Introduction: The increasing contamination of water and soil resources by heavy metals, particularly arsenic, due to industrial activities and the discharge of polluted effluents, has raised serious concerns regarding agricultural productivity and food safety. Given the necessity of finding biological strategies to mitigate the toxic effects of such contaminants on crops, this study aimed to investigate the effect of selenium (sodium selenate) foliar application in alleviating the negative impacts of arsenic stress on fenugreek (Trigonella foenum-graecum L.) under controlled conditions.
Materials and Methods: A factorial experiment was conducted based on a completely randomized design with three replications at the University of Mohaghegh Ardabili in 2025. The soil was artificially contaminated with arsenic at four levels (0, 30, 60, and 90 mg/L) over a four-month period. Fenugreek seeds were then sown in the treated soils, and two weeks after germination, selenium foliar application was performed at four concentrations (0, 10, 20, and 40 µM) in three intervals of ten days. Morphological, physiological, and biochemical traits were measured following the treatments.
Results and Discussion: The results demonstrated that arsenic stress significantly reduced shoot dry weight (by 91.3%), root dry weight (by 92.3%), and leaf area (by 94.1%) compared to the control. In addition, relative water content (RWC) decreased by 17.9%, and electrolyte leakage increased by 65.2%, while catalase and peroxidase activities increased by approximately 316.7% and 231.8%, respectively. Photosynthetic pigments, including chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids, decreased by 15.7%, 1.3%, 13.1%, and 15.9%, respectively. The highest proline content (a 91.5% increase compared to the control) was recorded under the combined treatment of 90 mg/L arsenic and 40 µM selenium. Foliar application of selenium at 10 and 20 µM significantly moderated the adverse effects of arsenic stress. Under non-stress conditions, the 20 µM selenium treatment increased chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid content by 17.9%, 8.6%, 16.3%, and 25.3%, respectively, compared to the control. Furthermore, application of 20 µM selenium under 60 and 90 mg/L arsenic stress enhanced leaf RWC by 8.7% and 8.3%, respectively. In contrast, the 40 µM selenium concentration exhibited toxic effects. Overall, low concentrations of selenium improved fenugreek tolerance to arsenic stress by enhancing antioxidant capacity, membrane stability, and photosynthetic pigment content.
Conclusion: The overall findings indicate that arsenic stress had significant negative effects on the morphophysiological and biochemical characteristics of fenugreek. However, selenium application, particularly at optimal concentrations, effectively alleviated arsenic toxicity and improved plant performance. These findings highlight the high potential of selenium as an effective nutritional strategy for enhancing fenugreek tolerance to heavy metal stress and improving agricultural sustainability in contaminated environments