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United States Department of Agriculture

Agricultural Research Service

Title: Carbon Isotope Discrimination and Forage Yield of 14 Cool-Season Perennial Grasses Across An Irrigation Gradient

Authors
item Asay, Kay
item Johnson, Douglas
item Jensen, Kevin

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 24, 2002
Publication Date: September 24, 2002
Citation: Johnson, D.A., K.H. Asay, and K.B. Jensen. 2003. Trends in Carbon Isotope Discrimination and Forage Yield of 14 Cool-Season Perennial Grasses across an Irrigation Gradient. J. Range Manage. 56: 654-659.

Interpretive Summary: To be productive and persist on grazing lands in western North America perennial grasses must be tolerant of drought and make efficient use of limited water resources. Carbon isotope discrimination in plant leaves has been negatively associated with water-use efficiency (WUE) in cool- season grasses. We established 14 cool-season, perennial grasses in a facility that allowed us to control the amount of water received by the individual plots. Objectives were to study: 1) trends in CID and dry matter yield (DMY) at different levels of irrigation, 2) relative differences among these grasses at each water level, and 3) the relationship between DMY and CID. When aveeraged across years, grasses differed significantly for CID at the highest and lowest water levels and CID tended to decrease in a near linear manner from the highest to lowest water level. Although some inconsistencies were evident, the trends for CID were similar for all grasses studied. Grass entries also differed significantly for DMY at each of six water levels. Dry matter yield decreased linearly from high to low water levels; however the trend was not consistent among the grasses. The correlations between CID & DMY were consistently positive but significant in only a few instances. We conclude that differences among these perennial, cool-season grasses were more stable for CID than DMY across irrigation levels, and that the grasses made more efficient use of water under more xeric conditions. In general, CID was not closely associated with DMY; however, exceptions with high DMY and high CID (low WUE) also were evident.

Technical Abstract: Grasses used on grazing lands in western North America must make efficient use of limited water resources. Selection for carbon isotope discrimination has shown potential for improving water-use efficiency (WUE) in cool-season grasses. Fourteen cool-season, perennial grasses (12 from Triticeae, 1 from Bromeae, and 1 from Poeae tribes) were established in a rainout shelter facility, and a line- source irrigation system was to used to study: i) trends in CID across three water levels (WL-1, 3, and 5) and dry matter yield (DMY) across six water levels (WL-1 through 6), ii) grass entry x water level interactions for these traits, and iii) the relationship of DMY and CID. When averaged across years, entries differed significantly for CID at the highest (WL-1) and lowest (WL-5) water levels. Values of CID decreased in a near linear manner from WL-1 to WL-5, and although some inconsistencies were evident, the trend was similar for all entries. Entries also differed significantly for DMY at each of six water levels. Although the change in DMY was mostly linear across water levels, the trend was not consistent among entries. The correlations between CID and DMY were consistently positive but significant only at WL-3 (r = 0.54, P < 0.5), and between CID at WL-5 and DMY at WL-3 (r = 0.60, P < 0.05). We conclude that differences among these perennial, cool-season grasses were more stable for CID than DMY across irrigation levels, and that the grasses made more efficient use of water under more xeric conditions. In general, CID was not closely associated with DMY; however, exceptions with high DMY and high CID (low WUE) also were evident.

Last Modified: 11/21/2014
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