nitrate, in combination with the biostimulant, produced the highest concentrations of sterols (1.03% in leaves), terpenes (0.93%), fatty acids (3.05%), chlorophylls (4.16 mg/g), carotenoids (3.79 mg/g), polyphenols (252.76 mg/100 g), condensed tannins (101.10 μg/mL), and flavonoids (6.19 mg/g). HPLC profiling confirmed the presence of diverse phenolic and flavonoid compounds, including gallic acid, chlorogenic acid, caffeic acid, rutin, quercetin, and kaempferol, with leaves exhibiting a broader and higher profile than stems. In vitro biological assays demonstrated that ammonium nitrate-treated extracts exhibited superior antioxidant activity (total antioxidant capacity: 129.6 ± 2.3 mg GAE/g; DPPH scavenging IC₅₀: 41.8 ± 1.2 µg/mL), anti-Alzheimer activity (AChE inhibition: 67.4% at 200 µg/mL), anti-diabetic activity (α-amylase IC₅₀: 72.3 ± 1.5 µg/mL), and cytotoxic effects, particularly against Caco-2 cells (IC₅₀: 50.65 ± 2.84 µg/mL). Conversely, no significant enhancement was observed in anti-inflammatory and anti-arthritic properties, where all extracts showed comparable inhibition (~ 48-52%) relative to the standard drug diclofenac. Overall, the findings indicate that the combined application of ammonium nitrate fertilizer and algal biostimulant enhances the accumulation of bioactive phytochemicals in C. olitorius, which translates into improved pharmacological potential, particularly antioxidant and cytotoxic activities. These results support the use of optimized fertilization strategies for improving the nutraceutical and medicinal value of C. olitorius under saline conditions.