Substrate type, depth and irrigation regime effects on Ebenus cretica growth in extensive green roof

In an effort to increase the flora palette of Mediterranean extensive green roof systems, it is necessary to evaluate native plants for their capacity to survive and grow on semi-arid roof tops. The current study evaluates growth and physiological indices of the native species Ebenus cretica when growing on two different substrate types [Pum₅₀:Per₂₀:C₂₀:Z₁₀ and Pum₄₀:CL₄₀:P₈:C₇:Z₅ (where Pum: pumice, Per: perlite, C: compost, P: peat, Z: zeolite and CL: clay in volumetric proportions as indicated by the subscripts)], two substrate depths (7.5 and 15 cm) and two irrigation regimes (irrigation applied every 3 days at either 60 or 30% of cumulative daily crop evapotranspiration NDASH ET_c). Measurements included growth index and leaf stomatal resistance (LSR). The study lasted from July 2011 until August 2012. It was found that growth was favored only initially by substrate Pum₅₀:Per₂₀:C₂₀:Z₁₀. The growth was enhanced in the deeper substrates (15 cm) compared with the shallow ones (7.5 cm) while irrigation regime was indifferent. LSR was increased in the 30% irrigation regime and to a lower extend in deeper substrate depth (15 cm) and in substrate Pum₄₀:CL₄₀:P₈:C₇:Z₅. Based on the results E. cretica constitutes a good candidate for Mediterranean extensive green roofs since it managed to survive and grow even at the shallow substrate depth and under the low irrigation regime.