Morphology and growth variation of Agropyron Smithii RYDB. (western wheatgrass) at different salinity levels

The purpose of this study was to determine the morphology and growth responses of Agropyron smithii Rydb. To various saline environments as evaluated in the laboratory. Agropyron smithii Rydb. (Rosana) seeds were germinated, transplanted into nutrient solutions with NaCl concentrations of 0, 50, 100, 150, and 200 m M , and grown for 80 days. Plant height, length of culm, and number of culms per plant were significantly reduced by the presence of NaCl in the nutrient solutions. As the external NaCl concentrations increased, values of root and plant ratio and leaf dry/fresh mass ratio increased significantly; biomass decreased significantly. However, the stomatal index, number of leaves per culm, and ratio of leaf length to leaf width were not significantly affected by the presence of NaCl.     

Ecological classification and monitoring model for the Wyoming big sagebrush shrubsteppe habitat type of northeastern Wyoming

The purposes of this study were to develop a multivariate statistical model related to plant succession, to classify by seral stage, and to monitor succession in Wyoming big sagebrush shrubsteppe habitat ( Artemisia tridentata ssp. wyomingensis / Agropyron smithii–Bouteloua gracilis ) in Thunder Basin National Grassland, Wyoming. This model can be used by range and wildlife managers to evaluate management alternatives by assessing changes in plant species cover and composition within and between seral stages. Four ecological seral stages that represent early to late succession were quantitatively identified with an estimated 92% accuracy. Three key plant species provided the necessary information to define seral stages and monitor trends. Percent canopy cover and percent frequency (used to calculate index values: % canopy cover × % frequency of occurrence) of Wyoming big sagebrush ( Artemisia tridentata ssp. wyomingensis ), western wheatgrass ( Agropyron smithii ), and blue grama ( Bouteloua gracilis ) are the only field measurements required for this model.     

Seasonal nutrient cycling in Potamogeton pectinatus of the lower Provo River

A common submersed aquatic plant of Great Basin wetland and riverine systems, Potamogeton pectinatus L. (sago pondweed) is a key waterfowl food. Nutritional qualities of submersed aquatics in the Great Basin are little understood. The purpose of this study was to determine the seasonal element cycling and nutritional qualities of P. pectinatus drupelet, leaf, and root tissues from the lower Provo River. Leaf tissues protein was 27% (dry weight) in July, but declined to 15% by December. Drupelet protein content was 9% in July and 6.5% in October. Lignocellulose in leaf tissue was lowest in July at 34% and increased as the season progressed. Percent fat was highest in leaf tissue at 12% in July. Sugars were highest in P. pectinatus leaf tissues in December and July. Calcium and magnesium concentrations increased in P. pectinatus tissues over the entire season. Leaf tissue zinc was 329 ppm (dry weight) in October. Leaf iron concentration was highest in September at 1184 ppm, while root tissue iron was 7166 ppm. Manganese content in leaf tissue peaked in October at 4990 ppm. Copper concentrations in leaves and roots were variable. High protein in leaf tissue would benefit local nesting and brooding waterfowl populations that feed on this aquatic. Trace metal concentrations in leaf and root tissues, from possible anthropogenic activities, appear very high during fall migratory months. Metal bioaccumulation by this species in other Great Basin wetlands and possible metal toxicity in waterfowl warrant further study.     

Nitrogen acquisition from different spatial distributions by six Great Basin plant species

