Crithmum maritimum growth in extensive green roof systems with different substrate type, depth and irrigation regime

Plants growing on extensive green roofs of the Mediterranean experience increased stresses mainly due to summer drought and heat. Therefore 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 Crithmum maritimum 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 by substrate Pum₅₀:Per₂₀:C₂₀:Z₁₀. From December 2011 to July 2012 growth was enhanced in the deeper substrates (15 cm) compared to the shallow ones (7.5 cm) and at the high irrigation regime (60% ET_c). LSR was increased in substrate Pum₄₀:CL₄₀:P₈:C₇:Z₅ during the summer of 2012 indicating increased drought stress compared to substrate Pum₅₀:Per₂₀:C₂₀:Z₁₀. LSR was also increased in the deeper substrates (15 cm) in late spring and early summer of 2012. Based on the results C. maritimum constitutes a good candidate for Mediterranean extensive green roofs even with shallow depths and low irrigation regime.