Kentucky bluegrass, tall fescue, and japanese zoysiagrass are commonly used for sports and recreational areas. Turfgrasses used for recreational areas are frequently subjected to traffic stress (Bonos et al., 2001; Li and Hunt, 1997; Minner and Valverde, 2005). The term traffic stress generally includes both wear and soil compaction (Beard, 1973; Carrow and Petrovic, 1992). Soil compaction may result in poor soil physical properties, and inhibits turfgrass root growth and visual quality (Trenholm et al., 2000; Turgeon, 2005). Wear causes a direct injury to plant tissues by pressure, scuffing, abrasion, and tearing (Beard, 2005; Bonos et al., 2001; Carrow and Petrovic, 1992). Wear injury results from the weight and motion of traffic crushing and tearing the leaves, stems, and crowns of the turfgrass plant (Carrow and Petrovic, 1992; Shearman and Beard, 1975a, b; Trenholm et al., 2000).
It has been reported that warm-season turfgrass species have more tolerance to wear than cool-season species (Shearman and Beard, 1975a, b). Among warm-season turfgrass species, japanese zoysiagrass and bermudagrass (Cynodon dactylon) are the species with more wear tolerance (Turgeon, 2005). Among cool-season species, tall fescue, kentucky bluegrass, and perennial ryegrass (Lolium perenne) are considered to have relatively more wear tolerance (Minner and Valverde, 2005). However, the underlying physiological mechanisms for the difference in wear tolerance between species are poorly understood. Relative wear tolerance of different species has varied among different studies (Canaway, 1981; Carrow and Petrovic, 1992; Minner and Valverde, 2005; Shearman and Beard, 1975a).
Turf cover, visual quality, and shoot density have been commonly used to evaluate wear tolerance (Canaway, 1981; Shearman and Beard, 1975a). Bourgoin et al. (1985) investigated plant characteristics that correlated to wear tolerance and found that high initial tillers per unit area are related to wear tolerance in tall fescue, kentucky bluegrass, and perennial ryegrass. Within perennial ryegrass cultivars, higher leaf water content (LWC) and higher acid detergent fiber (lignin and cellulose) shoot tissue content tended to be related to wear tolerance. Trenholm et al. (2000) indicated that bermudagrass wear tolerance was most strongly correlated with increased stem moisture content and stem cellulose content.
It has been well documented that antioxidant defense mechanisms are involved in plant tolerance to stresses (Inze and Montagu, 2002). Various abiotic and biotic stresses may reduce photosynthetic rates. Chloroplasts may be exposed to excess excitation energy, especially under high light (Inze and Montagu, 2002). Electrons leaked from electron transport chains in the chloroplasts can react with O2 to produce reactive oxygen species (ROS) such as hydrogen peroxide (H2O2). The excess ROS may cause damage to the cell membrane through lipid peroxidation, proteins, and nucleic acids. Plants have various antioxidant metabolites and enzymes to cope with the ROS. Peroxidase (POD) is an antioxidant enzyme that can scavenge H2O2. Research has shown that H2O2 and POD are involved in cell wall stiffening during plant hypersensitive reactions against pathogen attack (Bestwick et al., 1997; Schopfer, 1996). Stiffened cell walls have less flexibility and may be more susceptible to wear injury. However, few studies have been reported responses of antioxidant enzymes (e.g., POD) to traffic stress. Little information is available regarding physiological responses to traffic stress in cool-season and warm-season turfgrass species. This study was conducted to determine the physiological responses of three turfgrass species to different levels of traffic stress, and to investigate whether antioxidant defense is involved in traffic stress tolerance of turfgrasses.
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