Relationships between plant drought response, traits, and climate of origin for green roof plant selection

Abstract

The ideal species for green or vegetated roofs should have high water use after rainfall to maximize stormwater retention but also survive periods with low water availability in dry substrates. Shrubs have great potential for green roofs because they have higher rates of water use, and many species are also drought tolerant. However, not all shrub species will be suitable and there may be a trade-off between water use and drought tolerance. We conducted a glasshouse experiment to determine the possible trade-offs between shrub water use for stormwater management and their response to drought conditions. We selected 20 shrubs from a wide range of climates of origin, represented by heat moisture index (HMI) and mean annual precipitation (MAP). Under well-watered (WW) and water-deficit (WD) conditions, we assessed morphological responses to water availability; evapotranspiration rate (ET) and midday water potential (Ψ ) were used to evaluate species water use and drought response. In response to WD, all 20 shrubs adjusted their morphology and physiology. However, there were no species that simultaneously achieved high rates of water use (high ET) under WW and high drought tolerance (low Ψ ) under WD conditions. Although some species which had high water use under WW conditions could avoid drought stress (high Ψ ). Water use was strongly related to plant biomass, total leaf area, and leaf traits (specific leaf area [SLA] and leaf area ratio [LAR]). Conversely, drought response (Ψ ) was not related to morphological traits. Species' climate of origin was not related to drought response or water use. Drought-avoiding shrubs (high Ψ ) could optimize rainfall reduction on green roofs. Water use was related to biomass, leaf area, and leaf traits; thus, these traits could be used to assist the selection of shrubs for stormwater mitigation on green roofs. The natural distribution of species was not related to their water use or drought response, which suggests that shrubs from less arid climates may be suitable for use on green roofs. Selecting species based on traits and not climate of origin could both improve green roof performance and biodiversity outcomes by expanding the current plant palette.

Fast plants have water‐use and drought strategies that balance rainfall retention and drought survival on green roofs

“…Further, when water use was adjusted for shoot dry mass, plants with greater SLA also showed greater water use. This is consistent with other studies that showed positive relationships between water use, shoot dry mass, and SLA (Mitchell et al 2008, Markesteijn and Poorter 2009, Farrell et al 2013b, Du et al 2018. For instance, Nagase and Dunnett (2012) showed that for 12 species (forbs, sedums, and grasses) commonly planted on extensive green roofs in England, plants with greater shoot dry mass were more efficient at retaining rainfall, with bigger plants retaining close to 80% of the stimulated high-intensity rainfall.…”

“…2013, Du et al. 2018), plants with high water use are more likely to survive on green roofs through drought‐avoidance strategies.…”

“…Physiological approaches have also been used to select plants for green roofs that have greater water use and drought resistance (Szota et al 2017, Du andArndt 2018). For example, Farrell et al (2013b) showed that non-woody plants originating from rocky outcrops had greater water use when water was abundant but were able to maintain water status (pre-dawn leaf water potential) under water deficit.…”

Functional diversity response to geographic and experimental precipitation gradients varies with plant community type

“…Increased precipitation can increase LNC (Sandel et al, 2010), but most traits and FDis have no significant relationships with increased precipitation in grasslands (Kimball et al, 2016;Xu et al, 2018). For desert shrub or shrub-dominated communities, increased precipitation can increase SLA of shrubs (Xin et al, 2018), but most traits are not related to experimental drought (Carvajal et al, 2017;Du et al, 2018). Furthermore, the available studies have documented inconsistent results on plant community trait responses to precipitation in geographic and experimental variations (Luo et al, 2018;Sandel et al, 2010;Zuo et al, 2017), due to different adaption and response of species to rapid precipitation changes.…”

Water Resilience by Centipedegrass Green Roof: A Case Study

“…The capacity of rainwater retention by the green roof is also dependent on the dynamic changes of water consumption between two rainfall events [18], the period of dry days, and plant drought tolerance [51]. Water loss on green roofs was mainly driven by plant ET [52].…”