Research PaperThe effect of substrate on growth and nutritional status of native xerothermic species grown in extensive green roof technology

- The modification of the composition of commonly used roof substrate can significantly affect the growth and element concentration in plants.
- Si-waste and other recycled ingredients created a favourable root environment for the examined species, compared to the commercial substrate.
- S.acre L., D. carthusianorum and H. pilosella L. can be suitable for a sustainable green roof design.

The increasing popularity of green roof technology can contribute to urban sustainability and well-being in cities. However, there still is limited knowledge about the effect of substrate, especially composed from waste amendments, on plant species suitable for the extensive green roofs. Currently the urban agglomeration is characterized by a high degree of industrialization and modern agriculture, which contributes to the production of excessive amounts of various waste materials. The usage of locally available waste materials has many potential benefits, including reduced transportation costs, reduced waste disposal and preservation of natural aggregates. However, the waste has to meet many criteria, such as appropriate physical and chemical properties. The main purposes of green roofs in Poland are: to create additional green space in dense urban area and to increase biodiversity, which could be done by using native plants (well adapted to local weather conditions). A 3-year study was carried out in Krakow using a pilot-scale roof system in field containers. Treatments included two substrates-a Si-waste substrate composed of locally available waste materials and a commercial substrate (control)-and three native xerothermic plant taxa: Dianthus carthusianorum, Hieracium pilosella L. and Sedum acre L. The physicochemical properties of substrates, their stability over time and influence on plant nutrient status as well as the visual rating of plants measurements were examined. We observed a tendency to decrease the bulk density and pH value, and a significant increase in the organic matter content in both tested substrates during a subsequent year of the study. The plant nutrient status was similar in terms of macro-elements, regardless of the substrate used. In relation to elevated trace element concentrations in the Si-waste substrate, the amount of metals accumulated in the tissues of all tested taxa was relatively low. We concluded that waste substrate may be a valuable root environment for examined native species which can be successfully used in Europe on green roof plant communities.