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Growth of the Mediterranean xerophyte Scabiosa cretica on an extensive green roof under different substrate types and irrigation regimes

Tassoula, L., Papafotiou, M., Galanis, D.
Acta horticulturae 2017 no.1189 pp. 283-286
Mediterranean climate, Scabiosa, grape pomace, green roofs, irrigation scheduling, photosystem II, shoots, soil, stomatal conductance, summer, xerophytes, Greece
The possibility of using Scabiosa cretica L. (Lomelosia cretica (L.) Greuter & Burdet.), an evergreen perennial Cretan subshrub, on extensive green roofs was tested. Rooted stem cuttings were planted in December 2012, in experimental modules with a green roof infrastructure on a fully exposed flat roof at the Agricultural University of Athens, Athens, Greece. The experiment lasted 21 months. Two types of substrate with 10 cm depth were used, one with soil, i.e., grape marc compost:perlite:soil:pumice (3:3:2:2, v/v) and a lighter one without soil, i.e., grape marc compost:perlite:pumice (3:3:4, v/v). Two irrigation frequencies were applied during the two dry periods (summers), normal and sparse, when substrate moisture was 17-20% and 5-9%, respectively, i.e., every 3 days (normal) and 5 days (sparse), with an exception in August 2014, when the normal irrigation was applied every 2 days and the sparse every 4 days. Shoot number at the end of the second dry period (Sept. 2014) was highest in plants grown on soil-substrate and irrigated normally during summers, while the less shoots were produced by plants grown on soil-substrate and irrigated sparsely. Concerning the monthly plant horizontal expansion, at the end of the first dry period (Sept. 2013), normal irrigation resulted in slightly bigger horizontal expansion, but after the second dry period, at the end of the experiment, plants in all treatments had similar horizontal expansion. Stomatal resistance (Rleaf) one day before irrigation was increased in plants under sparse irrigation indicating water limitation, and maximum quantum yield of PSII (ΦPSII) was smaller in those plants, but no evidence of damage to the photosynthetic apparatus was recorded in any of the treatments. In conclusion, Scabiosa cretica grew very satisfactory even under sparse irrigation and light substrate, and proved appropriate for use on extensive green roofs in areas with semi-arid Mediterranean climate.