Municipal water supply systems are increasingly burdened by population growth, and public utilities often implement water use restrictions during periods of severe drought to ensure an adequate supply of potable water for the population. These water restrictions commonly target discretionary uses such as lawn and landscape irrigation. When considering water restrictions and other water conservation methods, replacing traditional turfgrasses with native or indigenous species is often a favored approach despite the apparent ability of warm-season turfgrasses to withstand and recover from prolonged periods of drought. To enable regulators to make informed decisions, additional information is needed documenting both the maximum duration without added water that allows for turf survival and post-water stress characteristics as affected by water stress duration and genotype.
Although a group of different turfgrasses may experience the same climatic conditions, they may not all experience exactly the same degree of water stress as a result of various modes of drought avoidance. Such mechanisms include deep rooting (Huang et al., 1997a, 1997b; Marcum et al., 1995; Sheffer et al., 1987), rapid water uptake from deeper soil layers (Huang et al., 1997b), root branching at lower depths (Marcum et al., 1995), and preconditioning to water stress (Qian and Fry, 1996, 1997). More recent breeding efforts to develop dwarf-type grasses with lower mowing heights and greater plant densities have tended to result in shorter root systems and increased susceptibility to water stress (Qian et al., 1997; White et al., 1993).
The onset of limited soil moisture triggers a host of physiological actions within turfgrass plants. Increased levels of abscisic acid and reduced levels of cytokinin have been correlated with drought conditions and reduced levels of growth and transpiration (Assmann and Shimazaki, 1999; DaCosta and Huang, 2007). During the initial stages of drought, an increased amount of carbon is partitioned to the root system to increase root growth and exploration of the soil for water followed by increased carbon storage as carbohydrates in the leaves and stems for future use during drought recovery (DaCosta and Huang, 2006). Under severe drought conditions, many root and stem cells suffer damage to cell membranes causing leakage of solutes and electrolytes, which result in increased resistance to water transport and ultimately leads to plant death (Boyer, 1971; Huang et al., 1997b). Field evidence collected by Griffin and Hoffmann (2012) showed that mortality of two alpine grass species (P. hothamensis and P. hiemata) in Australia was directly related to the amount of plant-available water in the upper 6 cm of soil. Thus, drought of sufficient magnitude and duration may result in the death of the entire plant.
Recovery of turf from drought stress has only been studied to a limited extent and largely with cool-season grasses such as tall fescue (Huang et al., 1998), kentucky bluegrass (Wang and Huang, 2004), and bentgrass (DaCosta and Huang, 2007). Heckathorn et al. (1997) found that nitrogen levels in C4 prairie grasses were reduced during drought periods resulting in lower enzyme levels, which lowered photosynthetic activity for at least 14 d after the end of the drought period. Cathey et al. (2011) studied turf response to increasing water stress as measured by reduced transpiration rates in a greenhouse experiment and found that zoysiagrass reflected less stress in the plants as compared with bahiagrass and st. augustinegrass. The lower stress in zoysiagrass was attributed to a combination of this grass having a longer time of acclimation as a result of lower transpiration rates and greater osmotic regulation resulting in higher turgor pressures.
The present study was conducted to evaluate the recuperative potential of transplanted plugs of 24 commonly grown cultivars of three species of warm-season turfgrasses subjected to varying amounts of water stress caused by prolonged withholding of water to plants grown in restricted (10 cm) and unrestricted root zones.
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