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We contrasted the seasonal use of simulated large rain events (24 mm) by three native species of the arid Colorado Plateau: the perennial grass Hilaria jamesii and two shrubs Artemesia filifolia and Coleogyne ramosissima. Deuterium-enriched water was used to distinguish shallow "pulse" water from water in deeper soil layers that were unaffected by the water input. We also measured the leaf gas exchange rates of watered and unwatered control plants for 5 days after the rain event. H. jamesii had twice the pulse water proportion in its xylem than the two shrubs in spring (approx. 70% vs 35%). In summer, the pulse water proportions of all species were around 70%. The increase in the relative pulse water uptake of the...
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Historically, ecosystems in the southwestern United States derived much of their nitrogen (N) from N-fixation in biological soil crusts. Today, these regions have highly reduced crust cover, and atmospheric deposition may be the dominant source of N. This study investigates the effects of increased nitrogen deposition on nitrogen uptake, photosynthesis, and growth of the two main forage grasses on the Colorado Plateau, galleta (Hilaria jamesii [Torr.] Benth.) and Indian ricegrass (Oryzopsis hymenoides, [Roemer & J.S. Schultes] Ricker ex Piper). Plots were fertilized for 2 years with 0, 10, 20, and 40 kg nitrogen ha?1 annually, up to 4� the estimated current annual deposition rate, in 2 applications per year (spring...
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We conducted experiments to examine the quantitative relationships between rainfall event size and rainwater uptake and use by four common native plant species of the Colorado Plateau, including two perennial grasses, Hilaria jamesii (C(4)) and Oryzopsis hymenoides (C(3)), and two shrubs, Ceratoides lanata (C(3)), and Gutierrezia sarothrae (C(3)). Specifically, we tested the hypothesis that grasses use small rainfall events more efficiently than shrubs and lose this advantage when events are large. Rainfall events between 2 and 20 mm were simulated in spring and summer by applying pulses of deuterium-labeled irrigation water. Afterwards, pulse water fractions in stems and the rates of leaf gas exchange were monitored...
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The release of the saltcedar beetle (Diorhabda carinulata) has resulted in the periodic defoliation of tamarisk (Tamarix spp.) along more than 1000 river km in the upper Colorado River Basin and is expected to spread along many other river reaches throughout the upper basin, and possibly into the lower Colorado River Basin. Identifying the impacts of these release programs on tamarisk water use and subsequent water cycling in arid riparian systems are largely unknown, due in part to the difficulty of measuring water fluxes in these systems. We used lab-calibrated, modified heat-dissipation sap flux sensors to monitor tamarisk water use (n = 20 trees) before, during and after defoliation by the saltcedar leaf beetle...
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Leaf carbonisotope discrimination (?) was measured for three dominant, semi-arid woodland species along a summer monsoon gradient inthe southwestern United States over a 2-year period. We tested the hypothesis that decreased humidity levels during the growing season along this gradient resulted in lower leaf ? values. Sites of similar elevation along the transect were selected and the range in monsoon contribution to overall annual precipitation varied from 18 to 58%, while total annual precipitation differed by a maximum of only 25% across this gradient. Leaf ? values in Quercus gambelii were negatively correlated with ?, a seasonally-weighted estimate of the evaporative humidity gradient, suggesting that stomatal...
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We investigated the effects of winter and summer drought on plants of the Colorado Plateau in western North America. This winter-cold, summer-hot desert region receives both winter and summer precipitation. Droughts were imposed for two consecutive years using rainout shelters. Here, we examine drought effects on the hydrologic interactions between plants and soil. We chose three perennial species for this study, representing different rooting patterns and responsiveness to precipitation pulses: Oryzopsis hymenoides, a perennial bunch grass with shallow roots; Gutierrezia sarothrae, a subshrub with dimorphic roots; and Ceratoides lanata, a predominantly deep-rooted woody shrub. Drought effects on plant water status...
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Tamarisk (Tamarix spp.) has invaded riparian ecosystems throughout the Western United States, including significant portions of riparian ecosystems within U.S. National Parks and Monuments. Recently, the saltcedar leaf beetle (Diorhabda elongata) was released as a tamarisk biocontrol agent. Although initial releases have been monitored, no comprehensive program is currently in place to monitor the rapid spread of Diorhabda that has resulted from numerous subsequent releases by county and state agencies. Long term monitoring of tamarisk defoliation and its impacts on habitat and water resources is needed. This study examines the potential for using higher spatial resolution Advanced Spaceborne Thermal Emission and...
