Using the Halophyte Crithmum maritimum in Green Roofs for Sustainable Urban Horticulture: Effect of Substrate and Nutrient Content Analysis including Potentially Toxic Elements

The effect of substrate type and cultivation site in the urban fabric on growth, nutrient content and potentially toxic element (PTE) accumulation in tissues of the halophyte Crithmum maritimum was studied. Plantlets were cultivated for twelve months in containers with a green-roof infrastructure fitted and placed either on an urban second-floor roof or on ground level by the side of a moderate-traffic street. Two substrate types were used; one comprising grape marc compost, perlite and pumice (3:3:4, v / v ) and one composed of grape marc compost, perlite, pumice and soil (3:3:2:2, v / v ), with 10 cm depth. Plants grew well on both sites, although aboveground growth parameters and nutrient content in leaves were greater at street level. Both cultivation site and substrate type affected heavy-metal accumulation in plant tissues. Cu, Ni and Fe concentrations in leaves and Pb in roots were higher in street-level-grown plants compared to the roof-grown plants, and concentrations of Cu and Mn in leaves and Fe in both leaves and roots were lower in the soilless substrate compared to the soil-substrate, making the soilless type preferable in the interest of both safer produce for human consumption and lower construction weight in the case of green-roof cultivation.