Melatonin-mediated adaptation of spinach (Spinacia oleracea L.) in acidic soil

Abstract

Soil acidity is a widespread and critical factor contributing to soil degradation. Melatonin (MT) as a protective biostimulant, plays a crucial role in plant growth under harsh environments. However, the role of MT in plant adaptation to acidic soil remains elusive. Hence, here we tested the effects of exogenous MT on the adaptation of spinach (Spinacia oleracea L.) crop to acidic soil (pH 4.0). Initially, a series of MT concentrations (0, 25, 50, 100, and 200 μM) were tested to evaluate the seed germination and growth attributes of spinach under low pH levels. Among the doses, 100 μM MT showed better results in terms of germination percentage and biomass accumulation, which was then selected for further experiments. Results showed that exogenous MT significantly increased plant adaptation to acidic soil as evidenced by increased photosynthesis rate and biomass accumulation with enhanced total antioxidant capacity, DPPH free radical scavenging, phenol, flavonoid, and glutathione contents compared with soil acidity treatment alone. Moreover, MT alleviated oxidative stress indices such as electrolyte leakage and malondialdehyde in acid-stressed plants, suggesting an effective strategy of adaptation. Furthermore, MT-treated plants exhibited higher macro and micronutrient accumulation along with higher vitamin B complex, vitamin C, and protein content, leading to an increased nutritional quality and yield compared to control. Therefore, the study concludes that the application of MT at 100 μM could be a sustainable alternative approach to adapt spinach farming in acidic soil.