Mention the word ?isotopes? and most people will think of short-lived radioactive isotopes. Yet far more abundant than the radioactive forms and perhaps much more useful for ecological studies are the stable isotopes. Early interest in stable isotope analyses developed in the geological sciences, and their application in environmental biology has developed slowly until recently. Over the past few years, innovative applications of stable isotope analyses to studies of biological processes have been expanding rapidly, and there is every indication that stable isotope approaches will lead to major advances over the next decade in our understanding of physiological processes and fluxes through ecological systems. Studies...
In desert ecosystems a large proportion of water and nitrogen is supplied in rain-induced pulses. It has been suggested that competitive interactions among desert plants would be most intense during these pulse periods of high resource availability. We tested this hypothesis with three cold desert shrub species of the Colorado Plateau (Gutierrezia sarothrae, Atriplex confertifolia, and Chrysothamnus nauseosus), which differ in their distribution of functional roots. In a three-year field study we conducted a neighbor removal experiment in conjunction with simulated 25-mm precipitation events and the addition of a nitrogen pulse in either spring or summer. We measured predawn water potential (?), gas exchange, leaf...
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Seasonal changes in the hydrogen isotope ratios of xylem waters were measured to determine water sources used for growth in desert plants of southern Utah. While all species used winter-spring recharge precipitation for spring growth, utilization of summer rains was life-form dependent. Annuals and succulent perennials exhibited a complete dependence on summer precipitation. Herbaceous and woody perennial species simultaneously utilized both summer precipitation and remaining winter-spring precipitation, with herbaceous species much more reliant on the summer precipitation component. Several of the woody perennials exhibited no response to summer precipitation. Currently, precipitation in southern Utah is evenly...
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Populus fremontii (Fremont cottonwood) was once a dominant species in desert riparian forests but has been increasingly replaced by the exotic invasive Tamarix ramosissima (saltcedar). Interspecific competition, reduced flooding frequency, and increased salinity have been implicated in the widespread decline of P. fremontii. To elucidate some of the multiple and interacting mechanisms of this decline, we examined ecological processes in a control stand of P. fremontii along the Colorado River in Utah, USA, as well as a disturbed stand characterized by high groundwater salinity and invasion of T. ramosissima. Sap flux data showed that P. fremontii at the saline site experienced large reductions in afternoon canopy...
Analyses of carbon isotope ratios (?13C) in soil organic matter (SOM) and soil respired CO2 provide insights into dynamics of the carbon cycle. ?13C analyses do not provide direct measures of soil CO2 efflux rates but are useful as a constraint in carbon cycle models. In many cases, ?13C analyses allow the identification of components of soil CO2 efflux as well as the relative contribution of soil to overall ecosystem CO2 fluxes. ?13C values provide a unique tool for quantifying historical shifts between C3 and C4 ecosystems over decadal to millennial time scales, which are relevant to climate change and land-use change issues. We identify the need to distinguish between ?13C analyses of SOM and those of soil CO2...
Maize (Zea mays) was a primary food crop for aboriginal societies of the arid American Southwest. Water used for maize production in these arid zones could have come from precipitation and runoff during the summer monsoon, from perennial streams and springs, or from stored soil water fed by snowmelt. The oxygen stable isotope ratio (?18O) of summer and winter precipitation on the Colorado Plateau naturally differ by more than 10? providing a powerful tool for distinguishing winter- from summer-derived water sources used in cultivation of maize. We investigated whether variation in ?18O of potential source waters is preserved in the ?18O of cellulose (?18Ocellulose) of maize cobs by growing four aboriginal and one...
In water-limited environments of the intermountain region of North America, summer precipitation may play a role in the structure and function of aridland communities and ecosystems. This study examined the potential reliance on summer precipitation of two widespread, coexisting woody species in the southwestern United States, Pinus edulis Englmn. (Colorado pi�on) and Juniperus osteosperma (Torr) Little (Utah juniper). The current distributions of P. edulis and J. osteosperma are highly suggestive of different dependencies on summer rainfall. We hypothesized that P. edulis was dependent on summer precipitation, utilizing summer precipitation even during extremely dry summers, whereas J. osteosperma was not dependent,...
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The 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 multi-decadal 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...
