Compost enhances growth, phytochemical characteristics, and antioxidant defense in ornamental kale (Brassica oleracea var. acephala) under salinity stress

Salinity is one of the major abiotic stresses limiting plant growth and reducing the sustainability of soilless cultivation systems. This study evaluated the effects of different compost incorporation rates on the morphological, physiological, and biochemical responses of ornamental kale ( Brassica oleracea var. acephala ‘Kamome White’) grown under salinity stress in a peat-based soilless culture. Plants were cultivated with three compost rates (0, 20, and 40%) under four NaCl concentrations (0, 25, 50, and 75 mM). Growth traits, chlorophyll content, root characteristics, phenolic compounds, flavonoids, antioxidant capacity, antioxidant enzyme activities, malondialdehyde (MDA), and hydrogen peroxide (H 2 O 2 ) contents were determined. Increasing salinity generally reduced plant growth and biomass production, whereas compost application alleviated these adverse effects. Among the treatments, the 20% compost incorporation provided the most balanced overall performance by maintaining plant growth, chlorophyll content, and antioxidant capacity under saline conditions. Although the 40% compost treatment promoted root development and enhanced certain antioxidant responses, its higher electrical conductivity limited plant growth under severe salinity. Compost application also increased phenolic compounds, flavonoids, and antioxidant enzyme activities while reducing MDA and H 2 O 2 accumulation, indicating improved oxidative stress tolerance. Overall, incorporating 20% compost into peat-based growing media represents an effective and sustainable strategy for improving ornamental kale performance under saline conditions while reducing peat dependency.