Plants of different growth form may utilize soil nutrients in various spatial distributions through different scales of foraging. In this study we evaluated the ability of 6 species commonly found in the Great Basin to utilize nitrogen (N) distributed in different patterns. Three growth forms were represented by these 6 species. We applied 15 N-labeled nitrogen in concentrated patches and over broader uniform areas (at approximately 1% the concentration of the patches) in large, outdoor sand-culture plots. Six weeks after N was applied, 2 plants adjacent to the patch (Patch Treatment) and 2 plants within the uniform application (Uniform Treatment) were harvested. One plant 35-45 cm from both applications (Distant Treatment) was also harvested. The proportion of application-derived N in the leaf N pool was calculated and the mass of N this represented was estimated. Winter annual species Aegilops cylindrical and Bromus tectorum utilized the concentrated patches to a greater extent than did perennial species. The mass of N acquired by Patch-Treatment annual plants was significantly greater than by Uniform- and Distant-Treatment plants. Annual plants in the Distant Treatment had very little application-derived N in their leaf tissue. The perennial tussock grasses Agropyron desertorum and Pseudoroegneria spicata differed in utilization of the N applications. Agropyron acquired a greater quantity of N from patches than from uniform applications, and Distant- Treatment plants acquired very little from treatment applications. On the other hand, Pseudoroegneria utilized N in the 3 treatments equally. The shrub species Artemisia tridentata ssp. vaseyana and Chrysothamnus nauseosus also differed in their pattern of N acquisition. There were no differences in quantity of N acquired by plants from different treatments for Chrysothamnus ; all treatment plants acquired appreciable amounts of N from the applications. In contrast, Artemisia tridentata was very effective at acquiring large quantities of N from patches relative to Uniform- and Distant-Treatment plants, and yet there was still appreciable acquisition of applied N by Distant-Treatment Artemisia plants. We compared our results for these species in utilizing N patches with their ability to utilize N pulses (Bilbrough and Caldwell 1997). The annual grasses, Artemisia , and Agropyron were capable of effectively acquiring N from both pulses and patches, whereas Pseudoroegneria was effective in exploiting pulses but not patches. Chrysothamnus was generally not responsive to either patches or pulses. Our results suggest that the 2 shrubs and 2 perennial grasses differed in the scale at which they foraged for nutrients. Some species exhibited a coarse-scale utilization of nutrients while others were clearly capable of fine-scale utilization of spatially distributed nutrient sources. This suggests the potential for at least some spatial niche separation among these species.     

Big sagebrush ( Artemisia tridentata vaseyana ) and longleaf snowberry ( Symphoricarpos oreophilus ) plant associations in northeastern Nevada

Artemisia tridentata/Symphoricarpos oreophilus and Symphoricarpos oreophilus/Artemisia tridentata  plant associations were studied in northeastern Nevada. A 60-stand reconnaissance followed by a detailed study of 37 stands differentiated five important habitat types using an association table approach. Data reduction with DECORANA and TWINSPAN also described five plant associations that were differentiated by species occurrence and geographical distribution. All stands were found at elevations between 2,200 and 3,100 m in areas where snow accumulates and is late to melt. Stands are found on 15 families of soils that are relatively deep, often skeletal, dark colored, and productive. The dominant perennial grasses included Agropyron spicatum, Agropyron trachycaulum, and Festuca idahoensis.     

Field study of plant survival as affected by amendments to bentonite spoil

Efforts to reclaim amended and raw bentonite spoils with six plant species (two forbs, three shrubs, and one tree) were evaluated over a 4-year period. Plant species included fourwing saltbush ( Atriplex canescens [Pursh] Nutt.), big sagebrush ( Artemisia tridentata tridentata Nutt.), Rocky Mountain Juniper ( Juniperus scopulorum Sarg.), Russian olive ( Elaeagnus angustifolia L.) common yarrow ( Achillea millifolium L.) and scarlet globemallow ( Sphaeralcea coccinea [Pursh] Rydb.). Spoil treatments included addition of gypsum, sawdust, perlite, straw, and vermiculite; the control treatment was amended. Fourwing saltbush had 52% survival across all spoil treatments, with greatest survival occurring on perlite-treated spoil (80%), followed by gypsum (70%) and vermiculite amendments (70%). Survival of other plant species ranged from 0 to 2% averaged across all treatments after 4 years. No differences in plant survival occurred among amendments when all species were considered.     

