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Ultraviolet (UV) radiation poses a potential stress for plant growth and development due to its effect on photosynthesis and plant productivity. In the northern hemisphere, peakUV radiation exposure is predicted to occur from2010 to 2020,with reduced color from UV-related injury, a possibility for turfgrasses. The objective of this study was to investigate the effects of ultraviolet-B (UV-B) light on turfgrass growth and morphology in three coolseason grasses. Cultivars Barvado tall fescue [Schedonorus arundinaceus (Schreb.) Dumort., nom. cons.], Penncross and L-93 creeping bentgrass (Agrostis stolonifera L.), and Barlenium perennial ryegrass (Lolium perenneL.), were selected because of limited information on their growth and development in elevatedUV conditions at heights of cut above 10 cm.The impact of UV-B light treatment on color, relative growth rate, and tillering was measured over a 4-week period in repeated experiments. Ultraviolet-B radiation levels were measured at 16 kJ·m·d biologically effective UV-B light in growth chambers programmed for a day/night regime of 14/10 hours. Chamber temperatures were maintained at 20 8C day/ 17 8C night. Ultraviolet-B light significantly inhibited tiller production in the first experiment in all grasses except PR, whereas no grasses were inhibited in the second experiment. Relative growth rates in all grasses were significantly lower in UV-B conditions 3 weeks after treatment initiation. Turfgrasses exposed to this level of UV-B light at typical lawn heights-of-cut had lower color ratings compared with the non-UV-Btreated control at 2 weeks after treatment initiation. The experiments demonstrated that exposure to UV-B resulted in a decline of growth rate and color in cool-season turfgrasses within a timeframe of 2 weeks. Coarse-textured turfgrasses [tall fescue (TF)/perennial ryegrass (PR)] may be more adapted to higher UV-B conditions due to morphological differences compared with the finer textured varieties [creeping bentgrass (CB)]. Light plays a crucial role in turfgrass growth and development and is considered most important in wavelengths of 400–700 nm or photosynthetically active radiation (PAR) (Pons et al., 1993). Light wavelengths and spectral distribution vary with environmental conditions (Bell et al., 2000), and there is interest in how degradation of the ozone layer will influence spectral distribution on the earth’s surface (Manney et al., 2011). The decrease in ozone is predicted to significantly increased exposure to wavelengths in the ultraviolet (UV-A 400–320 nm/UV-B 320–290 nm/UV-C 290–100 nm) range (Kerr and McElroy, 1993). The UV-B wavelengths that contact the earth’s surface are predicted to increase in springtime radiation by 50% to 60% from 2010 to 2020 in the northern hemisphere (Taalas et al., 2000). Ultraviolet-B occurs at the range of 290–320 nm (ISO, 2007) and the energy associated with these wavelengths is considered damaging when compared with PAR (Fiscus and Booker, 1995). The reduction in ozone and resulting increase in UV-B has been linked to increased chlorofluorocarbons in the upper atmosphere (Rowland, 1990). Exposure to UV-B causes several morphological and physiological responses in plants. The leaf area index of some Poaceae can vary in response to different levels of UV-B irradiance with increases from 0% to 80% of ambient UV-B resulting in an 88% decrease in TF leaf area. Increased ambient UV-B from 80% to 90%, however, resulted in a 20% increase in specific leaf area (Deckmyn and Impens, 1999). Leaf area increases of 10% and axillary shoot production of 5% were noted in response to UV-B exposure in wheat (monocot, Triticum aestivum L.), and a bean (dicot, Phaseolus vulgaris L.) (Barnes et al., 1990). Root length of Arabidopsis was inhibited by almost 80% after exposure to 2.1 mmol·m·s UV-B (Kim et al., 2002). Reductions in stem elongation and leaf expansion in young plants of long-spined thorn apple (Datura ferox L.) occur in UV-B light (Ballare et al., 1996). Smaller leaf sizes in white clover (Trifolium repens L.) have been linked to intolerance to UV-B exposure as part of lower constitutive productivity (Hofmann, 2000). In bean plants, low levels of PAR (9.9 mol·m·d) combined with UV-B (0.09 mol·m·d) treatments led to a decrease in leaf area of 47% and a decrease in leaf dry weight of 25% (Cen and Bornman, 1990). Ultraviolet light exposure can reduce photosynthesis by 30% due to direct damage to photosystem II (Brandle et al., 1977). Ultraviolet light has varying effects on quality ratings among turfgrasses. Chewings fescue (Festuca rubra L. ssp. commutata Gaud.) is considered the most UV-B-tolerant turfgrass, andkentuckybluegrassPoapratensisL. is considered the least tolerant (Zhang and Ervin, 2009). Quality ratings were reduced by as much as 74% for kentucky bluegrass maintained at 5 cm after 10 d of exposure to 2.8 mol·m·d UV-B. There was cultivar variation in the tolerance of UV-B in the Zhang and Ervin (2009) trial. Darker green kentucky bluegrass cultivars were reported to be more tolerant of UV-B conditions (Ervin et al., 2004). Turfgrass photoinhibition occurs in kentucky bluegrass exposed to 2.8 mol·m·d UV-B, maintained at 6.3 cm through decreasing photochemical efficiency (Fv/Fm) by 70% (Zhang et al., 2005). Physiological responses also vary within turfgrass plants with changes in pigmentation not uniform. CB (A. stolonifera) ‘L-93’ produces more anthocyanins compared with ‘Penncross’ when exposed to UV-B for 7 d (Nangle et al., 2015). Limited research has been conducted to test the effect of UV-B exposure on turfgrasses at higher heights of cut (10 cm) associated with residential lawns. The estimated area covered by irrigated turfgrass is 163,800 km (Milesi et al., 2005), and therefore, a large land area could be affected. The objective of this study was to test three cool-season turfgrasses for their growth rate, tillering, and color responses to elevated UV-B conditions. It was hypothesized that coarser textured species, such as PR and TF (Turgeon, 2008), would have greater tolerance to UV-B than finer textured species such as CB. Materials and Methods Two separate experiments were initiated in Mar. 2011 and May 2011 at The Ohio State University, Columbus, OH. Turfgrasses were Received for publication 17 Apr. 2015. Accepted for publication 26 Jan. 2016. Salaries and research support provided in part by State and Federal funds appropriated to the Ohio Agricultural Research and Development Center, TheOhioStateUniversity. JournalArticleHCS-16-12. Present address: Chicago District Golf Association, 11855 Archer Avenue, Lemont, IL 60439. Corresponding author. E-mail: Gardner.254@osu.edu. HORTSCIENCE VOL. 51(4) APRIL 2016 439 TURF MANAGEMENT

Cool-season Turfgrass Color and Growth Habit Response to Elevated Levels of Ultraviolet-B Radiation