Effect of Watering Regimen on Chlorophyll Fluorescence and Growth of Selected Green Roof Plant Taxa

Abstract

<jats:p>Green roofs, or vegetative or living roofs, are an emerging technology in the United States. Because environmental conditions are often more extreme on rooftops, many xerophytic plants, especially <jats:italic>Sedum</jats:italic>, are ideal for extensive green roofs because they are physiologically and morphologically adapted to withstand drought. A greenhouse experiment was conducted to determine the effect of watering regimens on plant stress as measured by chlorophyll fluorescence (F<jats:sub>v</jats:sub>/F<jats:sub>m</jats:sub>), biomass accumulation, substrate moisture, and evapotransipiration on succulent plants of <jats:italic>Sedum acre</jats:italic> L., <jats:italic>S. reflexum</jats:italic> L., S. <jats:italic>kamtschaticum ellacombianum</jats:italic> Fisch., and non-Crassulacean acid metabolism (CAM) plants of <jats:italic>Schizachyrium scoparium</jats:italic> Nash and <jats:italic>Coreopsis lanceolata</jats:italic> L. Plants were grown at a substrate depth of 7.5 cm. Results indicate even after the 4-month period, <jats:italic>Sedum</jats:italic> spp. survived and maintained active photosynthetic metabolism to a greater extent than <jats:italic>Schizachyrium</jats:italic> and <jats:italic>Coreopsis</jats:italic>. Furthermore, when <jats:italic>Sedum</jats:italic> was watered after 28 days of drought, chlorophyll fluorescence (F<jats:sub>v</jats:sub>/F<jats:sub>m</jats:sub>) values recovered to values characteristic of the 2 days between watering (DBW) treatment. In contrast, the non-CAM plants required watering frequency every other day to survive and maintain active growth and development. Regardless of species, the greatest increase in total biomass accumulation and fastest growth occurred under the 2 DBW regimens.</jats:p>

Effect of green roof media depth on Crassulacean plant succession over seven years

“…When 18 herbaceous perennials and grasses were evaluated in 10 cm of media without irrigation in Michigan, only four species (Allium cernuum, Coreopsis lanceolata, Opuntia humifusa, and Tradescantia ohiensis) still existed after three years (Monterusso, Rowe, & Rugh, 2005;Rowe, Monterusso, & Rugh, 2006). Other studies have shown similar results (Dunnett, Nagase, & Hallam, 2008;Durhman et al, 2006;Thuring, Berghage, & Beattie, 2010). In all of these studies, if irrigation had been available, then a greater number of species would have likely survived.…”

“…Furthermore, many succulents exhibit some form of Crassulacean Acid Metabolism (CAM) (Lee & Kim, 1994;Sayed, 2001), which helps them tolerate drought conditions. In addition, Durhman, Rowe, & Rugh (2006) found that several species of Sedum survived and maintained active photosynthetic metabolism even after four months without water.…”

Green roof vegetation for North American ecoregions: A literature review

“…In general, Sedum were found to be very reliable genus as they were found to have great endurance for drought tolerance. Many species tolerated up to 1 month without precipitation, and a few Sedum species endured as long as 4 months without water in greenhouse experiments in the South Central Great Lakes ecoregion (Durhman et al, 2006;Durhman et al, 2004;VanWoert et al, 2005). Delosperma Boivin et al (2001) was also found to be successful genus with D. cooperi and D. nubigenum proving successful across many ecoregions (Bousselot et al, 2009;Butler and Orians, 2009;Hauth and Liptan, 2003;Schroll et al, 2009;Wanielista and Hardin, 2006).…”

The relationship between percentage of organic matter in substrate and plant growth in extensive green roofs

“…However, the extreme environmental conditions found on rooftops present challenges for sustaining plant material on green roofs (Durhman, Rowe, & Rugh, 2006): limited water availability, wide temperature fluctuations, and high exposure to wind and solar radiation create a highly stressed, and sometimes disturbed environment (Nagase & Dunnett, 2010). Therefore, for extensive green roofs (thin substrate, lower maintenance requirements and reduced need for irrigation), vegetation such as sedums, alpines and organisms, and substances such as humus made by these organisms (Handreck & Black, 2002).…”