Organic amendment with mushroom residue alleviates salt stress in watermelon seedlings

Salinity is a major abiotic environmental stress factor that constrains agricultural productivity globally. High-salinity environments not only inhibit crop growth but also reduce yield and quality. Approximately 100 million tons of mushroom residue are produced annually in China. This residue is rich in organic matter and essential nutrients. To facilitate its use as a resource, this study investigated the effects of amending soil with mushroom residue on watermelon growth and soil quality under 150 mM NaCl stress. Salt stress significantly inhibited watermelon seedling growth, reduced chlorophyll contents, increased reactive oxygen species accumulation in watermelon leaves. It also increased sodium and decreased potassium concentrations in the shoots. However, amending the soil with mushroom residue reduced the salt injury index by 53.6 % and increased the seedling health index by 93.6 % compared to seedlings subjected to NaCl stress alone. Furthermore, in MR-treated plants under NaCl stress, the content of MDA and O₂·⁻ was reduced by 52.46 % and 14.71 %, respectively, while the activities of SOD and POD were increased by 19.94 % and 6.49 %, respectively. The K⁺/Na⁺ ration in the shoots was improved by 3.28 fold, significantly mitigating the effects of salt stress. Furthermore, mushroom residue also improved soil physical and chemical properties (EC, pH, CEC), and soil nutrient (N, P, and K contents), contributing to better plant growth. These findings highlight the potential of mushroom residue as a sustainable strategy to mitigate salt stress in watermelon.