Synergistic Biochar and Mycorrhizal Fungi Application Alleviates Cadmium Toxicity and Salinity Stress by Enhancing Soil Functioning and Tomato Productivity

Abstract

Tomato production is increasingly constrained by cadmium (Cd) contamination and abiotic stresses, which impair plant growth, fruit quality, and food safety. Innovative and eco-friendly strategies are therefore needed to mitigate these constraints. Biochar and mycorrhizal fungi, applied individually or synergistically, have the potential to improve soil biochemical properties, reduce metal bioavailability and toxicity, and enhance tomato growth and fruit quality under stress conditions. This study evaluated the synergistic effects of biochar (0, 1%, and 2% w/w) and mycorrhizal fungi on soil biochemical functioning, Cd bioavailability, and tomato growth in saline soil. The combined application of mycorrhizal fungi and biochar at 2% (w/w) significantly increased soil respiration and phosphatase, nitrogenase, and dehydrogenase activities by 140%, 127%, 330%, and 130%, respectively, while reducing soil electrical conductivity and available Cd concentrations by 29.9% and 59%, respectively. This treatment also markedly decreased Cd accumulation in tomato shoots, roots, and fruits by 37%, 40%, and 93%, respectively, accompanied by reductions of 6% and 56% in the translocation factor and biological concentration factor, respectively. Furthermore, electrolyte leakage and the contents of proline, malondialdehyde, and hydrogen peroxide decreased by 77%, 50%, 94%, and 79.9%, respectively, whereas the activities of antioxidant enzymes, including polyphenol oxidase, peroxidase, catalase, and superoxide dismutase, increased by 129%, 80%, 81%, and 59%, respectively. These improvements in soil biochemical properties and plant physiological responses were associated with an 80.8% increase in tomato yield. Overall, the synergistic application of biochar and mycorrhizal fungi effectively alleviated Cd toxicity, improved soil biochemical functioning, enhanced antioxidant defense, and promoted tomato growth and productivity under saline stress.