Contents lists available at ScienceDirect Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng Deinking sludge in the substrate reduces the fertility and enhances the plant species richness of extensive green roofs Francesca Vannucchi a , Roberto Pini a , Manuele Scatena a , Giovanni Benelli b , Angelo Canale b , Francesca Bretzel a, ⁎ a CNR-Institute for Ecosystems Studies, Via Moruzzi, 1, 56124 Pisa, Italy b Department of Agriculture, Food and Environment, University of Pisa, via del Borghetto 80, 56124 Pisa, Italy ARTICLE INFO Keywords: Resource availability Nitrogen Life forms Functional groups Flower-visiting insects Recycling ABSTRACT Green roofs provide ecological benefits to urban areas and the use of biodiverse communities enables the ve- getation to recover from stress caused by dry conditions. Recycled waste materials are often used as substrates and extensive research on their physical and chemical properties has been carried out. In this study, we eval- uated different amounts of deinking sludge pellets as an alternative substrate component in establishing drought- tolerant herbaceous communities on green roofs. Three substrates were prepared aimed at providing decreasing fertility: a commercial substrate composed of tephra and compost (control); an experimental substrate composed of tephra, pellets, and compost, and another one consisting of tephra and pellets. A mixture of 30 species, including native herbaceous species and sedum, of Mediterranean phytocenosis, was transplanted on all the substrates. A physical and chemical characterization of the substrates was carried out. The plant ecological functionality, life forms and richness, and the abundance of flower-visiting insects were studied. The substrate composition affected the plant community cover and richness. The amount of pellets in the two experimental substrates reduced the availability of resources (nitrogen and moisture content) promoting diversity, in terms of the number of species, as well as the hardiness of the vegetation. Our results are of great interest for obtaining a biodiverse mosaic habitat in green infrastructures, by measuring out the quantity of infertile materials in the substrates. 1. Introduction Green roofs are ecologically beneficial to the urban environment as they enhance plant and animal diversity. Rooftops are extreme en- vironments in terms of temperature, moisture, light intensity and wind speed, and thus the selection of growing substrates and suitable vege- tation are key to their functionality as well as reducing the management costs (Oberndorfer et al., 2007; Ampin et al., 2010). Roof growing substrates should be stable, permanent and lightweight, and provide nutrients and physical support for the plants (FLL, 2008; www.livin- groof.org). Today many companies produce substrates and technologies aimed at developing these green infrastructures. However, the substrates developed for the continental and northern regions of Europe do not perform well in the south, because of the different climatic conditions, with long droughts in summer followed by heavy rains (Burés, 2013). This has opened a wide door for the studies of roof growing media in the Mediterranean, where the beneficial effects of green infrastructures are urgently needed due to the in- creasing summer heat. While for intensive green roofs, substrate ferti- lity is necessary, as the kind of vegetation and the level of maintenance are similar to real gardens, for extensive green roofs, the right balance of inert and active materials is essential (FLL, 2008). A higher resource availability in the substrates can easily shift the vegetation to a mass of weeds, despite the shallow layer (Cook-Patton and Bauerle, 2012). On the other hand, in a nutrient-deficient habitat, plant development is limited, which facilitates the coexistence of different species, creates gaps for regeneration, limits the biomass of weeds, and requires no maintenance. However not all species are able to adapt to such an environment, especially ruderals which are nitrogen demanding (Grime, 2001). Many studies (Molineux et al., 2009; Ondoño et al., 2015; Ntoulas et al., 2015; Noya et al., 2017) have focused on turning waste into a useful material for growing plants on roofs, such as brick rubble, rice husks, poultry manure, sawdust, compost, paper sludge, however the https://doi.org/10.1016/j.ecoleng.2018.02.027 Received 29 June 2017; Received in revised form 23 February 2018; Accepted 25 February 2018 ⁎ Corresponding author. E-mail addresses: francesca.vn85@gmail.com (F. Vannucchi), roberto.pini@ise.cnr.it (R. Pini), manuele.scatena@ise.cnr.it (M. Scatena), giovanni.benelli@unipi.it (G. Benelli), angelo.canale@unipi.it (A. Canale), francesca.bretzel@ise.cnr.it (F. Bretzel). Ecological Engineering 116 (2018) 87–96 0925-8574/ © 2018 Elsevier B.V. All rights reserved. T