The demand for water has increased more than 300% during the past five decades (Huffman, 2004). Therefore, the development of efficient irrigation management programs as well as the improvement of drought resistance of turfgrasses has become extremely important to maintain quality turfgrass.
To reduce water use on turf, it is important to understand the mechanisms of plant adaptation to drought stress in various turfgrass species. Drought resistance includes a range of mechanisms used by plants to withstand periods of drought (Beard, 1989). Strategic mechanisms include drought escape, drought avoidance, and drought tolerance (Turner, 1986). The significance of each of these strategies is related to drought duration and severity in addition to the grass species. These mechanisms are associated with anatomical, morphological, physiological, and biochemical changes. Turfgrasses often concentrate their roots in the upper 30 cm (Beard, 1982). Turfgrasses may resist drought through developing deeper root systems and possessing shoot morphological or physiological mechanisms that reduce ET losses (Beard, 1989). Usually turf quality and ET rate have been used to evaluate drought resistance in turfgrasses (Ebdon and Petrovic, 1997). Root viability and deep rooting have received less attention as criteria to evaluate drought resistance although they have great importance (Huang et al., 1997; White et al., 1992). Deeper and greater root mass and a wider distribution of roots facilitate greater water extraction from the soil (Qian et al., 1997). Changes in leaves that facilitate drought resistance include reduced leaf growth and area, increased pubescence, rolling or folding, and fewer stomates (Duncan and Carrow, 1999).
It has been reported that paspalum has a low water requirement, a moderate fertility requirement, and resistance to mowing at a range of heights in addition to its superior salinity and drought resistance (Marcum and Murdoch, 1990; Shahba, 2010a). These characteristics make seashore paspalum a good alternative warm-season turfgrass such as Cynodon dactylon Pers. (bermudagrass), Zoysia japonica Steud. (zoysiagrass), and Stenotaphrum secundatum Walt. (st. augustinegrass) for arid and semiarid environments. Zinn (2004) reported that under efficient management, paspalum would use 50% less water than bermudagrass. In contrast, Bañuelos et al. (2011) found that bermudagrasses performed better than seashore paspalums at the lowest irrigation levels through enhanced turf recovery, higher quality ratings, higher dry matter production, and lower canopy-air temperature differentials when comparing ‘Tifsport’, ‘Tifway 419’, ‘Tifgreen 328’, and ‘MidIron’ bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Davy] and ‘SeaSpray’, ‘SeaDwarf ’, and ‘Sea Isle 1’ seashore paspalum (Paspalum vaginatum Swartz) under different irrigation levels in Arizona.
Turfgrass species, and cultivars within a species, vary in their stress resistance. These variations often are the result of genetic variations, especially in genes relating to drought resistance mechanisms and their interaction with environments (Duncan and Carrow, 1999). Seashore paspalum has considerable interspecific diversity for various environmental stresses such as salinity, drought, wear, pests, and soil acidity (Duncan, 1999; Lee et al., 2004c; Trenholm et al., 1999).
The balance between carbohydrate production and consumption will impact the ability of turfgrass species to cope with stresses (Huang and Fry, 1999; Lee et al., 2008a, 2008b; Shahba, 2010b). Amino acids, especially proline, accumulate in larger amounts to cope with increasing stress in plants (Lee et al., 2008b). Proline accumulation is one of the first responses of plants exposed to water deficit stress and serves to reduce injury to cells (Ashraf and Foolad, 2007). Rapid accumulation of proline in tissues of many plant species in response to drought, salt, or temperature stresses has been attributed to enzyme stabilization and/or osmoregulation (Flowers et al., 1977; Levitt, 1980). However, because of contrasting reports related to proline accumulation effect on stress tolerance (Marcum, 2002; Torello and Rice, 1986), its use as a selection criterion for stress tolerance has been questioned (Ashraf and Harris, 2004). Thus, it is critical that tests be made before making any conclusion regarding the role of proline in stress tolerance of any specific species.
Turfgrass managers have suggested a mowing height range of 25 to 50 mm for seashore paspalum cultivars. However, mowing at 25 mm or less is a better option because the reduction in mowing height increases turf density and produces plants with shorter internodes. Mowing heights above 50 mm reduce turfgrass density and increase thatch (Brosnan and Deputy, 2009; Lee et al., 2002, 2004b).
Shahba (2010a) and Shahba et al. (2012) concluded that salinity resistance of paspalum cultivars can be enhanced by increasing mowing height. Currently there is no published information that addresses the influence of mowing height and frequency on seashore paspalum drought resistance and rooting characteristics. Knowledge of these effects should help to identify physiological factors involved in drought and close mowing tolerance, which in turn should lead to better management of seashore paspalum turf sites. The objectives of this study were to 1) examine the drought resistance of seashore paspalum cultivars at three mowing heights; 2) to investigate differences in root characteristics and activity in response to soil moisture extraction patterns and ET rate; 3) examine the mechanisms associated with drought resistance such as proline content, TNC, RSC, ET rates, and rooting characteristics.
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