Depletion of soil moisture by two cold-desert bunchgrasses and effects on photoshythetic performance

This study compared the abilities of two cool-season bunchgrasses to extract moisture from a drying soil and compared photosynthetic and stomatal responses of the two species as soil moisture supplies were depleted. When grown in 49-L pots in a greenhouse, Leymus cinereus extracted more water from the soil and maintained higher gas exchange rates to lower absolute amounts of soil water than did Agropyron desertorum . The soil water content at the lower limit of extraction was 10.3% for L. cinereus and 13.3% for A. desertorum . When soil moisture was expressed as extractable soil water, there was little difference between the species in pattern of water use. Both species maintained high stomatal conductances (g w ) and photosynthetic rates (A) until extractable soil moisture was reduced to about 15%. For field-grown plants under severe water stress, A was higher in L. cinereus than in A. desertorum at comparable leaf water potentials. The relationship between A and g w was similar for the two species; higher A in L. cinereus was a consequence of higher g w . Thus, higher A in L. cinereus is achieved through some sacrifice of water-use efficiency.     

Effect of salinity on seed germination of Triglochin maritima under various temperature regimes

Triglochin maritima L. (arrow grass), an herbaceous perennial in the family Juncaginacea, is widely distributed in inland and coastal salt marshes of North America. Triglochin maritima seeds from a population growing in a salt marsh at Faust, Utah, were germinated at 4 temperature regimes (12-h night/12-h day, 5-15° C, 10-20° C, and 15-25° C) and 5 salinities (0, 100, 200, 300, 400, and 500 mol m -3 NaCl) to determine optimal conditions for germination and level of salt tolerance. Ungerminated seeds were returned to distilled water after 20 d to determine whether seeds could recover from salinity treatments. Maximum germination occurred in distilled water, and increases in NaCl concentration progressively inhibited seed germination. No seeds germinated at concentrations higher than 400 mol m -3 NaCl. A temperature regime of low night (5° C) and high day (25° C) temperature yielded maximum germination; all other temperature regimes significantly inhibited seed germination relative to this optimum. Recovery of germination was highest at 5-25° C and lowest at 5-15° C. Recovery of seed germination when seeds were transferred to distilled water from salt solutions was highest at 5-25° C (72%) for seeds exposed to the 500 mol m -3 NaCl pretreatment and significantly reduced at other temperature regimes. The recovery germination response indicates a synergistic inhibitory interaction effect on germination when seeds were exposed to high salinities at suboptimal thermoperiods.     

Physiological, Morphological, and Environmental Variation Among Geographically Isolated Cottonwood (Populus Deltoides) Populations in New Mexico

The ability of a plant population to respond and eventually adapt to environmental stress ultimately determines that population's survival. This becomes especially significant in environments where important plant resource levels have radically decreased. Southwestern riparian areas have numerous plant species that are experiencing radical changes in water availability due to construction of dams, and thus their ability to respond to such changes is critical. One such species likely to be greatly affected by these hydrological changes is Populus deltoides var. wislizenii (cottonwood) because it relies heavily on both groundwater and river surface volume as primary water sources. Both water sources have been extremely impacted by impoundments along southwestern rivers. To understand how New Mexico populations of cottonwood may respond to environmental changes, we quantified environmental differences and characterized physiological and morphological variation among 4 cottonwood populations. Significant differences among study sites in water availability were indicated by both soil and groundwater salinity. The northernmost site, at Abiquiu, had the highest salinity levels in both soil and groundwater, followed by Bernardo, while San Antonio and Corrales sites had the lowest soil salinity. As expected, variation in physiological and leaf morphological characters existed among and within the tree populations, most likely in response to environmental factors. Midday xylem pressure potentials indicated that Abiquiu individuals suffered the greatest water stress and they also had the highest transpiration levels. Because of high specific leaf weights and high photosynthetic levels, cottonwoods at Corrales may better mitigate lower water availability. Such physiological and morphological trait variability among populations is ecologically important and may be of use in present reclamation and conservation efforts in these areas.     

