Carbon Isotope Discrimination, Gas Exchange, and Water-Use Efficiency in Crested Wheatgrass Clones
1991
Read, John J. | Johnson, Douglas A. | Asay, Kay H. | Tieszen, Larry L.
Carbon isotope discrimination (Δ) has been proposed as a criterion in selecting for water-use efficiency (WUE) in C₃ crop species. This study was conducted to determine associations among Δ, leaf instantaneous WUE (WUEᵢ), and shoot WUE (WUE₃) in clones of crested wheatgrass [Agropyron desertorum (Fischer ex Link) Schultes] previously selected for low, medium, and high Δ. Nine clones (three in each Δ class) were grown in a greenhouse in pots weighed every third day and brought to either 0.03 or 0.12 kg kg⁻¹ gravimetric water content. Leaf gas exchange rates and water potentials were determined at 2-wk intervals until plant harvest at 12 wk. Under drought, the ranking of Δ classes for stomatal conductance agreed with previous and present Δ classifications, and midday leaf water potentials averaged ≈0.4 MPa lower in the low than in the medium or high Δ class. Shoot dry weight and Δ decreased with drought and were correlated positively under well-watered conditions (r = 0.77*, df = 7, P < 0.05), but not under drought. Although Δ and leaf intercellular CO₂ concentration of individual clones were correlated positively at each water level, the expected differences between Δ classes in Δ, WUEᵢ, and WUE₃ were obtained only under drought. A lower Δ in low than high Δ class under drought was associated with greater shoot dry weight, WUE₃, and WUEᵢ. Across water levels, large negative correlations were found between Δ and WUEᵢ (r = -0.95**, df = 16, P < 0.01) or WUE₃ (r = −0.89**, df = 16). These results indicate that selection for low carbon isotope discrimination will improve water-use efficiency in crested wheat-grass under drought. Joint contribution of the USDA-ARS, USDA-Cooperative States Res. Service (Grant no. 86-CSRS-2-2962), and the Utah Agric. Exp. Stn., Logan UT 84322-4810. Journal Paper no. 4065.
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