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Carbon isotope discrimination (?) was measured for leaves of Atriplex confertifolia along a salinity gradient 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 study. Of the possible explanations for this patter, the ? results are consistent with the notion that salinity induces an increase in the bundle sheath leakiness of these C4 plants. Published in Western North American Naturalist, volume 55, issue 2, on pages 135 - 41, in 1995.
Analyses of the natural variation in stable isotopes of components of ecological systems have provided new insights into how these systems function across paleoecological to modern timescales and across a wide range of spatial scales. Isotope abundances of the molecules in biological materials and geochemical profiles are viewed as recorders that can be used to reconstruct ecological processes or to trace ecological activities. Here, we review key short-, medium- and long-term recording capacities of stable isotopes that are currently being applied to ecological questions. The melding of advances in genetics, biochemical profiling and spatial analysis with those in isotope analyses and modeling sophistication opens...
In water-limited environments of the intermountain region of North America, summer precipitation may play a role in the structure and function of aridland communities and ecosystems. This study examined the potential reliance on summer precipitation of two widespread, coexisting woody species in the southwestern United States, Pinus edulis Englmn. (Colorado pi�on) and Juniperus osteosperma (Torr) Little (Utah juniper). The current distributions of P. edulis and J. osteosperma are highly suggestive of different dependencies on summer rainfall. We hypothesized that P. edulis was dependent on summer precipitation, utilizing summer precipitation even during extremely dry summers, whereas J. osteosperma was not dependent,...
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South-eastern Utah forms a northern border for the region currently influenced by the Arizona monosoonal system, which feeds moisture and summer precipitation into western North America. One major consequence predicted by global climate change scenarios is an intensification of monosoonal (summer) precipitation in the aridland areas of the western United States. We examined the capacity of dominant perennial shrubs in a Colorado Plateau cold desert ecosystem of southern Utah, United States, to use summer moisture inputs. We simulated increases of 25 and 50 mm summer rain events on Atriplex canescens, Artemisia filifolia, Chrysothamus nauseosus, Coleogyne ramosissima, and Vanclevea stylosa, in July and September...


    map background search result map search result map Dominant cold desert plants do not partition warm season precipitation by event size Effects of Nitrogen Deposition on an Arid Grassland in the Colorado Plateau Cold Desert Differential Utilization of Summer Rains by Desert Plants Monosoonal precipitation responses of shrubs in a cold desert community on the Colorado Plateau Deuterium enriched irrigation indicates different forms of rain use in shrub/grass species of the Colorado Plateau Summer and winter drought in a cold desert ecosystem (Colorado Plateau) part I: effects on soil water and plant water uptake Carbon isotope discrimination in three semi-arid woodland species along a monsoon gradient Ecohydrology in a Colorado River riparian forest: implications for the decline of Populus fremontii Remote monitoring of tamarisk defoliation and evapotranspiration following saltcedar leaf beetle attack Sap flux-scaled transpiration by tamarisk (Tamarix spp.) before, during and after episodic defoliation by the saltcedar leaf beetle (Diorhabda carinulata) Carbon isotope discrimination in the C4 shrub Atriplex confertifolia along a salinity gradient Sensitivity of the Colorado Plateau to Change: Climate, Ecosystems, and Society Ecohydrology in a Colorado River riparian forest: implications for the decline of Populus fremontii Remote monitoring of tamarisk defoliation and evapotranspiration following saltcedar leaf beetle attack Dominant cold desert plants do not partition warm season precipitation by event size Effects of Nitrogen Deposition on an Arid Grassland in the Colorado Plateau Cold Desert Deuterium enriched irrigation indicates different forms of rain use in shrub/grass species of the Colorado Plateau Summer and winter drought in a cold desert ecosystem (Colorado Plateau) part I: effects on soil water and plant water uptake Carbon isotope discrimination in the C4 shrub Atriplex confertifolia along a salinity gradient Sap flux-scaled transpiration by tamarisk (Tamarix spp.) before, during and after episodic defoliation by the saltcedar leaf beetle (Diorhabda carinulata) Differential Utilization of Summer Rains by Desert Plants Monosoonal precipitation responses of shrubs in a cold desert community on the Colorado Plateau Carbon isotope discrimination in three semi-arid woodland species along a monsoon gradient Sensitivity of the Colorado Plateau to Change: Climate, Ecosystems, and Society