New taxa and combinations in the Utah flora

New taxa include: Cryptantha cinerea (Torr.) Cronq. var. arenicola Higgins & Welsh; Physaria chambersii Rollins var. sobolifera Welsh (Cruciferae); Phacelia demissa Gray var. minor N. D. Atwood (Hydrophyllaceae); Iris pariensis Welsh (Iridaceae); Astragalus preussii var. cutleri Barneby and Pediomelum aromaticum (Payson) Welsh var. tuhyi Welsh (Leguminosae); Abronia nana Wats. var. harrisii Welsh (Nyctaginaceae); Camissonia atwoodii Cronq. (Onagraceae); Habenaria zothecina Higgins & Welsh (Orchidaceae); Aqiiilegia formosa Fisch. in DC. var. fosteri Welsh (Ranunculaceae). New nomenclatural combinations include: Rhus aromatica Ait. var. simplicifolia (Greene) Cronq. (Anacardiaceae); Lomatium kingii (Wats.) Cronq., L. kingii var. alpinum (Wats.) Cronq. (Apiaceae); Cryptantha cinerea (Torr.) Cronq. var. laxa (Macbr.) Higgins; Mertensia lanceolata (Pursh) DC. var. nivalis (Wats.) Higgins (Boraginaceae); Opuntia erinacea Engelm. var. aurea (Baxter) Welsh (Cactaceae); Arenaria fendleri Gray var. aculeata (Wats.) Welsh, A. fendleri var. eastwoodiae (Rydb.) Welsh, Lychnis apetala L. var. kingii (Wats.) Welsh, Stellaria longipes Goldie var. monantha (Hulten) Welsh (Caryophyllaceae); Draba densifolia Nutt. ex T. & G. var. apiculata (C. L. Hitchc.) Welsh, D. oligosperma Hook. var. juniperina (Dorn) Welsh, Physaria acutifolia Rydb. var. stylosa (Rollins) Welsh, Thelypodiopsis sagittata (Nutt.) Schulz var. ovalifolia (Rydb.) Welsh (Cruciferae); Lotus plebeius (T. Brandg.) Barneby, Lupinus polyphyllus Lindl. in Edwards var. ammophilus (Greene) Barneby, L polyphyllus var. humicola (A. Nels.) Barneby, L. argenteus Pursh var. fulvomaculatus (Payson) Barneby, L. argenteus var. palmeri (Wats.) Barneby, Pediomelum aromaticum (Payson) Welsh, P. epipsilum (Barneby) Welsh, Psoralidium lanceolatum (Pursh) Rydb. var. stenophyllum (Rydb.) Welsh, and P. lanceolatum var. stenostachys (Rydb.) Welsh (Leguminosae); Mirabilis linearis (Pursh) Hiemerl var. decipiens (Standl.) Welsh (Nyctaginaceae); Camissonia boothii var. condensata (Munz) Cronq., C. boothii var. villosa (Wats.) Cronq., C. clavaeformis (Torr. & Frem.) Raven var. purpurascens (Wats.) Cronq., C. scapoidea (T. & G.) var. utahensis (Raven) Welsh, Oenothera caespitosa var. macroglottis (Rydb.) Cronq., Oe. caespitosa var. navajoensis (Wagner, Stockhouse, & Klein) Cronq., Oe. flava (A. Nels.) Garrett var. acutissima (W. L. Wagner) Welsh, and Oe. primiveris Gray var. bufonis (Jones) Cronq. (Onagraceae); Papaver radicatum Rottb. var. pygmaeum (Rydb.) Welsh (Papaveraceae); Dodecatheon pulchellum (Raf.) Merr. var. zionense (Eastw.) Welsh (Primulaceae); Aquilegia flavescens Wats. var. rubicunda (Tidestr.) Welsh, Delphinium andersonii Gray var. scaposum (Greene) Welsh, D. occidentalis (Wats.) Wats. var. barbeyi (Huth) Welsh, and Ranunculus andersonii Gray var. juniperinus (Jones) Welsh (Ranunculaceae); Purshia mexicana (D. Don) Welsh and P. mexicana var. stansburyi (Torr.) Welsh (Rosaceae); Galium mexicanum H.B.K. var. asperrimum (Gray) Higgins & Welsh (Rubiaceae); Castilleja parvula Rydb. var. revealii (N. Holmgren) N. D. Atwood and C. rhexifolia Rydb. var. sulphurea (Rydb.) N. D. Atwood (Scrophulariaceae).     

