Effects of biochar and arbuscular mycorrhizal fungi on growth and water status of Chrysanthemum (Chrysanthemum morifolium Ramat.) in outdoor green walls

Abstract With the increasing adoption of green walls as a sustainable approach to improve air quality, mitigate urban heat, and enhance space-use efficiency in cities, the need to produce ornamental plants that are resilient and require fewer chemical inputs has become increasingly important. In this context, the use of biochar and mycorrhizal fungi has emerged as an environmentally friendly strategy. This study was conducted to evaluate the synergistic effects of biochar and mycorrhizal fungi on the growth and physiological traits of chrysanthemum ( Chrysanthemum morifolium Ramat.) using a factorial experiment arranged in a randomized complete block design with three replications during 2024–2025. Treatments consisted of four biochar levels (0, 2, 3, and 5% w/w of the substrate) and four mycorrhizal inoculation treatments (non-inoculated control, Glomus intraradices , G. mosseae , and a combination of the two strains). The results showed that increasing biochar levels and mycorrhizal inoculation significantly improved growth and morphophysiological indices of chrysanthemum. The treatment consisting of 5% biochar combined with G. intraradices produced the highest leaf number (29.43), leaf dry weight (11.07 g), and growth index (145,559.83 cm 3 ), representing increases of 54%, 103%, and 722%, respectively, compared with the control. The greatest plant height (68.1 cm) was observed in the treatment with 5% biochar combined with G. mosseae . The combined application of 5% biochar and the two fungal strains also resulted in a significant increase in leaf fresh weight (75.15 g) and leaf area (1233.18 mm2). In terms of physiological traits, the highest relative water content (83.71%) was recorded in the 3% biochar treatment with G. intraradices , while the lowest electrolyte leakage (64.01%) was observed under 5% biochar combined with G. mosseae . In addition, chlorophyll a and b concentrations reached their maximum values in the 3% and 0% biochar treatments, respectively, when combined with G. intraradices . In contrast, the highest chlorophyll a/b ratio (2.42) and total pigment content (1.3 mg g −1 fresh weight) were recorded in the 5% biochar treatment with the combined fungal inoculum. Overall, the results demonstrated that biochar application—particularly at the 5% level—when combined with G. intraradices or dual mycorrhizal inoculation, markedly enhanced growth, physiological efficiency, and plant water status in chrysanthemum. This approach can therefore be considered an effective strategy for improving plant performance in outdoor green wall systems while reducing reliance on chemical inputs in urban green infrastructure.