Melatonin upregulates photosynthesis, carbohydrate and nitrogen metabolism, and antioxidant system under aluminum stress: a sustainable path to higher strawberry yield and quality

Aluminum (Al) toxicity exhibits a challenge for growing strawberries (<i>Fragaria</i> x <i>ananassa</i> Duch), impacting their growth and nutritional value. Considerably in this study, we explored how melatonin, an endogenous plant hormone, can help alleviate Al stress in strawberry plants. The current research examined the effects of foliar spraying melatonin (0,50, and 100 ppm) on growth indicators, photosynthetic pigment levels, carbon and nitrogen assimilation, oxidative stress markers, and fruit quality attributes under Al stress (100 µM) in a controlled pot experiment conducted in a greenhouse. The results revealed that exposure to Al stress significantly reduced the adequate growth, as well as the yield and quality of fruits. Melatonin application improved plant growth parameters, especially at a concentration of 100 ppm, enhancing the levels of photosynthetic pigments and boosting carbohydrate and nitrogen metabolism. Moreover, melatonin played a role in reducing stress markers while increasing enzymatic antioxidant activities (catalase, superoxide dismutase, ascorbate peroxidase, glutathione peroxide, glutathione-S-transferase, and phenylalanine ammonia-lyase) and secondary metabolites (proline, ascorbic acid, flavonoids, reduced glutathione, and phytochelatins), while decreasing polyphenol oxidase activity as well as phenolics content, implying a role in ROS scavenging. The results underscore the promise of melatonin as a method to enhance the ability of strawberries to withstand Al toxicity and promote friendly agricultural practices in polluted soils.