Physiological responses of pakcoy (Brassica rapa ssp. chinensis) to chitosan application under short-term drought stress

Drought stress is a major environmental factor limiting leafy vegetable productivity in greenhouse cultivation. Chitosan is widely reported as a biostimulant that may enhance stress tolerance through physiological and biochemical regulation. This study aimed to evaluate physiological responses of pakcoy (Brassica rapa ssp. chinensis) to foliar-applied chitosan under short-term drought stress conditions. The experiment was conducted in a greenhouse using a factorial design with three chitosan concentrations (0, 1, and 2 g L⁻¹) and three drought durations (0, 2, and 4 days without irrigation prior to harvest). Growth parameters, photosynthetic pigments, proline accumulation, hydrogen peroxide (H₂O₂) content, and leaf area were measured to assess plant responses. Results showed that moderate chitosan application (1 g L⁻¹) helped maintain plant growth and physiological stability under mild drought conditions. In contrast, higher chitosan concentrations increased oxidative responses, indicated by elevated H₂O₂ and proline levels. Principal component analysis revealed distinct physiological response patterns associated with chitosan dosage and drought duration. The study provides insights into the dose-dependent role of chitosan in modulating physiological responses of leafy vegetables under short-term water deficit.