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Gas exchange and water relations responses to warming were compared for two shrub species, Artemisia tridentata spp. vaseyana (Asteraceae), a widely distributed evergreen species of the Great Basin and the western slope of the Rocky Mountains, and Pentaphylloides floribunda (Rosaceae), a deciduous shrub limited in distribution to moist, high-elevation meadows. Plants were exposed to an in situ infrared (IR) climate change manipulation at the Rocky Mountain Biological Laboratory, near Crested Butte, CO. Measurements of gas exchange and water relations were made on the two species in July and August, 1993 from plants growing in situ in infrared-heated and control plots. Carbon dioxide uptake, water loss, leaf temperature,...
Deuterated water absorbed by deep roots of Artemisia tridentata appeared in the stem water of neighboring Agropyron desertorum tussocks. This supports the hypothesis that water absorbed by deep roots in moist soil moves through the roots, is released in the upper soil profile at night, and is stored there until it is resorbed by roots the following day. This phenomenon is termed hydraulic lift. The potential for parasitism of the water stored in the upper soil layers by neighboring plant roots is also shown. The effectiveness of water absorption by deep roots was substantially improved with hydraulic lift as indicated by reductions of 25 to 50% in transpiration on days following experimental circumvention of hydraulic...
Early succession aspen and late succession conifer forests have different architecture and physiology affecting hydrologic transfer processes. An evaluation of water pools and fluxes was used to determine differences in the hydrologic dynamics between stands of quaking aspen (Populus tremuloides) and associated stands of mixed conifer consisting of white fir (Abies concolor), Douglas-fir (Pseudotsuga menziesii), and Engelmann spruce (Picea engelmannii). In 2005 and 2006, measurements of snow water accumulation, snow ablation (melt), soil water content, snowpack sublimation, and evapotranspiration (ET) were measured in adjacent aspen and conifer stands. Peak snow water equivalent (SWE) averaged 34–44% higher in...
In the sagebrush/bunchgrass steppe of the North American Great Basin soil water potential has been shown to exhibit diel fluctuations with water potential increasing during the night as a result of water loss from roots in relatively dry soil layers. We hypothesized that environmental conditions promoting low transpiration rates (shading, cloudiness) would cause a net increase in soil water potential as a result of reduced soil water depletion during the day and continuing water efflux from roots during the night. We examined the response of soil water potential to artificial shading in sagebrush/bunchgrass plantings and used a simple model to predict how soil water potential should respond to reduced transpiration....
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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 piñon) 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,...
Numerous basins of the intermountain area often have extensive playa surfaces that are nearly devoid of vegetation. Margins of these playas support sparse communities dominated by chenopod shrubs Allenrolfea occidentalis (iodine bush) and Sacrobatus vermiculatus (black greasewood). These plants establish and persist in an environment where halomorphic soils induce extreme osmotic stress and atmospheric precipitation is very low and erratic and occurs largely during the winter when temperatures are too low for growth. We measured net CO2 assimilation rates, leaf conductances, transpiration rates, water-use efficiencies, and stem xylem potentials for these two C3 species. Data were collected in above-average (1991)...
Continually rising atmospheric CO2 concentrations and possible climatic change may cause significant changes in plant communities. This study was undertaken to investigate gas exchange in two important grass species of the short-grass steppe, Pascopyrum smithii (western wheat-grass), C3, and Bouteloua gracilis (blue grama), C4, grown at different CO2 concentrations and temperatures. Intact soil cores containing each species were extracted from grasslands in north-eastern Colorado, USA, placed in growth chambers, and grown at combinations of two CO2 concentrations (350 and 700 ?mol mol?1) and two temperature regimes (field average and elevated by 4�C). Leaf gas exchange was measured during the second, third and fourth...
Growth of vegetative and reproductive structures in Artemisia tridentata is temporally separated during the growing season; vegetative growth occurs during spring and early summer when soil moisture is most abundant, while reproductive growth occur during summer and fall when soil moisture may be limiting. Vegetative and reproductive structures may therefore exhibit contrasting efficiencies of resource acquisition and investment resulting from temporal differences in resource availability during their development. We examined the effect of water stress on growth, photosynthesis, and resource investment for vegetative and reproductive modules of Artemisia tridentata by applying supplemental water. No differences...
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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...
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,...
1. Microclimate was measured and photosynthetic responses to a climate warming manipulation were compared for the evergreen shrub Artemisia tridentata and the herbaceous forb Erigeron speciosus in the Rocky Mountains, Colorado, USA. 2. Soil was warmer and drier under infra-red heaters compared with control plots. 3. Midday xylem pressure potential did not differ for A. tridentata on heated vs control plots but was lower for E. speciosus on heated plots compared with controls. Leaf temperatures did not vary for the two species on heated or control plots. 4. There were no significant treatment or species differences in the diurnal patterns of CO2 assimilation or stomatal conductance to water vapour. Also, there were...
Quaking aspen cover 3.3 million hectares in the Upper Colorado River Basin, and these areas are gradually converting to conifer forest by the natural process of ecological succession. This change is being hastened by forest managment practices that reduce fires, destroy pests, or otherwise prevent the natural processes that previously caused conifer areas to revert to the subclimax aspen. The hydrologic consequence has been forecast to cause a runoff reduction in the Colorado River as large as one million acre-feet annually, a major blow to water availability in the Lower Basin. Understanding and dealing with the problems requires quantitative comparision of the evaportranspiration rates of conifer and aspen forests...
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,...
Water availability defines and is the most frequent control on processes in arid and semiarid ecosystems. Despite widespread recognition of the importance of water in dry areas, knowledge about key processes in the water balance is surprisingly limited. How water is partitioned between evaporation and transpiration is an area about which ecosystem ecologists have almost no information. We used a daily time step soil water model and 39 years of data to describe the ecohydrology of a shortgrass steppe and investigate how manipulation of soil and vegetation variables influenced the partitioning of water loss between evaporation and transpiration. Our results emphasize the overwhelming importance of two environmental...
    map background search result map search result map The influence of shade and clouds on soil water potential: The buffered behavior of hydraulic lift Ecohydrology in a Colorado River riparian forest: implications for the decline of Populus fremontii Seasonal variations in moisture use in a pinon-juniper woodland. Ecohydrology in a Colorado River riparian forest: implications for the decline of Populus fremontii Seasonal variations in moisture use in a pinon-juniper woodland.