Utah plant types—historical perspective 1840 to 1981—annotated list, and bibliography

New taxa include: Cryptantha cinerea (Torr.) Cronq. var. arenicola Higgins & Welsh; Physaria chambersii Rollins var. sobolifera Welsh (Cruciferae); Phacelia demissa Gray var. minor N. D. Atwood (Hydrophyllaceae); Iris pariensis Welsh (Iridaceae); Astragalus preussii var. cutleri Barneby and Pediomelum aromaticum (Payson) Welsh var. tuhyi Welsh (Leguminosae); Abronia nana Wats. var. harrisii Welsh (Nyctaginaceae); Camissonia atwoodii Cronq. (Onagraceae); Habenaria zothecina Higgins & Welsh (Orchidaceae); Aqiiilegia formosa Fisch. in DC. var. fosteri Welsh (Ranunculaceae). New nomenclatural combinations include: Rhus aromatica Ait. var. simplicifolia (Greene) Cronq. (Anacardiaceae); Lomatium kingii (Wats.) Cronq., L. kingii var. alpinum (Wats.) Cronq. (Apiaceae); Cryptantha cinerea (Torr.) Cronq. var. laxa (Macbr.) Higgins; Mertensia lanceolata (Pursh) DC. var. nivalis (Wats.) Higgins (Boraginaceae); Opuntia erinacea Engelm. var. aurea (Baxter) Welsh (Cactaceae); Arenaria fendleri Gray var. aculeata (Wats.) Welsh, A. fendleri var. eastwoodiae (Rydb.) Welsh, Lychnis apetala L. var. kingii (Wats.) Welsh, Stellaria longipes Goldie var. monantha (Hulten) Welsh (Caryophyllaceae); Draba densifolia Nutt. ex T. & G. var. apiculata (C. L. Hitchc.) Welsh, D. oligosperma Hook. var. juniperina (Dorn) Welsh, Physaria acutifolia Rydb. var. stylosa (Rollins) Welsh, Thelypodiopsis sagittata (Nutt.) Schulz var. ovalifolia (Rydb.) Welsh (Cruciferae); Lotus plebeius (T. Brandg.) Barneby, Lupinus polyphyllus Lindl. in Edwards var. ammophilus (Greene) Barneby, L polyphyllus var. humicola (A. Nels.) Barneby, L. argenteus Pursh var. fulvomaculatus (Payson) Barneby, L. argenteus var. palmeri (Wats.) Barneby, Pediomelum aromaticum (Payson) Welsh, P. epipsilum (Barneby) Welsh, Psoralidium lanceolatum (Pursh) Rydb. var. stenophyllum (Rydb.) Welsh, and P. lanceolatum var. stenostachys (Rydb.) Welsh (Leguminosae); Mirabilis linearis (Pursh) Hiemerl var. decipiens (Standl.) Welsh (Nyctaginaceae); Camissonia boothii var. condensata (Munz) Cronq., C. boothii var. villosa (Wats.) Cronq., C. clavaeformis (Torr. & Frem.) Raven var. purpurascens (Wats.) Cronq., C. scapoidea (T. & G.) var. utahensis (Raven) Welsh, Oenothera caespitosa var. macroglottis (Rydb.) Cronq., Oe. caespitosa var. navajoensis (Wagner, Stockhouse, & Klein) Cronq., Oe. flava (A. Nels.) Garrett var. acutissima (W. L. Wagner) Welsh, and Oe. primiveris Gray var. bufonis (Jones) Cronq. (Onagraceae); Papaver radicatum Rottb. var. pygmaeum (Rydb.) Welsh (Papaveraceae); Dodecatheon pulchellum (Raf.) Merr. var. zionense (Eastw.) Welsh (Primulaceae); Aquilegia flavescens Wats. var. rubicunda (Tidestr.) Welsh, Delphinium andersonii Gray var. scaposum (Greene) Welsh, D. occidentalis (Wats.) Wats. var. barbeyi (Huth) Welsh, and Ranunculus andersonii Gray var. juniperinus (Jones) Welsh (Ranunculaceae); Purshia mexicana (D. Don) Welsh and P. mexicana var. stansburyi (Torr.) Welsh (Rosaceae); Galium mexicanum H.B.K. var. asperrimum (Gray) Higgins & Welsh (Rubiaceae); Castilleja parvula Rydb. var. revealii (N. Holmgren) N. D. Atwood and C. rhexifolia Rydb. var. sulphurea (Rydb.) N. D. Atwood (Scrophulariaceae).     

