Response of Schefflera actinophylla Plants Grown under Drought to Soil Compost Addition and Foliar Application of Melatonin

The provision of irrigation water has become crucial, especially for ornamental plants, due to Egypt's demanding water conditions. The use of inexpensive soil amendments i.e., compost and the application of a newly discovered molecule "melatonin" can mitigate the negative effects of water scarcity. Therefore, this study aimed to evaluate the efficacy of combining compost with melatonin in alleviating the adverse effects of water deficit on Schefflera actinophylla L plants. Different irrigation regimes i.e., irrigation every 5 (I 1 ), 7 (I 2 ) and 10 (I 3 ) days were evaluated as the main factor. The final composition of the pots, consisting of compost and sand, with options including 1:3 compost: sand mixtures v/v (C 1 ), 1:1 compost: sand mixtures v/v (C 2 ) and 3:1 compost: sand mixtures v/v (C 3 ) was investigated as a secondary factor. In addition, the application of melatonin by spraying at concentrations of zero (F 1 ) and 100 μM (F 2 ) was investigated as a tertiary factor. Plant performance decreased with increasing irrigation intervals. Furthermore, plants grown in pots containing 75%compost+25% sand (C 3 ) showed the best performance followed by the C 2 treatment and finally the C 1 treatment. Moreover, the application of melatonin led to an increase in all the growth and chemical characteristics studied, as well as in the levels of antioxidant, except for malondialdehyde, which decreased compared to the untreated plants. On another note, the plant performance was better under combined treatments of I 2 xC 2 (or C 3 ) xF 2 than that under combined treatments of I 1 xC 1 xF 1 . Finally, these results confirm the potential role of compost and melatonin in mitigating the adverse effects of water deficit.