The effects of drought and water conservation efforts on turfgrass quality have been well documented for arid and semiarid regions (Culpepper et al., 2020; Garrot and Mancino, 1994; Kneebone and Pepper, 1982; Meyer and Gibeault, 1986; Serena at al., 2020; Zhang et al., 2019). However, anthropogenic climate change from large migratory influxes into urban areas has triggered an increase in severe, acute drought events throughout the southeastern United States (Seager et al., 2009). Several new policies have been ratified in recent years to regulate potable water and restrict water use for supplemental irrigation (Dai, 2011; Manuel, 2008; Seager et al., 2009). Unfortunately, legislation concerning water use is often drafted and implemented with little regard for short- or long-term effects on managed turfgrass environments. Reductions in turfgrass quality and plant health in response to water restrictions not only affect turfgrass playability but may significantly reduce recreational revenue and property values. Investigation into methods for reducing turfgrass water consumption while maintaining quality may provide a partial solution to this specific problem.
Hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy] and manilagrass [Zoysia matrella (L.) Merr.] are two of the primary warm-season turfgrass species used for home lawns, athletic fields, and golf courses in the southeastern United States (Christians et al., 2016; Turgeon, 2011). Previous research examining the response of turfgrass species to soil moisture has predominantly focused on field and container studies that are limited in their design and implementation (Aronson et al., 1987; Carrow, 1996; Hook and Hanna, 1994; Huang and Gao, 2000; Huang et al., 1997a; Marcum et al., 1995; Qian and Fry, 1997; Qian et al., 1997; Zhou et al., 2012). These studies clearly demonstrated variability in drought response based on turfgrass selection and cultural management practices. However, specific findings are inconsistent and fairly contradictory, further supporting the need for additional research and alternative experimental designs.
Water stress symptomology typically manifests as reduced shoot growth, desiccation and wilting of leaf tissue, and an overall loss of turfgrass quality as a result of compromised cellular growth, root stress, and increased root mortality (Fry and Huang, 2004). Turfgrasses often employ drought avoidance mechanisms including investment in below-ground tissue to maximize water uptake and above-ground tissue to maximize transpiration (Carrow, 1996; Hays et al., 1991; Huang et al., 1997b; Qian et al., 1997). Bermudagrass (Cynodon spp.) generally tolerates higher temperatures and limited water resources better than other turfgrass species (McCarty et al., 2011; Wherley et al., 2014). This may be attributed to the production of a deeper, more extensive root system and aggressive, hardy rhizomes (Duble, 2001). Although zoysiagrass (Zoysia spp.) often produces a shallower root system, intraspecific variability in rooting response has been reported (Zhang et al., 2013). Additionally, Qian and Fry (1997) speculate that leaf rolling along with reduced leaf extension in zoysiagrass may act as an additional drought avoidance mechanism by increasing leaf and canopy boundary layer resistance to evapotranspiration (ET).
Mowing is one of the most basic cultural practices performed on turfgrass environments and can have a major effect on water use efficiency (Harivandi and Gibeault, 1990; Shahba et al., 2014; Wherley et al., 2014). The periodic removal of a portion of shoot growth increases stress on turfgrass plants. This stress significantly affects the ability of turfgrass to withstand abiotic and biotic pressure by inhibiting photosynthetic activity, limiting carbohydrate production and storage, reducing water uptake, and compromising lateral growth (Fry and Huang, 2004). Removal of the cuticle during mowing can also introduce pathogenic stress and lead to increased evaporative losses (Turgeon, 2011). Higher mowing heights typically support deeper, more vigorous roots that have access to larger water reservoirs within the soil profile (Christians et al., 2016). However, increased vegetative material has been found to increase ET rates and ultimately increase plant water requirements (Biran et al., 1981; Feldhake et al., 1983, 1984). Minimal research has examined the interaction of soil moisture and mowing height on bermudagrass and zoysiagrass growth and turfgrass quality. Wherley et al. (2014) investigated the response of zoysiagrass to mowing height and soil moisture using a linear gradient irrigation system (LGIS) but only observed variability among cultivars. Culpepper et al. (2020) compared natural rainfall vs. supplemental irrigation and observed differential responses with respect to turfgrass species but not mowing height.
A variety of experimental approaches has been employed to evaluate the response of plants to soil moisture. Each of these systems presents unique challenges to providing a comprehensive view of plant–water relations. Container studies that used drip irrigation and partial wetting of the upper soil profile to examine cotton (Gossypium hirsutum L.) growth revealed significant disruptions in natural root distribution and restrictions in rooting volume within the plastic cylinders (Plaut et al., 1996). Krizek et al. (1985) suggested that root restriction commonly observed in pot studies can mimic the effect of soil moisture stress even when sufficient moisture is present for normal plant growth. Furthermore, Carrow (1996) established intraspecific and interspecific variability in root response to drought at depths between 20 and 60 cm, asserting that evaluation of deep rooting is critical in determining total drought response. Containers that significantly limit root depth under water deficit may not provide a complete illustration of plant response to soil moisture, particularly for deep-rooting species such as bermudagrass. In recent years, several studies have used LGIS in the field to evaluate turfgrass response to soil moisture (Qian and Engelke, 1999; Wherley et al., 2014; Zhang et al., 2013, 2015). Although LGIS create a continuous and complete moisture gradient, this approach is often subject to environmental variables including precipitation, wind disruption, and malfunctioning irrigation heads. Mueller-Dombois and Sims (1966) developed an alternative method that avoids several of these shortcomings. This approach uses water-table depth gradient tanks that promote natural capillary rise of soil water and offer the opportunity for surface irrigation to simulate rainfall. However, a large amount of greenhouse space, labor, and materials are required to build and house these tanks on site. Furthermore, growing turfgrass on slopes limits establishment to sod, sprigs, or plugs. A standpipe in the front of the tank regulates the water-table depth, whereas capillary rise keeps the low end of the tank at field capacity. Plants are subjected to progressively lower soil moisture levels and greater depth to the water-table when grown at higher elevations of the tank. This methodology allows investigators to measure reduction in turfgrass quality/growth characteristics in response to irrigation restrictions and mowing height on native soil within a controlled environment. Therefore, the objective of our research was to evaluate the response of hybrid bermudagrass and manilagrass to a soil moisture gradient and mowing height using water-table depth gradient tanks.
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