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  • Articles  (4)
  • Agropyron desertorum  (3)
  • 550 - Earth sciences
  • Humans
  • Life and Medical Sciences
  • 1995-1999  (4)
  • 1
    Electronic Resource
    Electronic Resource
    The effects of shading and N status on root proliferation in nutrient patches by the perennial grass Agropyron desertorum in the field (1995)
    Springer
    Oecologia 103 (1995), S. 10-16 
    Details
    ISSN: 1432-1939
    Keywords: Agropyron desertorum ; Roots ; Soil heterogeneity ; Nitrogen ; Shading
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Competition for light can affect exploitation of spatially heterogeneous soil resources. To evaluate the influence of shoot status on root growth responses in nutrient-rich soil patches, we studied the effects of shading and whole-plant nitrogen status on root growth in N-enriched and nonenriched patches by mature Agropyron desertorum plants growing in the field with below-ground competition. Roots in enriched patches had greater length to weight ratios (specific root length, SRL), indicating increased absorptive surface areas, compared with roots in control patches. Increased SRL was due to increased production and length of higher order laterals rather than morphological changes in roots of the same branching order. Although the pattern of root growth rates in patches was the same for shaded and unshaded plants, the magnitude of this response to enriched patches was damped by shading. Root relative growth rates (RGR) in N-enriched patches were reduced by more than 50% by short-term shading treatments (60% reduction in photosynthetic flux density), while root RGR in unenriched patches was unaffected by shading. Unexpectedly, plants with higher nitrogen status had greater root RGR in enriched patches than plants that had not received nitrogen supplement, again with no detectable effect on root RGR in the unenriched patches. Therefore, while both shading and plant N status affected the ability of roots to exploit enriched patches by proliferation, there was no stimulation or suppression of root growth in the unenriched, control patches. Thus, plants already under competitive pressure above ground for light and below ground for nutrients should be less able to rapidly respond to opportunities presented in nutrient patches and pulses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00328419
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  • 2
    Electronic Resource
    Electronic Resource
    A large ephemeral release of nitrogen upon wetting of dry soil and corresponding root responses in the field (1997)
    Springer
    Plant and soil 191 (1997), S. 291-299 
    Details
    ISSN: 1573-5036
    Keywords: Agropyron desertorum ; mycorrhizae ; nutrient release by rain ; root growth ; root nutrient uptake kinetics ; soil moisture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract To assess changes in soil nutrients, root growth and mycrorrhizal infection in response to rain events, a water pulse was applied to a very dry soil. Wetting of a dry soil in the Great Basin of the Western United States led to a striking pulse of available soil nitrate in a field plot, but available phosphate was not affected. This is the first field demonstration of this phenomenon in the Great Basin as far as we are aware. This pulse was only apparent for a few days, probably due to microbial immobilization of the nitrogen. Root ammonium uptake capacity increased within one day of the water pulse, but new root growth was not apparent until 3 days after the water pulse. Thus, to capture this ephemeral release of nitrogen, enhanced uptake capacity of existing roots was probably more important than development of new roots. Mycorrhizal infection was not affected by the water pulse treatments. However, since the water pulse only affected nitrogen availability and mycorrhizae are generally most effective in facilitating acquisition of less mobile nutrients such as phosphate, mycorrhizae likely do not play an important role in taking advantage of this opportunity provided by the pulse of water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004290705961
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  • 3
    Electronic Resource
    Electronic Resource
    Temporal dynamics of soil spatial heterogeneity in sagebrush-wheatgrass steppe during a growing season (1996)
    Springer
    Plant and soil 184 (1996), S. 299-309 
    Details
    ISSN: 1573-5036
    Keywords: Agropyron desertorum ; Artemisia tridentata ; nutrient availability ; resource patchiness ; sagebrush-grass steppe ; temporal variability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Variability in five soil resources essential for plant growth (NH4 +, NO3 -, P, K and soil moisture) was quantified using univariate, multivariate and geostatistical techniques in a sagebrush-grass steppe ecosystem at three times (early April, June and August) during the 1994 growing season. Samples were collected every meter in a 10 × 10-m ‘macrogrid’, every 20 cm within nested 1 × 1-m ‘minigrids’, and every 3 cm within additionally nested 15 × 15-cm ‘microgrids’. Strong autocorrelation for all variables in the three sample periods was only found over distances less than 2 m, indicating that patches of high internal uniformity in this soil were smaller than 2 m during the growing season. Differences in semivariograms between sample periods were most pronounced for NO3 -, NH4 + and soil moisture, variables that we consider to primarily limit plant growth in this system. The distance over which sample points were autocorrelated for NO3 -, NH4 + and soil moisture increased from April to June. In contrast P and K, which are relatively more abundant at the study site, exhibited relatively constant semivariance patterns over the three sample periods. Weak correlation was found between samples collected in the three sample periods for N and soil moisture indicating that the spatial pattern of these limiting resources changed between sample periods. However, P and K had highly significant correlations (p〈0.00001) among sample periods, indicating that the distributional patterns of these relatively more abundant resources remained rather constant. There were strong negative correlations between P and K and distance from the base of shrubs for all sample times (p〈0.001), indicating an increase in P and K close to shrubs. Similar strong negative correlations were not found between distance from the shrubs and levels of NH4 +, NO3 -, or soil moisture, nor for any soil variable and distance from perennial tussock grasses. Changes in patterns of nutrient and soil moisture variability within a growing season suggest that not only must plants acquire soil resources that vary in time and space, but that they may also have to adjust to different scales of resource patchiness during the season.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00010459
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  • 4
    Electronic Resource
    Electronic Resource
    Culture of pachytene spermatocytes for analysis of meiosis (1995)
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 16 (1995), S. 128-139 
    Details
    ISSN: 0192-253X
    Keywords: Spermatogenesis ; meiosis ; synapsis ; synaptonemal complex ; G2-M transition ; okadaic acid ; actinomycin D ; camptothecin ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: An impediment to the investigation of mammalian spermatogenic meiosis has been the lack of an appropriate system for experimental manipulation of meiotic prophase cells. We report here the use of a simple system for the short-term culture of pachytene spermatocytes. We have assayed parameters of cell function pertinent to meiotic prophase, namely chromosome pairing and synapsis. During the culture period of 24-48 hr, cells maintained typical pachytene morphology, chromatin condensation patterns, and chromosome pairing, as assessed by light and electron microscopy. Uridine incorporation, monitored by autoradiography, reflected the chromosomal distribution found in vivo in that the autosomal chromosomes were transcriptionally active, while the sex chromosomes were not. Thus features of chromosome pairing and sex chromatin inactivation are maintained in these cultures. We have conducted experiments to demonstrate that cultured pachytene spermatocytes can be useful for the analysis of agents, some of which may be suspected mutagens, that might affect chromosome structure and function during meiosis. Treatment of cells with actinomycin D revealed a differential effect on chromatin condensation in the autosomes versus the sex chromosomes. Carnptothecin, a topoisomerase inhibitor, induced desynapsis of paired chromosomes. Okadaic acid, a phosphatase inhibitor, induced premature metaphase-I condensation of pachytene chromosomes. This last experiment suggests that these cultured cells may be useful for analysis of meiotic cell cycle controls. Taken together, these results demonstrate a culture system that can be useful for analysis of meiotic events as well as in screening for potential mutagenic agents that might affect meiotic chromosome structure and function. © 1995 Wiley-Liss, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/dvg.1020160206
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