Research in Plant Metabolites

Research in Plant Metabolites

Effect of Fulvic Acid on the Growth and Biochemical Characteristics of Red Lettuce under Chromium Stress

Document Type : Original Article

Authors
Rasoul Azarmi 1
Maryam yosefzadeh Eisalou 2
Zahra Majnouni Heris 2
behrooz esmailpour 2
sharareh Asghari 3
1 Department of Horticultural Sciences, Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili , Ardabil, Iran.
2 Department of Horticultural Sciences Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabil, Iran.
3 Department of Education, District 2, Ardabil.
10.22034/jrpsm.2026.593440.1127
Abstract
AbstractBackground & Objective: Chromium is a heavy metal that has detrimental effects on plant growth and food chain health. Fulvic acid, as an organic compound and growth stimulant, plays a role in enhancing plant tolerance to abiotic stresses. The present study was conducted to investigate the effects of fulvic acid application on inducing tolerance in red lettuce (Lactuca sativa cv. Little Gem) under chromium stress.
Materials and methods: To investigate the interactive effects of chromium stress and fulvic acid application on morphophysiological and biochemical traits of red lettuce, a factorial experiment was conducted based on a completely randomized design (CRD) with four replications under controlled hydroponic conditions at the research greenhouse of the University of Mohaghegh Ardabili, Iran. The experimental treatments comprised three levels of chromium stress (0, 3, and 15 mg L⁻¹, supplied as K₂Cr₂O₇) and two concentrations of fulvic acid (0 and 0.05 g L⁻¹), which were applied to the nutrient solution throughout the growth period. Plants were cultivated in a modified Hoagland solution with continuous aeration and maintained under a 16/8 h light/dark photoperiod at 25 ± 2 °C. At the end of the vegetative stage (45 days after transplanting), various growth, physiological, and biochemical parameters were assessed. The measured traits included shoot and root dry weight (after oven-drying at 70 °C for 48 h), total chlorophyll content (extracted in 80% acetone and measured spectrophotometrically), leaf macronutrient concentrations (nitrogen, phosphorus, and potassium using standard Kjeldahl, colorimetric, and flame photometric methods, respectively), total soluble sugars (phenol–sulfuric acid method), ascorbate peroxidase (APX) activity (spectrophotometric monitoring of ascorbate oxidation at 290 nm), hydrogen peroxide (H₂O₂) content (titanium sulfate method), chromium accumulation in leaf tissues (after acid digestion using atomic absorption spectrophotometry), electrolyte leakage (as an indicator of membrane integrity), stomatal conductance (using a portable porometer), and anthocyanin content (pH-differential method). All chemical analyses were performed in triplicate to ensure data accuracy and reproducibility.
Results: The obtained results revealed that increasing chromium concentration in the nutrient solution exerted a dose-dependent inhibitory effect on most of the measured growth parameters. Compared to the chromium-free control treatment, application of 15 mg L⁻¹ Cr significantly decreased shoot dry weight by 12.73%, root dry weight by 15%, and leaf nitrogen content by 17.7%, indicating severe impairments in nitrogen assimilation and biomass partitioning. In contrast, the same chromium level induced substantial increases in soluble sugar content (12.5%), peroxidase enzyme activity (129%), and hydrogen peroxide accumulation (29%), reflecting the activation of stress-responsive osmoprotective and antioxidative mechanisms. Notably, supplementation with fulvic acid at 0.05 g L⁻¹ effectively counteracted these adverse effects, leading to marked improvements in growth traits, total chlorophyll content, and leaf nitrogen status, while concurrently reducing chromium accumulation in leaf tissues. A dose-dependent increase in leaf chromium concentration was observed in plants not receiving fulvic acid; however, FA application significantly decreased leaf Cr content, presumably through metal chelation and restricted root-to-shoot translocation. Furthermore, electrolyte leakage—a reliable indicator of oxidative membrane damage—exhibited a 23% reduction in fulvic acid-treated plants under severe chromium stress (15 mg L⁻¹), suggesting enhanced membrane stability and reduced lipid peroxidation. Stomatal conductance and anthocyanin content, both of which declined progressively with increasing Cr levels, were significantly restored upon fulvic acid application, indicating improved gas exchange capacity and secondary metabolite production under stress conditions. Collectively, these findings demonstrate that fulvic acid mitigates chromium phytotoxicity through a multi-mechanistic approach, involving oxidative stress attenuation, membrane integrity preservation, photosynthetic pigment enhancement, and reduced heavy metal mobilization toward above-ground organs.
Conclusion: In summary, the present study provides compelling evidence that chromium stress, particularly at higher concentrations, imposes substantial negative impacts on the morphophysiological, biochemical, and nutritional quality traits of red lettuce in hydroponic cultivation. Nevertheless, exogenous application of fulvic acid at an optimized concentration proved highly effective in alleviating chromium-induced damages by reinforcing the plant's antioxidative defense system, maintaining cellular membrane functionality, and restricting chromium translocation to edible portions. These promising results suggest that fulvic acid can be introduced as a sustainable, low-cost, and environmentally compatible biostimulant for improving the resilience of leafy vegetables against heavy metal contamination in controlled-environment agriculture systems. However, further field-based studies across different soil types, climatic conditions, and crop species are recommended to validate its practical applicability and to establish dose-response relationships for commercial recommendations.
Keywords
Keywords: Humic substances
Hydroponics
Chromium
Lettuce
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