Water resources continue to be depleted as the world’s population grows. American families can use up to 1500 L of water per day, and more than 50% may be used outdoors (Smith and Brown, 2003). Alig et al. (2004) used population and land development models to predict urbanization to increase by as much as 80% between 2004 and 2025, indicating more land will be used for irrigated residential and commercial landscapes. This, along with already limited water supplies, illustrates a need for conserving water in the lawn and landscape. Selection of drought-tolerant species for use in the landscape may be one solution.
It is not uncommon for water municipalities to impart water restrictions on residential landscapes, which can cause plants to experience drought stress. Including plants in the landscape that have the ability to maintain their quality longer or experience dormancy during drought, and recover afterward, would be beneficial in areas with water restrictions and contribute to reduced water use in areas without water restrictions. A number of studies have evaluated drought tolerance of turfgrass species in the greenhouse or growth chamber (Huang and Gao, 1999; Jiang and Huang, 2001; Liu et al., 2007; Qian and Fry, 1997) or in the field (Hook et al., 1992; Karcher et al., 2008; Merewitz et al., 2010; Richardson et al., 2008; Steinke et al., 2010). Few studies, however, have assessed drought resistance of ornamental landscape species or directly compared drought resistance between turf and non-turf groundcovers (Devitt and Morris, 2008; Domenghini et al., 2013; Staats and Klett, 1995).
Previous research has indicated succulents such as those in the Sedum genus have performed well on green roofs, where moisture is typically a limiting factor (Bousselot et al., 2010, 2011; Kircher, 2004; Monterusso et al., 2005). One reason Sedum is well suited for possible drought situations such as on green roofs is that it has the ability to switch from using a C3 photosynthetic pathway to a crassulacean acid metabolism photosynthetic pathway when growing in an environment where water is limiting (Phillips and Burrell, 1993; Sayed et al., 1994). This minimizes water loss during the day, when temperatures and evaporation are highest.
Among cool-season grasses, Poa pratensis is the most commonly used in the United States for residential and commercial lawns, parks, and golf courses (Christians, 2004; Lyman et al., 2007; Turgeon, 2005). One advantage of P. pratensis is its ability to survive during extended drought through dormancy (Christians, 2004; Goldsby, 2013). Drought resistance of P. pratensis has been studied by initiating severe drydowns and evaluating plant responses (Keeley and Koski, 2001; Liu et al., 2007; Merewitz et al., 2010; Richardson et al., 2008, 2009). Richardson et al. (2009) found wide variation in responses to drought among P. pratensis cultivars and suggested selection of better-performing cultivars could result in water conservation.
Turfgrasses are often singled out for replacement by presumably more water-efficient plant species to save water. For example, in 2006, the U.S. Environmental Protection Agency (EPA) created a voluntary program called WaterSense to promote water efficiency (WaterSense, 2008). This program lists criteria for builders to follow to have a home labeled a WaterSense home. At the inception of WaterSense in 2006, the outdoor water efficiency component of the program required a reduction in the area of turfgrass in the landscape for the home to qualify for the WaterSense label. Research is needed, however, to either validate or refute claims that turfgrass uses more water or is less drought-resistant than herbaceous ornamentals.
The objectives of this study were to: 1) evaluate visual drought stress and water status of one turfgrass and eight herbaceous non-turf ornamental landscape species during a severe drydown; and 2) evaluate percentage of green groundcover of the same species during recovery from the severe drydown.
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