Carbon isotope discrimination and water relations of oak hybrid populations in southwestern Utah

The evergreen oak Quercus turbinella and the deciduous Q. gambelii form natural hybrids in southwestern Utah and northern Arizona. Hybrid individuals also are found in northern Utah in a region where only Q. gambelii currently exists, indicating that Q. turbinella has recently retreated southward. Our objectives were to (1) examine the ecophysiology of parental taxa and hybrids under natural conditions in southeastern Utah, and (2) investigate the level of integration between leaf carbon isotope discrimination (a synthetic gas exchange trait) and structural and chemical traits of leaves in morphologically variable hybrid populations. Leaf length, width, mass-to-area ratio (LMA, g m -2 ), and nitrogen concentration (N, g g -1 ) within 2 hybrid populations near New Harmony, Utah, were highly intercorrelated. Variation within the hybrid populations spanned mean values for these traits observed in parental taxa from adjacent ""pure"" populations of each species. Carbon isotope discrimination (Δ), an integrated measure of the ratio of intercellular to ambient CO 2 concentration, ranged from 16.1‰ to 19.6‰ within the 2 hybrid populations and was positively correlated with leaf nitrogen concentration and negatively correlated with LMA; individuals in hybrid populations with leaves resembling Q. gambelii had the highest leaf Δ and N concentrations and lowest LMA compared with leaves from plants that resembled Q. turbinella . CO 2 uptake is limited by stomatal conductance and possibly by mesophyll resistance to a greater extent in Q. turbinella phenotypes than in intermediate or Q. gambelii phenotypes. δD of stem xylem water (an indication of active rooting depth) and predawn water potential during the peak monsoon period in August were not correlated to leaf Δ values within the hybrid populations. Several individuals that were morphologically similar to Q. turbinella in the hybrid populations maintained high predawn water potentials and derived moisture from winter recharge that presumably was taken from deep soil layers. Apparently, a few adult individuals of the Q. turbinella phenotype in hybrid populations accessed water from deep in the soil profile, which enabled them to avoid summer drought. Reduced monsoonal activity may have been an important, but not the single, determinant of Q. turbinella s retreat from northern Utah during the recent Holocene.     

Utah flora: Malvaceae

This paper is the third in a series dealing with a revision of the flora of Utah. Treated herein are 9 genera and 23 species, including both commonly cultivated, escaped, and indigenous representatives. Proposed new taxa include Sphaeralcea grossulariifolia (H. and A.) Rydb. var. moorei Welsh, Sphaeralcea leptophylla (Gray) Rydb. var. janeae Welsh, and Sphaeralcea psoraloides Welsh.       

Relationship of western juniper stem conducting tissue and basal circumference to leaf area and biomass

The ability to measure leaf area and biomass on a plant community basis has many important ecological applications. These include quantification of gas exchange, use of water resources on the site, nutrient pools, and construction of models simulating production and resource allocation. To test a nondestructive technique for estimating leaf area and leaf biomass of western juniper ( Juniperus occidentalis Hook.), sapwood area and basal circumference were evaluated as predictors of total leaf biomass and leaf area. Nineteen trees, ranging in size from 9.0 to 263 cm in circumference, were destructively sampled. The entire leaf biomass was harvested and measured, and regression equations were developed. Both sapwood area and basal circumference significantly (P < .01) correlated with projected leaf area and leaf biomass (r values = 0.98).     

