Drought stress response of Sedum sediforme grown in extensive green roof systems with different substrate types and depths

- Sedum sediforme growth was investigated on shallow extensive green roof systems.
- S. sediforme can grow sustainably in pumice based substrates even without soil participation.
- S. sediforme can grow sustainably in 7.5 cm substrate depth without any irrigation.
- Chlorophyll and carotenoids concentration are reduced only under severe drought conditions without however affecting plant growth.

Sedums are considered among the best plant species for use on extensive green roof types. The present study evaluated the growth capacity of native Sedum sediforme (Jacq.) Pau in extensive green roof systems that varied in substrate type and depth as well as in the applied irrigation regime. The two substrate types included either soil-less (Pum50:Per20:C20:Z10) or soil-amended substrate (S15:Pum40:Per20:C20:Z5) that comprised sandy loam soil [S], pumice [Pum], perlite [Per], compost [C], and zeolite [Z] at volumetric proportions indicated by their subscripts. Each substrate type was used at two depths (7.5 or 15 cm). During the summer drought periods two different irrigation regimes (high and low) were utilised: (a) in 2010, the high irrigation regime replenished 30% of the cumulated daily pan evaporation (Epan) between consecutive irrigation applications, while the low irrigation regime replenished half of it (15% Epan) and (b) in 2011, the high irrigation regime remained the same as in 2010, while the low irrigation regime was not irrigated at all. Measurements included physical and chemical characterisation of the utilised substrates as well as plant growth and physiological measurements that included plant height, dry weight, chlorophyll and carotenoid determination. It was found that during the first study year plant growth was promoted by the soil-less substrate, which was also depicted in the prolific flowering in the following study year, while chlorophyll and carotenoid content increased in the deeper substrates. By contrast, in the second study year plant growth and physiology was mainly enhanced in deeper substrates, while substrate type was indifferent. Despite the observed differences S. sediforme was able to survive under minimal or no irrigation even at the shallow depth of 7.5 cm and proved to be a native plant species that could successfully be utilised in extensive green roof systems in the Mediterranean and other semi-arid climatic regions.