The water resources available for the irrigation of turfgrass have become increasingly restricted in recent years due to periods of insufficient precipitation, increased domestic, agricultural, and industrial consumption, and contamination of potable water supplies. In many areas, the water deficit has resulted in implementation of water conservation strategies and stringent restrictions in water use. Therefore, developing water-saving cultural practices for turfgrass management is important in areas with a limited water supply. In addition, further insights into the mechanisms that impart low water consumption in turfgrasses can serve as selection criteria for water-saving turfgrass species or cultivars.
The maintenance of cellular hydration is critical for plant survival in water-limiting environments, which may be achieved by one or the combination of drought avoidance traits such as increasing water uptake from the soil and reducing transpirational water loss by stomatal closure, and drought tolerance traits such as water retention for cell turgor maintenance through osmotic regulation (Nilsen and Orcutt, 1996). Various cultural practices have been used for water conservation in turfgrass management, including the use of plant growth regulators (PGRs). Trinexapac-ethyl (TE) is one of the most widely used PGRs in the management of cool-season and warm-season turfgrass species (Fagerness et al., 2002; Heckman et al., 2001; Lickfeldt et al., 2001; McCullough et al., 2006). TE is absorbed quickly by foliage and slows cell elongation by inhibiting the conversion of one form of gibberellic acid (GA20) to another (GA1). TE has been used mainly for clipping reduction, seedhead suppression in annual bluegrass (Poa annua L.), and improvement of overall turf quality in various turfgrass species (Fagerness et al., 2002; Lickfeldt et al., 2001; McCullough et al., 2006). Several recent studies reported that TE also improved turfgrass tolerance to environmental stresses, such as salinity in bermudagrass [Cynodon dactylon (L.) Pers.] (Baldwin et al., 2006), heat stress in kentucky bluegrass (Poa pratensis L.) (Heckman et al., 2001), drought in zoysiagrass (Zoysia japonica Steud.) and perennial ryegrass (Lolium perenne L.) (Jiang and Fry, 1998), and simultaneous drought and heat stresses in creeping bentgrass (McCann and Huang, 2007). Ervin and Koski (2001) reported that TE resulted in lower evapotranspiration (ET) rates and reduced clipping yield in kentucky bluegrass. Previous studies on the influence of TE on turfgrass stress responses mainly focused on growth effects and the reduction in water demand associated with growth inhibition. However, TE may regulate other physiological processes involved in stress tolerance. In an earlier review article, Munns (1988) pointed out that growth reduction under drought stress may also contribute to osmotic adjustment, with a 30% reduction in a relative growth rate of leaves resulting in a reduction in ψS by 0.1 to 0.2 MPa, assuming that assimilation rate of solutes are unaffected. Based on this notion, it is anticipated that TE may also influence drought resistance ability through changing ψS when shoot growth rate is inhibited.
Osmotic adjustment associated with the accumulation of solutes is a major factor regulating dehydration tolerance in higher plants, which is associated with increased movement of water into or reduced water efflux from cells (Blum, 1988). Therefore, osmotic adjustment helps to maintain cell turgor at a given leaf water potential and thus delays wilting of leaves and enables tissues to sustain growth and metabolic and physiological functions at lower plant water status (Munns, 1988). The types of osmotically active solutes associated with osmotic adjustment are diverse and typically include low molecular weight compounds such as amino acids (e.g., proline), ammonium compounds (e.g., glycine betaine), sugars (e.g., fructans, sucrose), polyols (e.g., mannitol), inorganic ions (e.g., potassium, calcium), organic acids (e.g., malate), and hydrophilic proteins [e.g., late embryogenesis abundant (LEA)] (Chaves et al., 2003). How TE may affect the drought tolerance trait of water retention related to osmotic regulation is not well understood. Understanding how improved drought tolerance with TE is related to its effects on different water use characteristics (water loss and/or retention) would provide further insight into drought resistance mechanisms that may be manipulated through plant growth regulation.
The objectives of this study were to examine the effects of TE application on turf growth and water use characteristics for creeping bentgrass subjected to drought stress and to determine changes in the accumulation of solutes involved in osmotic adjustment associated with TE application.
