Chitooligosaccharide enhances saline–alkaline stress tolerance in Brassica rapa

Saline–alkaline soils pose significant challenges to agricultural productivity and crop growth. This study investigates the effects of chitooligosaccharide (COS) administration on the growth, ion homeostasis, and antioxidant defense systems of Brassica rapa in saline–alkaline field conditions over two consecutive growing seasons (2022–2023). The results showed that COS treatments significantly increased both shoot and root biomass, with the 0.3 g L −1 dosage yielding the highest total weight based on statistical analysis ( p < 0.05). COS also enhanced chlorophyll content, reduced Na + /K + ratios, and stimulated antioxidant enzyme activities such as superoxide dismutase and catalase, while decreasing malondialdehyde accumulation. These findings suggest that COS enhances plant resilience to salt–alkaline stress by promoting biomass development, maintaining ionic balance, and strengthening oxidative defense mechanisms. This work demonstrates the potential application of COS as a sustainable biostimulant for agricultural practices in saline–alkaline environments.