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Understanding how mowing height and soil moisture influence drought resistance mechanisms may lead to better management of seashore paspalum. This research was conducted to evaluate the effect of mowing height and soil moisture replacement on drought tolerance strategies in three seashore paspalum cultivars. In a greenhouse, clear polyvinyl chloride (PVC) root tubes were placed in a black PVC sleeve with a bottom cap drilled with holes for drainage. Sod pieces (10 cm in diameter) of seashore paspalum (Paspalum vaginatum Swartz) cultivars Salam, Excalibur, and Adalayd were planted into these tubes after roots were trimmed. In a split-split experimental design, water regimes applied included control [100% of the total evapotranspiration (ET)] as well as 75%, 50%, and 25% of the total ET. Mowing heights were 45.0, 35, and 25 mm. Visual turf quality, maximum root extension (MRE), root length densities (RLD), total nonstructural carbohydrate content (TNC), shoot reducing sugar content (RSC), and proline content were determined. Turf quality decreased linearly with the decrease in irrigation water applied under the three mowing heights with higher slope at 25.0 mm than at either 35.0 or 45.0 mm. ‘Salam’ turf quality declined only to the unacceptable rating of 5.5 and 4.5 when mowed to 35 and 25 mm, respectively, whereas quality was 6.5 at the mowing height of 45 mm under the water regime of 25% of total ET. ‘Excalibur’ did not show acceptable turf quality at the 25% treatment, whereas ‘Adalayd’ did not show such quality at both 50% and 25% water regimes under all mowing heights. Regression analysis indicated a significant negative association between RLD and drought levels at all mowing heights and soil depths. In ‘Salam’, as drought levels increased from control to 25%, average RLD decreased by 76%, 75%, and 76% at 25-, 35-, and 45-mm mowing heights, respectively, at the top 30 cm of soil in the column. The change was 93%, 85%, and 83% at 25-, 35-, and 45-mm mowing heights, respectively, at the deeper soil (90 to 120 cm). In ‘Salam’, on average overall water regimes, MRE at 45 mm was ’10% to 17% greater than that of 35-mm mowing height and 28% to 36% greater than that of 25-mm mowing height. The highest root mass (810 mg) was obtained when ‘Salam’ was mowed to 45 mm and subjected to the drought level of 50% of the total ET. The lowest root mass (320 mg) was obtained when ‘Salam’ was mowed to 25 mm and the water regime was not limiting. In ‘Salam’, as drought increased from control to 25% of the total ET, average TNC decreased by 43.5%, 26.0%, and 29.0% and the average TNC decrease in ‘Excalibur’ shoots was 48.0%, 30.0%, and 32.0%, whereas the decrease in ‘Adalayd’ was 51.3%, 42.3%, and 35.4% at 25-, 35-, and 45-mm mowing heights, respectively. As drought levels increased from control to 25% of the total ET, average RSC increased by 57.3%, 57.1%, and 53.0% in ‘Salam’ and by 59.4%, 57.0%, and 51.5% in ‘Excalibur’ and 61.2%, 58.1%, and 61.0% in ‘Adalayd’ at 25-, 35-, and 45-mm mowing height, respectively. When drought increased to 25%, average proline content in shoots increased by 435%, 432%, and 431% in ‘Salam’; 404%, 376%, and 324% in ‘Excalibur’; and 257%, 278%, and 302% in ‘Adalayd’, at 25-, 35-, and 45-mm mowing heights. The resistance of paspalum cultivars to moderate to high drought stress can be enhanced by increasing the mowing height that may be related to increased carbon fixation, which favors increased root production. Proline accumulation could add to the drought tolerance through osmoregulation or by acting as a carbon and nitrogen sink for stress recovery. 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, Received for publication 27 Aug. 2013. Accepted for publication 9 Dec. 2013. Current address: Department of Horticulture and Landscape Architecture, Colorado State University, Fort Collins, CO 80523-1173. To whom reprint requests should be addressed; e-mail shahbam@lamar.colostate.edu. HORTSCIENCE VOL. 49(2) FEBRUARY 2014 221 TURF MANAGEMENT

Drought Resistance Strategies of Seashore Paspalum Cultivars at Different Mowing Heights