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University of Melbourne (2019)

Using plant water use and drought response strategies and climate of origin to select shrubs for green roofs in dry and hot climates

Du, Pengzhen

Titre : Using plant water use and drought response strategies and climate of origin to select shrubs for green roofs in dry and hot climates

Auteur : Du, Pengzhen

Université de soutenance : University of Melbourne

Grade : Doctor of Philosophy (PhD) 2019

Résumé partiel
Green roofs are a novel urban ecosystem in cities which have potential to mitigate stormwater runoff, cool buildings and provide habitat for biodiversity. Plants on green roofs play an important role in providing these benefits, and therefore appropriate plant selection is critical to ensure survival and maintenance of plant cover. For stormwater retention, plants should have high water use after rainfall events to dry out substrates and maximise water retention for the next rainfall event. However, between rainfall events, green roofs are difficult environments for plants to grow due to shallow substrate depths and low water retention in the free-draining substrate. These stressful conditions are exacerbated in hot and dry climates with prolonged summer water-deficits. Therefore, it is critical to select species with both high water use when water is available and high drought resistance to balance the aims of stormwater retention and survival. Succulents have been widely used on green roofs due to their high survival, but compared with other life-forms, their ability to improve stormwater retention and evaporative cooling are limited due to their low water use. Some monocots and herbaceous species showed the combination of high water use and high drought resistance. Woody species like shrubs also have great potential to be used on green roofs as they can use more water than succulents, and many are highly drought tolerant in their natural habitats. However, shrubs are not yet widely used on green roofs and there is a need to understand what types of shrub species are better suited to green roof conditions. Climate of origin may be a useful way to select drought tolerant shrubs as rainfall distribution and aridity often relates well to plant drought response in natural habitats. Further, physiological traits including the water potential at turgor loss point (tlp), minimum water potentials (min) and the degree of iso-anisohydry are also closely related to water availability in natural ecosystems and could improve green roof plant selection. Therefore, I evaluated whether plant water use and drought response strategies and climate of origin can be used to select shrubs for green roofs in dry and hot climates.
I conducted a glasshouse experiment with well-watered and water-deficit treatments to evaluate the water use and drought response strategies (degree of iso-anisohydry, min and tlp) of 20 shrubs selected across an aridity gradient (quantified by heat moisture index, HMI, calculated as (MAT+10)/ (MAP/1000)) (Chapters 2 and 3). I hypothesized that : 1) there would be higher water users with higher drought resistance ; 2) species from more xeric habitats would have lower water use and higher drought tolerance (Chapter 2) ; and 3) shrubs with lower with lower tlp would be more drought tolerant, more anisohydric and use less water under water-deficit (Chapter 3). I then conducted a green roof module study planted with 15 species from the glasshouse study (130 mm deep substrate) to evaluate their performance under green roof conditions for one year (Chapter 4). I assessed plant recovery after the summer by re-watering in autumn. This chapter aimed to determine whether plant water use and drought response strategies and climate of origin related with plant survival on green roof

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Page publiée le 24 septembre 2019