Morphophysiological response of ornamental cabbage (Brassica oleracea var. acephala) to the combined application of biochar and mycorrhizal fungi in a green wall system

Abstract Background Considering the challenges associated with growth medium limitations, moisture fluctuations, and environmental stresses in green wall systems, identifying biological strategies to maintain the growth and visual quality of ornamental plants is essential. Objective This study aimed to investigate the interactive effects of biochar and arbuscular mycorrhizal fungi (AMF) on the morphological and physiological traits of ornamental kale ( Brassica oleracea var. acephala ) in a green wall system. Methods A factorial experiment was conducted in a randomized complete block design with three replications under open-field conditions. Treatments included four levels of biochar (0, 2, 3, and 5% w/w of the substrate) and four levels of mycorrhizal fungi (control without inoculation, Glomus intraradices , G. mosseae , and a mixture of both strains). Results Both main factors and their interaction had a significant effect on plant growth and physiology. The 5% biochar treatment combined with dual inoculation of both mycorrhizal strains resulted in the highest vegetative growth, with a 62% increase in leaf number and a 112% increase in shoot dry weight compared to the control. From a physiological perspective, moderate to high levels of biochar combined with AMF improved plant water status and cellular health. Specifically, 2% biochar with G. mosseae showed the highest relative leaf water content, while 3% biochar combined with mixed mycorrhiza resulted in the lowest electrolyte leakage, indicating improved membrane stability and reduced oxidative stress. Conclusion The combined application of biochar and mycorrhizal fungi enhanced vegetative growth and improved physiological stress indicators in ornamental kale grown under limited-volume substrates. This biological approach has strong potential for optimizing green wall growing media and improving plant adaptability and resilience.