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

Abstract

We evaluated leaf C isotope discrimination as affected by salinity among three Kentucky bluegrass (Poa pratensis L.) cultivars that differ in their salt tolerance. ‘Moonlight’, ‘NorthStar’, and ‘P-105’ Kentucky bluegrass (KBG) were grown in solution culture and exposed to salinity levels of 2.0, 5.0, 8.0, 11.0, and 14.0 dS m−1 for 12 wk. All cultivars exhibited increased leaf firing with increasing salinity. However, Moonlight and NorthStar exhibited less leaf firing than P105 at all salinity levels. The salinity levels that caused 25% shoot growth reduction were 4.9 dS m−1 for NorthStar and Moonlight and 4.1 dS m−1 for P105, indicating that Moonlight and NorthStar have better salinity tolerance than P105. When salinity level was in the 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 than P105. When salinity exceeded 8.0 dS m−1, NorthStar had similar root mass as Moonlight, and both showed greater root mass than P105. Cultivar P105 had a higher C isotope discrimination (Δ) than Moonlight and NorthStar under nonsaline conditions (<2 dS m−1) but a lower Δ than Moonlight and NorthStar at 11.0 dS m−1 salinity. The great reduction in Δ of P105 as salinity increased suggests that salinity induced a greater degree of stomatal resistance that provided less opportunity for discrimination against the heavier isotope. Carbon isotope discrimination may serve as a useful selection criterion in breeding efforts to develop salt tolerant KBG.