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Turgor maintenance, solute content and recovery from water stress were examined in the drought-tolerant shrub Artemisia tridentata. Predawn water potentials of shrubs receiving supplemental water remained above ?2 MPa throughout summer, while predawn water potentials of untreated shrubs decreased to ?5 MPa. Osmotic potentials decreased in conjunction with water potentials maintaining turgor pressures above 0 MPa. The decreases in osmotic potentials were not the result of osmotic adjustment (i.e. solute accumulation). Leaf solute contents decreased during drought, but leaf water volumes decreased more than 75% from spring to summer, thereby passively concentrating solutes within the leaves. The maintenance of positive...
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Larrea tridentata is a xerophytic evergreen shrub, dominant in the arid regions of the southwestern United States. We examined relationships between gasexchange characteristics, plant and soil water relations, and growth responses of large versus small shrubs of L. tridentata over the course of a summer growing season in the Chihuahuan Desert of southern New Mexico, USA. The soil wetting front did not reach 0.6 m, and soils at depths of 0.6 and 0.9 m remained dry throughout the summer, suggesting that L. tridentata extracts water largely from soil near the surface. Surface soil layers (max) occurred in early summer (21.3 � mol m-2 s-1), when pre-dawn xylem water potential (XWP) reached ca. -1 MPa. Although both...
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1. Windblown dust, an environmental problem in many disturbed arid lands, has the potential to affect the physiological performance of desert shrubs. Physiological parameters of gas exchange for three species (Larrea tridentata, Hymenoclea salsola and Atriplex canescens) were measured at a Mojave Desert site, at which both undisturbed and heavily dusted individual shrubs occurred. 2. Maximum rates of net photosynthesis (A) of dusted organs were reduced to 21% of those of control plants in resinous leaflets of Larrea, to 44% in resinous leaves and photosynthetic stems of Hymenoclea, and to 58% in non-resinous C4 leaves of Atriplex, which have vesiculated trichomes. Dusted plants of all three species showed reduced...
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Seedlings of the succulent crassulacean acid metabolism (CAM plant Agave deserti in the northwestern Sonoran Desert were found only in sheltered microhabitats, nearly all occurring under the canopy of a desert bunchgrass, Hilaria rigida. Apparently because soil surface temperatures can reach 71@?C in exposed areas, seedlings were generally located near the center or on the northern side of this nurse plant. Both species have shallow root systems, about half of the roots of H. rigida and all those for seedlings of A. deserti occurring above soil depths of 0.08 m. To examine competition for water between the nurse plant and an associated seedling, a three-dimensional model for root water uptake was developed. The...
The seasonality of Glomus fasciculatum associated with Bouteloua gracilis and Pascopyrum smithii was contrasted in the field, as well as the effects of this vesicular-arbuscular mycorrhizal (VAM) fungus on physiological parameters of these grasses in the greenhouse Arbuscule formation was earlier in P smithii, which has C3 photophysiology, than in the C1 B gracilis Soil spore densities were highest in fall samples of both grasses Both grasses exhibited lower stomatal resistance and increased photosynthesis with VAM formation, but these changes were 36% greater for B gracilis B gracilis has a greater percentage of VAM infection than P smithii in the field, but % of the root length infected in the two grasses was...
Severe droughts have been associated with regional-scale forest mortality worldwide. Climate change is expected to exacerbate regional mortality events; however, prediction remains difficult because the physiological mechanisms underlying drought survival and mortality are poorly understood. We developed a hydraulically based theory considering carbon balance and insect resistance that allowed development and examination of hypotheses regarding survival and mortality. Multiple mechanisms may cause mortality during drought. A common mechanism for plants with isohydric regulation of water status results from avoidance of drought-induced hydraulic failure via stomatal closure, resulting in carbon starvation and a cascade...
In order to better elucidate fixed-C partitioning, nutrient acquisition and water relations of prairie grasses under elevated [CO2], we grew the C4 grass Bouteloua gracilis (H.B.K.) lag ex Steud. from seed in soil-packed, column-lysimeters in two growth chambers maintained at current ambient [CO2] (350 ?L L?1) and twice enriched [CO2] (700 ?L L?1). Once established, plants were deficit irrigated; growth chamber conditions were maintained at day/night temperatures of 25/16�C, relative humidities of 35%/90% and a 14-hour photoperiod to simulate summer conditions on the shortgrass steppe in eastern Colorado. After 11 weeks of growth, plants grown under CO2 enrichment had produced 35% and 65% greater total and root...
Pressure-volume measurements were made on Artemisia tridentata Nutt. ssp. tridentata samples rehydrated for 0, 1.5, 3, 6 or 24 h. Increasing rehydration time caused a significant increase in osmotic potential at turgor loss, cell elasiticity, and the relative water content at turgor loss, and a significant decrease in pressure potential at saturation. Osmotic potential at saturation was changed significantly by rehydration, but no consistent trend was observed. The symplastic water fraction did not differ significantly among treatments. The increase in the osmotic potential at turgor loss did not correspond with decreasing cell elasticity or synthesis of solutes. Instead, the leaf solute content remained constant...
We conducted a field experiment to assess effects of simulated above-average fall and spring precipitation on monoculture performance and competitive relations of the exotic annual grass Bromus tectorum and the native bunchgrass Stipa hymenoides in southeastern Utah. Between 1 October 1997 and 31 May 1998, "wet" plots received 239 mm and "dry" plots received 119 mm of water representing 175 and 87 percent of average precipitation, respectively. In monoculture, added water increased fall Bromus establishment by a factor of 1.6 but did not affect fall or winter growth. Added water adversely affected Bromus growth during early spring, but enhanced growth as soils dried during mid-spring. Overall, Bromus shoot production...
* 1 In western North America, juniper trees (Juniperus spp.) are apparently encroaching into numerous communities including sagebrush-dominated (Artemisia tridentata) valleys, where, as density of juniper increases, the density and condition of sagebrush decline but juniper condition appears unaffected. * 2 We examined stable isotope proxies of plant gas exchange and relative depth of soil water extraction of Juniperus osteosperma and Artemisia tridentata as their relative densities changed across a transition zone in northern Utah, USA. Measurement of 13C and 18O of foliage allowed separation of the contributions of stomatal and biochemical factors to differences in mean intercellular CO2 concentration, while deuterium...
    map background search result map search result map Surface Dust Impacts on Gas Exchange in Mojave Desert Shrubs Interactions Between Seedlings of Agave Deserti and the Nurse Plant Hilaria Rigida Effects of plant size and water relations on gas exchange and growth of the desert shrub Larrea tridentata Shifts in depth of water extraction and photosynthetic capacity inferred from stable isotope proxies across an ecotone of Juniperus osteosperma (Utah juniper) and Artemisia tridentata (big sagebrush) Interactions Between Seedlings of Agave Deserti and the Nurse Plant Hilaria Rigida Effects of plant size and water relations on gas exchange and growth of the desert shrub Larrea tridentata Surface Dust Impacts on Gas Exchange in Mojave Desert Shrubs