Enhancing cabbage resilience against heavy metal stress through silicon amendments and melatonin: A depth investigation

•To determine the morphological and chemical alterations in cabbage plant under heavy metal stress.•To alleviate the heavy metal stress level through silica application.•To find out the optimum concentration of silica treatment under heavy metal stress. This study investigated the phytotoxic toxic effects of heavy metals and evaluated the ameliorative effects of exogenously applied silicon (Si) in cabbage. Three experiments were conducted to assess the morphological, physiological, and biochemical changes associated with heavy metal toxicity and the potential mitigation by Si. The threshold level of cabbage plants was determined in the first experiment using nickel (Ni), cadmium (Cd), and arsenic (As) as selected heavy metals. Significant reductions in growth attributes, such as plant biomass, leaf area, and root weight, were observed at all heavy metal concentrations. Physiological parameters, including photosynthetic rate, transpiration rate and stomatal conductance were also significantly reduced due to heavy metal toxicity. In the second experiment, foliar application of Si at different concentrations mitigated the negative impacts of heavy metals on plant growth and physiological attributes. Maximum mitigation was observed at Si concentrations of 2 mM and 3 mM. The third experiment confirmed the efficacy of Si at 2 mM in reducing heavy metal toxicity and improving physiological attributes. Si application significantly decreased the uptake of Cd, Ni, and As in cabbage plants. Chlorophyll contents and antioxidant enzyme activities indicated the positive impact of Si on growth and development under heavy metal stress. Heavy metals exhibited toxic effects on cabbage plants, but exogenous application of Si, particularly at 2 mM, effectively mitigated these effects and enhanced plant growth. Si application at 3mM exhibited the maximum reduction in Cd toxicity, leading to a 79% increase in fresh biomass. When Ni and Cd-stressed plants were treated with silicon at 2mM, there was maximum reduction in toxicity, resulting in a 75% and 71% increase in the photosynthetic rate. Maximum mitigation of Cd toxicity was achieved by applying silicon at 2mM, resulting in a 94% increase in stomatal conductance. Furthermore, under a-biotic stress cabbage increased the concentration of melatonin that help the plant to cope from stress. These findings demonstrate the potential of Si application as a strategy to alleviate heavy metal toxicity and improve the growth of cabbage