Effect of substrate type and cultivation position on growth and safety to consume of the edible medicinal species Crithmum maritimum L., in an extensive urban green roof in Athens (Greece)

Considering the beneficial role of green roof technology in urban agriculture, in the present work, the effect of substrate type and cultivation position on growth of Crithmum maritimum L. (Apiaceae) and accumulation of heavy metals in its edible tissues were studied. Plantlets were planted at the end of June 2016 in plastic containers with a green roof infrastructure fitted (comprising moisture retention and protection of the insulation mat, drainage layer and filter sheet) and placed on a fully exposed second floor flat roof at the Agricultural University of Athens, as well as at the level of Iera Odos Street (a moderate traffic street). Two types of substrates 10 cm deep were used: grape marc compost:perlite:pumice (3:3:4, v/v), and grape marc compost:perlite:pumice:soil (3:3:2:2, v/v). Plants were regularly irrigated in the April-October period and their growth was evaluated every month. At the end of June 2017, the upper part of the plants was collected in order to determine its content of heavy metals (Cu, Pb, Ni, Mn and Zn) by atomic absorption spectrometry. Half of the samples of each treatment were washed with running tap water. Eleven months after planting, plants placed at street level were taller and had greater diameter than those placed in the green roof, irrespective of substrate type. Concentrations of heavy metals Pb, Ni and Mn exceeded permissible limits in all treatments, making it unsafe to consume leaves of C. maritimum produced within the urban fabric.