Carbon Isotope Discrimination of Three Kentucky Bluegrass Cultivars with Contrasting Salinity Tolerance

tolerant cultivars showing less growth reduction than sensitive cultivars under saline conditions (Qian et al., We evaluated leaf C isotope discrimination as affected by salinity 2001; Suplick-Ploense et al., 2002). Growth reduction among three Kentucky bluegrass (Poa pratensis L.) cultivars that differ in their salt tolerance. ‘Moonlight’, ‘NorthStar’, and ‘P-105’ under salt stress could be attributed to excessive ion Kentucky bluegrass (KBG) were grown in solution culture and exaccumulation in the plant tissue and/or to water stress posed to salinity levels of 2.0, 5.0, 8.0, 11.0, and 14.0 dS m 1 for 12 due to low external osmotic potential resulting from sawk. All cultivars exhibited increased leaf firing with increasing salinity. linity. However, Moonlight and NorthStar exhibited less leaf firing than Selection for salt tolerant species and/or cultivars in P105 at all salinity levels. The salinity levels that caused 25% shoot the field is time consuming and difficult due to spatial growth reduction were 4.9 dS m 1 for NorthStar and Moonlight and and temporal variations of salinity level and salt compo4.1 dS m 1 for P105, indicating that Moonlight and NorthStar have sition. Measurement of C isotopic composition and better salinity tolerance than P105. When salinity level was in the in nonstressed, controlled environments has been found range of 2.0 to 8.0 dS m 1, Moonlight produced 1.9-fold more root mass than NorthStar, and NorthStar exhibited 3.9-fold more root mass to be related to water use efficiency in the field, producthan P105. When salinity exceeded 8.0 dS m 1, NorthStar had similar tion under water stress conditions, and plant–environroot mass as Moonlight, and both showed greater root mass than mental interactions in many cool-season grasses (FarP105. Cultivar P105 had a higher C isotope discrimination ( ) than quhar and Richards, 1984; Johnson et al., 1990; Johnson Moonlight and NorthStar under nonsaline conditions ( 2 dS m 1) and Bassett, 1991). Ebdon et al. (1998) reported that C but a lower than Moonlight and NorthStar at 11.0 dS m 1 salinity. isotope discrimination is a useful criterion for assessing The great reduction in of P105 as salinity increased suggests that water use efficiency in KBG. It is unknown if is associsalinity induced a greater degree of stomatal resistance that provided ated with KBG salt tolerance and if low of KBG less opportunity for discrimination against the heavier isotope. Carbon grown under nonsaline conditions would provide an isotope discrimination may serve as a useful selection criterion in breeding efforts to develop salt tolerant KBG. indirect indication of salt tolerance. If can be shown to reliably predict salinity tolerance in KBG, it would provide a useful tool for rapid screening of KBG germplasm for salinity tolerance. S problems in turfgrass sites are becoming more Approximately 1.1% of the C in the biosphere is in common for a number of reasons: accelerated urban the form of the stable isotope 13C. The ratio of 13C/12C development in arid and semiarid western regions where in plant dry matter of C3 plants is lower than the ratio salinity problems are common, the use of reclaimed wasteof the source air due to plants’ discriminations against water or other irrigation waters containing salts, sea13C during diffusion of CO2 through stomata and during water intrusion into turf facilities located on coastal the process of CO2 fixation by ribulose-1,5-bisphosphate sites, water conservation, and road deicing (Carrow and carboxylase (rubisco). The degree of discrimination Duncan, 1998). Limited water resources in the western against 13C differs among species and varies with envistates increasingly force turf facilities to use low quality ronments. Higher degree of discrimination results in a water for irrigation. Water conservation efforts can furgreater degree of depletion in 13C in plant tissue in relather increase soil salinity levels due to reduced leaching. Selection and use of relatively salt tolerant cultivars will tion to CO2 in the air. benefit sites where soil and water salinity are marginTwo nomenclatures have been used to describe the ally high. 13C content of plant materials. Isotope composition Although KBG (one of the most widely used cool( 13C) is a value indicating whether the sample has a season turfgrasses in the United States) is generally higher or lower 13C/12C isotope ratio than PDB, a limeconsidered to be salt-sensitive, studies have found that stone standard from Pee Dee, SC (Farquhar et al., 1988). cultivars of KBG differ in their salinity tolerance, with Therefore, isotope composition of a plant tissue ( p) can be expressed as: Y.L. Qian, S. Wilhelm, A.J. Koski, and M.A. Shahba, Dep. of Hortic. p (‰) [(C/C)plant/(C/C)standard] 1 1000 [1] and Landscape Architecture, Colorado State Univ., Fort Collins, CO 80523-1173; and R.F. Follett, USDA-ARS, Soil-Plant-Nutrient Res. Carbon isotope discrimination is a measure of the C Unit, Fort Collins, CO 80522. Received 27 June 2003. *Corresponding author ([email protected]). Abbreviations: Ci/Ca, the ratio of intercellular and atmospheric CO2 Published in Agron. J. 96:571–575 (2004).  American Society of Agronomy concentration; EC, electrical conductivity; KBG, Kentucky bluegrass; , carbon isotopic discrimination. 677 S. Segoe Rd., Madison, WI 53711 USA