Evaluating the establishment performance of six native perennial Mediterranean species for use in extensive green roofs under water-limiting conditions

The rapid growth of many Mediterranean cities in the past 50 years has led to a deficit of urban green space where water availability is the main limiting factor. The aim of this experiment was to evaluate the establishment performance of six Mediterranean species for use in extensive green roofs in Mediterranean and semi-arid areas. Asteriscus maritimus, Brachypodium phoenicoides, Crithmum maritimum, Limonium virgatum, Sedum sediforme and Sporobolus pungens plants were grown under well-watered conditions and two levels of water-deficit conditions to assess the effects of water-deficit on their growth capacity, water consumption, photosynthetic capacity, water relations and aesthetic value (relative appearance). After 88 days, the results showed that the water-deficit treatments affected each species differently and revealed differences in the potential ecosystem service benefits that different species could provide. Sedum sediforme appeared to be the best adapted species to water-deficit in terms of relative appearance; however, this species had the lowest capacity to grow (between 7.55 and 4.72 g) and consume water (between 1.58 and 0.82 mm day(-1)) under both well-watered and water-deficit conditions, limiting its usefulness for storm water management. Brachypodium phoenicoides and Limonium virgatum showed a satisfactory aesthetical performance under water-deficit conditions and had higher water consumption (between 7.66 and 3.48 mm day(-1)) and biomass accumulation (between 40.11 and 18.98 g) than Sedum sediforme. By contrast, Asteriscus maritimus showed variable relative appearance results than that species. Crithmum maritimum, a succulent species, showed similar biomass accumulation and water consumption to S. sediforme but lower relative appearance than that species. Sporobolus pungens, a C-4 species, showed the highest water use efficiency at the plant level (between 5.79 and 4.81 g L-1). In summary, B. phoenicoides and L. virgatum are suggested as interesting species to complement S. sediforme in Mediterranean and semi-arid green roofs.