Growth of Native Aromatic Xerophytes in an Extensive Mediterranean Green Roof as Affected by Substrate Type and Depth and Irrigation Frequency

Abstract

<jats:p>Green roofs could be a way to increase vegetation in the center of old Mediterranean cities. The need for conservation of local character and biodiversity requires the use of native plant species, whereas the deficiency of water, particularly in semiarid regions, requires the use of species with reduced irrigation needs. Moreover, the aged buildings lead to the use of lightweight green roof constructions. Therefore, research was undertaken to investigate the possibility of using three Mediterranean aromatic xerophytes, <jats:italic>Artemisia absinthium</jats:italic> L., <jats:italic>Helichrysum italicum</jats:italic> Roth., and <jats:italic>H. orientale</jats:italic> L., at an extensive green roof in Athens, Greece. Simultaneously, the possibility of using locally produced grape marc compost was investigated. Substrate type and depth and irrigation frequency effects on growth of these species were studied. Rooted cuttings were planted mid-May in plastic containers with a green roof infrastructure fitted (moisture retention and protection of the insulation mat, drainage layer, and filter sheet) and placed on a fully exposed third floor flat roof at the Agricultural University of Athens. Two types of substrates were used, grape marc compost:soil:perlite (2:3:5, v/v) and peat:soil:perlite (2:3:5, v/v, as a control), as well as two substrate depths, 7.5 (shallow) and 15 cm (deep), and two irrigation frequencies, sparse (5 or 7 days in shallow and deep substrate, respectively) and normal (3 or 5 days in shallow and deep substrate, respectively). Increased contents of macroelements, total phosphorus (P) and potassium (K) in particular, were recorded in the compost-amended substrate, whereas both substrates had similar physical properties. Plant growth was recorded from May to October. The deep compost-amended substrate, independent of irrigation frequency, resulted in taller plants with bigger diameter and aboveground dry weight in all species. However, a remarkable result was that shallow compost-amended substrate with sparse irrigation resulted in similar or even bigger plant growth of all plant species compared with deep peat-amended substrate with normal irrigation. Thus, all three species were found suitable for use in Mediterranean extensive or semi-intensive green roofs, whereas the use of grape marc compost in the substrate allowed for less water consumption and the reduction of substrate depth without restriction of plant growth at the establishment phase and the first period of drought.</jats:p>

Adapting green roof irrigation practices for a sustainable future: A review

“…Ntoulas et al (2012),Papafotiou et al (2013),Razzaghmanesh et al (2014b), and 451Santamouris et al (2007) are in agreement with the deficit irrigation regime, but the regime 452 applied bySchweitzer and Erell (2014) is too high in this respect.453 Coastal Mediterranean areas like for example Oregon (KCC: Csb) have dry summers but are 454 slightly cooler than interior Mediterranean regions. It is possible to install unirrigated green 455 roofs in this climate, especially if only succulent species are applied (Nagase & Dunnett, 456 2010…”

Relationships between plant drought response, traits, and climate of origin for green roof plant selection

“…Climate is the ultimate driver of broad-scale ecosystem composition and structure, and temperature and precipitation have large influences on the distribution of species (Birks et al 2000, Birks andBirks 2014). Although plants for green roofs in hot and dry climates have often been selected from dry environments as part of the habitat template approach (MacIvor et al 2011, Farrell et al 2013, Papafotiou et al 2013, the influence of a species climate of origin on plant performance on green roofs has not been investigated. Species from climates with greater HMI endure drier and hotter conditions, and this may indicate greater potential for tolerance of water-deficit conditions (Aspinwall et al 2013).…”

Effect of substrate depth on initial growth and drought tolerance of Sedum lineare in extensive green roof system

“…The major component of substrates are mineral-based or inorganic materials such as expanded slate, shale, or clay, sand, pumice, perlite, vermiculite, and crushed recycled clay bricks or tiles (Beattie and Berghage, 2004;Dunnett and Kingsbury, 2004). A small amount of organic materials, such as peat and compost, are often used to amend the substrate (Papafotiou et al, 2013).…”