Abstract Elucidating the organ-specific physiological and biochemical responses of spinach to amino acid-based biostimulants under salt stress is essential for developing sustainable strategies in salt-affected agricultural systems. However, comprehensive knowledge about how different application modes mediate these responses across root, petiole, and leaf tissues remains limited. We investigated growth parameters, pigment contents, oxidative stress markers, antioxidant enzyme activities, mineral nutrition, ionic ratios, phenolic compounds, flavonoids, and antioxidant capacity of Anlani F1 spinach under foliar and soil-applied aminosol and NaCl stress conditions. Application mode and treatment significantly influenced all measured parameters ( p ≤ 0.05). Soil-applied aminosol consistently demonstrated superior stress mitigation, maintaining higher photosynthetic pigment levels, better growth performance, stronger antioxidant defenses, and more effective osmoregulation through enhanced proline accumulation compared to foliar application. Ionic homeostasis was also more effectively restored by soil-applied aminosol, with greater reductions in Na accumulation and more favorable Na/K and Na/Ca ratios across all tissues. Secondary metabolite responses differed markedly between application modes, with soil-applied aminosol producing higher accumulation of quercetin, catechin, total phenolic and flavonoid contents, and greater DPPH radical scavenging activity, consistent with up-regulation of the phenylpropanoid biosynthetic pathway. Antioxidant enzyme distribution revealed a distinct tissue-specific pattern, with APX, POD, and SOD activities peaking in leaves while CAT activity was predominantly elevated in roots, indicating compartmentalized defense regulation. Multivariate analyses including PCA and hierarchical clustering distinguished NaCl-stressed groups from aminosol-treated clusters, indicating a marked shift in the overall physiological and biochemical profile. We conclude that application mode significantly influences aminosol efficacy in mitigating salt stress, with soil application emerging as the superior strategy for enhancing spinach resilience under saline conditions. Differential organ-specific responses provide insights for optimizing biostimulant application protocols, while the quantitative stress response patterns identified offer valuable parameters for improving spinach productivity in salt-affected cultivation systems.
Turfan et al. (Tue,) studied this question.
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