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ARS Home » Pacific West Area » Logan, Utah » Forage and Range Research » Research » Publications at this Location » Publication #126959
Title: CARBON ISOTOPE DISCRIMINATION OF TALL FESCUE CULTIVARS ACROSS AN IRRIGATIONGRADIENT

Author
item Asay, Kay
item Jensen, Kevin
item Johnson, Douglas
item Waldron, Blair

Submitted to: International Journal of Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2002
Publication Date: 10/16/2002
Citation: Jensen, K.B., Asay, K.H., D.A. Johnson, and B.L. Waldron. 2004. Carbon isotope discrimination in tall fescue cultivars across an irrigation gradient. Can. J. Plant Sci. 84: 157-162.

Interpretive Summary: Selection for more efficient use of water is an important objective in grass breeding programs in semiarid regions of western North America. Determination of carbon isotope discrimination has been proposed as an indirect method of evaluating WUE in cool-season grasses. Ten cultivars of tall fescue were established in the field under four levels of irrigation. Our objectives were to evaluate: (a) trends in carbon isotope discrimination across irrigation levels and (b) to study relationships between carbon isotope discrimination and dry matter yield (DMY) within and across irrigation levels. Consistent and significant differences were found among cultivars for carbon isotope discrimination when evaluated across two harvests at an intermediate level of irrigation intensity. Cultivars also differed significantly for carbon isotope discrimination across four irrigation levels when evaluated later in the season. Relative differences among cultivars were consistent across water levels. Although a nonlinear trend was evident for some cultivars, mean carbon isotope discrimination values decreased in a near linear manner from the high to low level of irrigation. Statistical analysis of the data showed that 95% of the variation across water levels was linear. Correlations between carbon isotope discrimination and DMY were not significant at the higher irrigation levels, but the correlations were positive at the drier levels. We conclude that tall fescue cultivars can be selected effectively for WUE on the basis of carbon isotope discrimination averaged across sampling dates and levels of water application. Plant breeders should be cautioned to avoid a decline in DMY that may accompany increased WUE.

Technical Abstract: Water-use efficiency (WUE) is an important criterion in the selection of grasses for irrigated pastures in semiarid regions of western North America. Carbon isotope discrimination has been proposed as an indirect criterion for evaluating WUE in cool-season grasses. Ten cultivars of tall fescue (Festuca arundinaceae Schreb.) were established in the field under a line-source irrigation system. Objectives of our two-year study were to evaluate: (i) trends in carbon isotope discrimination across a gradient of four water levels (WL-2, wettest to WL-5, driest) and (ii) relationships between carbon isotope discrimination and dry matter yield (DMY) within and across water levels. Consistent and significant differences (P < 0.05) were found among cultivars for carbon isotope discrimination when evaluated across two harvests at WL-2. Cultivars also differed significantly for carbon isotope discrimination (P < 0.01) across four water levels when evaluated at the later harvest date. As with harvest dates, relative differences among cultivars were consistent across water levels. Although a curvilinear trend was evident for some cultivars, mean carbon isotope discrimination values decreased in a near linear manner from WL-2 to WL-5. Based on orthogonal polynomials the mean trend across water levels was partitioned as 95% linear and 5% quadratic. Correlations between carbon isotope discrimination and DMY were nonsignificant at the wetter water levels (WL-2 and 3), but the correlations were positive at the drier levels (WL-4 and 5). We conclude that tall fescue cultivars can be selected effectively for WUE on the basis of carbon isotope discrimination averaged across sampling dates.