Baldwin, C., Liu, H., McCarty, L.B., Bauerle, W.L. & Toler, J.E. 2006 Effects of trinexapac-ethyl on the salinity tolerance of two ultradwarf bermudagrass cultivars HortScience 41 808 814
Barrs, H.D. & Weatherley, P.E. 1962 A re-examination of the relative turgidity techniques for estimating water deficits in leaves Aust. J. Biol. Sci. 15 413 428
Bates, L.S., Waldren, R.P. & Teare, I.D. 1973 Rapid determination of free proline for water-stress studies Plant Soil 39 205 207
Buysse, J. & Merckx, R. 1993 An improved colorimetric method to quantify sugar content of plant tissue J. Expt. Bot. 44 1627 1629
Chaves, M.M., Maroco, J.P. & Pereira, J.S. 2003 Understanding plant responses to drought-from genes to the whole plant Funct. Plant Biol. 30 239 264
Ervin, E.H. & Koski, A.J. 2001 Trinexapac-ethyl increases kentucky bluegrass leaf cell density and chlorophyll concentration HortScience 36 787 789
Fagerness, M.J. & Yelverton, F.H. 2001 Plant growth regulator and mowing height effects on seasonal root growth of Penncross creeping bentgrass Crop Sci. 41 1901 1905
Fagerness, M.J., Yelverton, F.H., Livingston, D.P. & Rufty, T.W. 2002 Temperature and trinexapac-ethyl effects on bermudagrass growth, dormancy, and freezing tolerance Crop Sci. 42 853 858
Han, S.W., Fermanian, T.W., Juvik, J.A. & Spomer, L.A. 1998 Growth retardant effects on visual quality and nonstructural carbohydrates of creeping bentgrass HortScience 33 1197 1199
Heckman, N.L., Horst, G.L., Gaussoin, R.E. & Young, L.J. 2001 Heat tolerance of kentucky bluegrass as affected by trinexapac-ethyl HortScience 36 365 367
Jiang, Y. & Huang, B. 2001 Osmotic adjustment associated with drought-preconditioning enhanced heat tolerance in kentucky bluegrass Crop Sci. 41 1168 1173
Lickfeldt, D.W., Gardner, D.S., Branham, B.E. & Voigt, T.B. 2001 Implications of repeated trinexapac-ethyl applications on kentucky bluegrass Agron. J. 93 1164 1168
Marcum, K.B. & Jiang, H. 1997 Effects of plant growth regulators on tall fescue rooting and water use J. Turfgrass Mgt. 2 13 27
McCann, S.E. & Huang, B. 2007 Effects of trinexapac-ethyl foliar application on creeping bentgrass responses to combined drought and heat stress Crop Sci. 47 2121 2128
McCullough, P., Liu, H., McCarty, L., Whitwell, T. & Toler, J.E. 2006 Bermudagrass putting green growth, color and nutrient partitioning influenced by nitrogen and trinexapac-ethyl Crop Sci. 46 1515 1525
Rachmilevitch, S., DaCosta, M. & Huang, B. 2006 Physiological and biochemical indicators for stress tolerance 321 356 Huang B. Plant-environment interactions 3rd ed CRC Press Boca Raton, FL
Stier, J.C. & Rogers, J.N. 2001 Trinexapac-ethyl and iron effects on supina and kentucky bluegrasses under low irradiance Crop Sci. 41 457 465
Topp, G.C., Davis, J.L. & Annan, A.P. 1980 Electromagnetic determination of soil water content: Measurement in coaxial transmission lines Water Resource Res. 16 574 582
Young, M.H., Wierenga, P.J. & Mancino, C.F. 1997 Monitoring near-surface soil water storage in turfgrass using time domain reflectometry and weighing lysimetry Soil Sci. Soc. Amer. J. 61 1138 1146
Zhang, X. & Schmidt, R.E. 2000 Application of trinexapac-ethyl and propiconazole enhances superoxide dismutase and photochemical activity in creeping bentgrass J. Amer. Soc. Hort. Sci. 125 47 51