Leafhopper assemblages on native and reseeded grasslands in southwestern Montana

Using sweep samples, we surveyed leafhoppers (Homoptera: Cicadellidae) on grassland sites in the Gallatin Valley of Montana during 1988 and 1991. We sampled 12 sites representing 2 habitat types defined by their dominant plant species in an undisturbed state ( Stipa comata / Bouteloua gracilis and Festuca idahoensis / Agropyron spicatum ). At half of the sites the native plant communities were present, whereas the remainder had been reseeded with either Agropyron spicatum (to replace the S. comata / B. gracilis assemblage ) or Bromus inermis (to replace the F. idahoensis / A. spicatum assemblage). We found at least 66 species of leafhoppers among 44,428 adults collected. Seven taxa comprised 83% of all individuals collected: Doratura stylata (26%), Ceratagallia spp. (18%), Endria inimica (17%), Orocastus perpusillus (7%), Sorhoanus spp. (6%), Athysanella spp. (5%), and Psammotettix lividellus (4%). Sites with similar vegetation had broadly similar leafhopper assemblages, and assemblages differed most between the relatively xeric Stipa comata / Bouteloua gracilis sites and the more mesic sites dominated by Bromus inermis . The composition of a leafhopper assemblage at a site tended to be more similar to those on noncontiguous sites with the same overall vegetation than to those on contiguous sites with different vegetation. These patterns are likely related to the fact that many Cicadellidae are host specialists. In fact, variation in abundance of some of the most common leafhopper taxa on our sites was correlated with the percent cover of their known host plants. Our analyses of the leafhopper assemblages generally support the contention that terrestrial plant associations are among the more useful indicators of insect community composition.     

Ecophysiology of the temperate desert halophytes: Allenrolfea occidentalis and Sarcobatus vermiculatus

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 CO 2 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) and below-average (1992) precipitation years. Net CO 2 assimilation rates for Allenrolfea were statistically similar in 1991 and 1992 but in general declined for Sarcobatus in 1992. For both species, leaf conductances and leaf transpiration rates declined significantly from 1991 to 1992, with the decline greater for Sarcobatus . Water-use efficiencies doubled from 1991 to 1992 for both plant species. Predawn xylem water potentials were -2.2 and -3.3 MPa for Allenrolfea and -1.8 and -2.6 MPa for Sarcobatus by September 1991 and 1992, respectively. Afternoon xlem water potentials were -3.1 and -2.0 MPa for Allrolfea and -2.6 and -2.2 for Sarcobatus beginning in May 1991 and 1992, respectively. Xylem water potentials dropped to -5.0 MPa for Allenrolfea and -3.4 MPa for Sarcobatus by September for both 1991 and 1992. For Allenrolfea , in general, the total soil water potential within the zone of maximum root activity is more negative than the plant's predawn xylem potential, which suggests that the plant is partially phreatophytic and/or has a large capacitance due to its extensive woody root system.     

High nitrogen availability does not improve salinity tolerance in Sarcobatus vermiculatus

Natural and anthropogenic changes in basin lake levels in the western U.S. expose saline, alkaline substrates that are commonly colonized by shrubs in the Chenopodiaceae. On a chronosequence of recently exposed substrates at Mono Lake, California, Sarcobatus vermiculatus has greatest biomass accrual, seed production, seedling establishment, and leaf N at younger sites where soils are extremely saline and alkaline. These field observations and an understanding of the role of N-containing compatible solutes in salinity tolerance of halophytes led to our prediction that Na and N interactions stimulate Sarcobatus performance. To test this, we grew Sarcobatus juveniles for 2 years in the greenhouse at 4 levels of NaCl (5, 100, 300, and 450 mM) and 3 levels of N (0.04, 0.4, and 8 mM) in a randomized, complete-block design. Contrary to our expectations, high N availability did not induce salt-stimulated growth nor did it increase salinity tolerance in Sarcobatus . Increased N nutrition also had no significant effect on leaf cation ratios or selectivity. Plants grown at high salinity had significantly lower leaf K:Na, Ca:Na, and Mg:Na ratios than plants grown at lower salinity. However, plant selectivity for the macronutrient cations remained high, even at 450 mM NaCl. Without such high selectivity, the cation nutrition of Sarcobatus would decline to even lower levels, resulting in severe nutrient deficiencies. This study suggests that the ability of Sarcobatus to attain high leaf N, rather than an interaction between Na and N, enhances its performance at saline sites. In addition, the ability of Sarcobatus to maintain high macronutrient cation selectivity despite high salinity allows its distribution to extend to extremely saline and alkaline substrates in this arid system.