title: Drought versus heat: What's the major constraint on Mediterranean green roof plants?
abstract: Green roofs are gaining momentum in the arid and semi-arid regions due to their multiple benefits as compared with conventional roofs. One of the most critical steps in green roof installation is the selection of drought and heat tolerant species that can thrive under extreme microclimate conditions. We monitored the water status, growth and survival of 11 drought-adapted shrub species grown on shallow green roof modules (10 and 13cm deep substrate) and analyzed traits enabling plants to cope with drought (symplastic and apoplastic resistance) and heat stress (root membrane stability). The physiological traits conferring efficiency/safety to the water transport system under severe drought influenced plant water status and represent good predictors of both plant water use and growth rates over green roofs. Moreover, our data suggest that high substrate temperature represents a stress factor affecting plant survival to a larger extent than drought per se. In fact, the major cause influencing seedling survival on shallow substrates was the species-specific root resistance to heat, a single and easy measurable trait that should be integrated into the methodological framework for screening and selection of suitable shrub species for roof greening in the Mediterranean.
authors.affiliation: Dipartimento di Scienze della Vita, Università di Trieste, Via L. Giorgieri 10, 34127 Trieste, Italy. Electronic address: tsavi@units.it.
authors.forename: Tadeja
authors.initials: T
authors.lastname: Savi
authors.affiliation: Dipartimento di Scienze della Vita, Università di Trieste, Via L. Giorgieri 10, 34127 Trieste, Italy. Electronic address: dalborgo.anna@gmail.com.
authors.forename: Anna
authors.initials: A
authors.lastname: Dal Borgo
authors.affiliation: Dipartimento di Scienze della Vita, Università di Trieste, Via L. Giorgieri 10, 34127 Trieste, Italy; Department of Landscape, University of Sheffield, Western Bank, Sheffield, South Yorkshire S10 2TN, United Kingdom. Electronic address: vllove1@sheffield.ac.uk.
authors.forename: Veronica L
authors.initials: VL
authors.lastname: Love
authors.affiliation: Harpo seic verdepensile, Via Torino 34, 34123 Trieste, Italy. Electronic address: s.andri@seic.it.
authors.forename: Sergio
authors.initials: S
authors.lastname: Andri
authors.affiliation: Dipartimento di Scienze della Vita, Università di Trieste, Via L. Giorgieri 10, 34127 Trieste, Italy. Electronic address: tretiach@units.it.
authors.forename: Mauro
authors.initials: M
authors.lastname: Tretiach
authors.affiliation: Dipartimento di Scienze della Vita, Università di Trieste, Via L. Giorgieri 10, 34127 Trieste, Italy. Electronic address: nardini@units.it.
authors.forename: Andrea
authors.initials: A
authors.lastname: Nardini
keywords: Drought resistance; Heat resistance; Mortality; Shallow substrate depths; Shrub species; Water status