Effect of leaf positions on the concentrations of some micronutrients, antinutrients and toxic substances in Hibiscus sabdariffa at vegetative phase

The leaf age (which is linked to position on mother - plant) influenced the accumulation of nutrients and toxic substances by the leaves on plants. It is against this background that this study was carried out in pot experiment to examine the effect of leaf position on the levels of antinutrient (soluble and total oxalates), toxic substances (cyanide and nitrate) and some micronutrients viz; β-carotene (provitamin A), vitamin C and mineral elements (Fe, Mg, Cu, Zn, Ca Na and K) at vegetative phase of Hibiscus sabdariffa grown in nitrogen and non – nitrogen treated soil. The leaves of Hibiscus sabdariffa were harvested and analysed at three different leaf locations, namely; basal, middle and upper positions. The results obtained showed that the concentrations of cyanide and nitrate were generally higher in older leaves than younger ones. The soluble and total oxalate contents in the vegetable increased with leaf age. Vitamin C content was concentrated more in the middle leaf region compared to basal and upper leaf positions in the vegetable.The β-carotene concentration was significantly (p < 0.05) highest in middle leaves, closely followed by upper leaves and least in the basal leaves. Levels of Fe in the basal and middle leaves were not significantly different from each other, but the two leaf positions had significant (p < 0.05) higher amount of the mineral than upper leaves irrespective of the soil nitrogen levels.The concentrations Ca, Cu and Na were significantly higher in the basal leaf region compared to middle and upper leaf locations in Hibiscus sabdariffa except that no significant variation in Cu content was observed between basal and middle when nitrogen was applied. While leaf position had no significant effect on the concentrations of Mg and Zn in Hibiscus sabdariffa, the concentration of K was significantly higher in the upper leaves than the middle and basal leaves in control and nitrogen applied. The study concludes that the plant toxins are concentrated more in the older leaves than the younger ones in Hibiscus sabdariffa at vegetative phase.

Author(s): Amanabo Musa

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