Alleviating cadmium toxicity in Pak Choi using Sargassum stolonifolium biomass: physio-biochemical, anatomical and radionuclide uptake responses

Abstract

Cadmium (Cd) accumulation in leafy vegetables from contaminated soils impairs growth and poses serious health risks. Thus, minimizing Cd uptake, mobility and improving growth of Brassica chinensis (Pak Choi) is essential for food safety. This study examined the effectiveness of Sargassum stolonifolium biomass (SSB) in reducing Cd toxicity and enhancing the physio-biochemical defense of B. chinensis. Seedlings of B. chinensis were exposed to 50 mg Cd with or without varying levels of SSB and categorized as T0 (control, no Cd), T1 (50 mg kg⁻¹ Cd), T2 (50 mg Cd + 25 g SSB), T3 (50 mg Cd + 50 g SSB), and T4 (50 mg Cd + 100 g SSB). Physiological, biochemical, defense-related parameters, and Cd immobilization were subsequently assessed. Bioactive compounds (total 25) of SSB significantly decreased Cd accumulation in the leaves, stems, and roots of B. chinensis. Compared with T1 plants, T4 treatment significantly enhanced chlorophyll a (3.35-fold), chlorophyll b (4.71-fold), carotenoid content (1.54-fold), and Fv/Fm by 5.43%. T4 treated seedlings also exhibited increased transpiration rate (2.00-fold), stomatal conductance (2.21-fold), internal CO₂ concentration (0.22-fold), and net photosynthetic rate (2.45-fold) whereas SSB subjunction to T4 lowered stress biomarker levels, strengthened plant defense mechanisms, and improved the physicochemical properties of Cd-stressed plants. Significant increases in RWC (51.06%), proline (26.33%), glutathione (96.06%), and amino acids accumulation were observed in T4 treated plants. GC–MS analysis identified enhanced accumulation of 41 volatile metabolites in Cd-exposed B. chinensis seedlings supplemented with SSB. SSB application promoted antioxidant activity, improved stomatal size and density, and reduced the accumulation of Cd and radioactive materials. This study concluded that S. stolonifolium biomass at 100 g kg⁻¹ soil effectively alleviated Cd stress; however, its wider application is limited by species availability and insufficient understanding of its mechanisms of action.