Optimizing Artificial Soil Mixes for Urban Green Spaces: Plant Growth and Carbon Sequestration Balance

Background and objective: As urbanization accelerates, urban areas are significantly contributing to greenhouse gas emissionsworldwide. Artificial green spaces, such as green roofs, have emerged as vital strategies for mitigating urban carbonemissions while providing essential ecosystem services. However, the existing research in this area predominantly addressesthe carbon sequestration potential of vegetation, leaving the role of soil materials in artificial ground systems underexplored. This study aimed to identify optimal material compositions and blending ratios for Artificial Soil Mixes (ASMs) that enhancecarbon reduction while satisfying essential plant growth requirements. Methods: Eight soil materials frequently used in artificial greening —bottom ash, biochar, zeolite, peat-moss, carbonizedrice hull, humus, vermiculite, and cocopeat—were blended into four distinct ASMs (ASM_A, ASM_B, ASM_C, and ASM_D). Each ASM was assessed based on its (1) physicochemical properties, (2) elemental composition, and (3) plant growthperformance. Results: ASM_A exhibited comparable or slightly superior growth to the control soil, likely due to its high organic mattercontent and cation exchange capacity (CEC). ASM_D demonstrated the highest carbon content (27.60 wt%) among theblends, highlighting its significant potential for long-term carbon sequestration. However, its lower nitrogen and phosphatecontents limited its effectiveness during early plant growth stages. Conclusion: This study contributes by developing lightweight artificial soil mixes that simultaneously support basic plantgrowth and enhance carbon reduction. For improved germination and initial plant growth, ASMs with higher availablephosphorus and organic matter contents are recommended. Conversely, ASM_D, which is rich in recalcitrant carbon,presents greater advantages for long-term carbon mitigation. These findings underscore the necessity of further researchto refine soil blends that optimally balance plant growth and carbon sequestration potential in artificial green spaces suchas rooftop gardens.