Experimental study of carbon-isotope fractionation between diet, hair, and feces of mammalian herbivores

Journal ArticleThe carbon-isotope composition of hair and feces offers a glimpse into the diets of mammalian herbivores. It is particularly useful for determining the relative consumption of browse and graze in tropical environments, as these foods have strongly divergent carbon-isotope compositions. Fecal ?13C values reflect the last few days consumption, whereas hair provides longer term dietary information. Previous studies have shown, however, that some fractionation occurs between dietary ?13C values and those of hair and feces

Carbon isotope discrimination in the C4 shrub Atriplex confertifolia along a salinity gradient

Journal ArticleCarbon isotope discrimination (∆) was measured for leaves of Atriplex confertifolia along a salinity gradi~ ent in northern Utah. Over this gradient, the variation of ∆ values was high for a C4 species, and the ∆ values were positively correlated with salinity in both years of the study. Of the possible explanations for this pattern, the ∆ results are consistent with the notion that salinity induces an increase in the bundle sheath leakiness of these C4 plants

Sensitivity of the Colorado plateau to change: climate, ecosystems, and society

Journal ArticleThe Colorado Plateau is located in the interior, dry end of two moisture trajectories coming from opposite directions, which have made this region a target for unusual climate fluctuations. A multidecadal drought event some 850 years ago may have eliminated maize cultivation by the first human settlers of the Colorado Plateau, the Fremont and Anasazi people, and contributed to the abandonment of their settlements. Even today, ranching and farming are vulnerable to drought and struggle to persist. The recent use of the Colorado Plateau primarily as rangeland has made this region less tolerant to drought due to unprecedented levels of surface disturbances that destroy biological crusts, reduce soil carbon and nitrogen stocks, and increase rates of soil erosion

Orientation and slope preference in barrel cactus (Ferocactus acanthodes) at its northern distribution limit

Journal ArticleMicrosite distribution and diurnal tissue temperature fluctuations were measured in Ferocactus acanthodes (barrel cactus) at its northern distribution limit in the Beaver Dam Mountains of southwestern Utah. At this location, barrel cacti were limited to south-facing slopes. Orientation (azimuth and angle) of both the cactus stem and of the apical region at the top of the cactus were nonrandom, strongly facing south. The potential adaptive significance of this orientation in minimizing apical meristematic tissue damage under low wintertime conditions and minimizing high temperature damage under summertime conditions is discussed

Carbon isotope ratios in belowground carbon cycle processes

Journal ArticleAnalyses of carbon isotope ratios (δ13C) in soil organic matter (SOM) and soil respired CO2 provide insights into dynamics of the carbon cycle. δ13C analyses do not provide direct measures of soil CO2 efflux rates but are useful as a constraint in carbon cycle models. In many cases, δ13C analyses allow the identification of components of soil CO2 efflux as well as the relative contribution of soil to overall ecosystem CO2 fluxes

Carbon isotope dynamics in Abies amabilis stands in the Cascades

Journal ArticleCarbon isotope ratios (d13C) of canopy air and carbon isotope discrimination at the ecosystem level were studied in three montane Pacific silver fir (Abies amabilis (Dougl. ex Loud.) Dougl. ex J. Forbes) stands, an old-growth and two younger stands. Spatial and temporal variations of canopy CO2 concentrations ([CO2]) and their d13C were strongly related to stand structure. Within the old-growth stand, both daytime canopy [CO2] and canopy d13C stayed close to those of the troposphere, either indicating low overall photosynthetic rates or high turbulent mixing

Sourcing drugs with stable isotopes

ManuscriptCarbon (δ13C) and nitrogen (δ15N) isotope ratios at natural abundance levels are useful tools in determining the region-of-origin for both cocaine and heroin. Here we show that cocaine originating from different geographic regions of South America exhibited pronounced differences in their δ13C and δ15N values. The distinct isotope-ratio combinations allow reliable determination of the region-of-origin for the major coca growing regions along the Andean Ridge

Ecophysiology of riparian cottonwood and willow before, during, and after two years of soil water removal

Journal ArticleRiparian cottonwood/willow forest assemblages are highly valued in the southwestern United States for their wildlife habitat, biodiversity, and watershed protection. Yet these forests are under considerable threat from climate change impacts on water resources and land-use activities to support human enterprise. Stream diversions, groundwater pumping, and extended drought have resulted in the decline of cottonwood/willow forests along many riparian corridors in the Southwest and, in many cases, the replacement of these forests with less desirable invasive shrubs and trees. Nevertheless, ecophysiological responses of cottonwood and willow, along with associated ecohydrological feedbacks of soil water depletion, are not well understood. Ecophysiological processes of mature Fremont cottonwood and coyote willow stands were examined over four consecutive growing seasons (2004-2007) near Salt Lake City, Utah, USA. The tree stands occurred near the inlet of a reservoir that was drained in the spring of 2005 and remained empty until mid-summer of 2006, effectively removing the primary water source for most of two growing seasons. Stem sap flux density (Js) in cottonwood was highly correlated with volumetric soil moisture (h) in the upper 60 cm and decreased sevenfold as soil moisture dropped from 12% to 7% after the reservoir was drained. Conversely, Js in willow was marginally correlated with h and decreased by only 25% during the same period. Opposite patterns emerged during the following growing season: willow had a lower whole-plant conductance (kt) in June and higher leaf carbon isotope ratios (d13C) than cottonwood in August, whereas kt and d13C were otherwise similar between species. Water relations in both species recovered quickly from soil water depletion, with the exception that sapwood area to stem area (As:Ast) was significantly lower in both species after the 2007 growing season compared to 2004. Results suggest that cottonwood has a greater sensitivity to interannual reductions in water availability, while willow is more sensitive to longer periods of soil water depletion. These data shed light on the linkage between soil water deficits and ecophysiological processes of threatened riparian forests given potential land-use and long-term drought impacts on freshwater resources

Burning coal seams in southern Utah: a natural system for studies of plant responses to elevated CO2

Book ChapterIn the Burning Hills and Smoky Mountains of southern Utah (USA), coal deposits exposed to the surface have been ignited by lightning and have been burning for periods of years to over a century. We examined one of these sites, where the below-ground combustion of this low-sulfur coal releases gases to the atmosphere from vents above the burning seam. The surrounding vegetation is cold-desert shrub, typical of the region and consisted of both C3 and C4 perennial species