title: The use of stable carbon isotope analysis in rooting studies.
abstract: Stable carbon isotope analysis was evaluated as a means of predicting the relative proportions of C3and C4root phytomass in species mixtures. The following mixtures of C3and C4species were used: 1) big bluestem (Andropogon gerardii)/cheatgrass (Bromus tectorum), 2) little bluestem (Schizachyrium scoparium)/cheatgrass, and 3) sorghum (Sorghum bicolor)/sunflower (Helianthus annuus). There was a significant correlation (P<0.01) between % C4phytomass and stable carbon isotope values for each of the three combinations (r2>0.98). Root length per mass varied among the five species studied (10.1-94.3 m/g), which resulted in different conclusions depending on whether root values are expressed as length or mass. For example, field samples from a tallgrass prairie site were estimated to contain about 20% cheatgrass on a mass basis, whereas the figure was 68% when expressed in terms of length. The combination of stable carbon isotope analysis with length-for-mass measurements promises to be a useful means of studying root competition between C3and C4plants.
authors.affiliation: USDA/ARS Southwestern Livestock and Forage Research Laboratory, P.O. Box 1199, 73036, El Reno, OK, USA.
authors.forename: Tony J
authors.initials: TJ
authors.lastname: Svejcar
authors.affiliation: Stable Isotope Program, USDA/ARS Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, 77030, Houston, TX, USA.
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Boutton