Lepidium latifolium: plant nutrient competition-soil interactions

Exotic weeds are invading rangelands of the western United States at unprecedented rates. Understanding plant-soil relationships and competitive interactions of invasive weeds is crucial in long-term control strategies. In a greenhouse experiment, we investigated the influence of soil nutrient depletion on plant growth and plant competition between the exotic invasive weeds, Lepidium latifolium (invading wetlands) and Bromus tectorum (invading a multitude of habitats). Plants were grown individually and in combination until L. latifolium flowered, then roots and aboveground mass were harvested. Soil in individual pots was homogenized, subsamples collected for nutrient analyses, and the soil was re-planted to the same species, grown, and harvested twice more for a total of three growth cycles. As nutrient supplying capacity of the soil declined through growth cycles, aboveground mass of L. latifolium decreased significantly (PА.05) and growth potential of B. tectorum surpassed that of L. latifolium. Only bicarbonate-extractable soil ortho-P positively correlated with plant mass of L. latifolium. A separate experiment demonstrated that L. latifolium has a narrow window of soil water potentials for optimal growth; greatest growth at -20 kPa with significantly declining growth at saturation and -400 kPa. Our data suggest that L. latifolium primarily invades wetlands because the high soil water content reduces tortuosity and allows efficient transport of nutrients to this sparsely rooted species. When soil moisture and/or the nutrient supplying capacity of the soil declines, plants with greater root density can out-compete L. latifolium. Monocultural stands of L. latifolium may be self-limiting in time as available nutrients, particularly P, are biocycled to drier upper soil layers.     

Acrylamide formation from asparagine under low moisture Maillard reaction conditions. 2. Crystalline vs amorphous model systems

The formation of acrylamide was investigated in model systems based on asparagine and glucose under low moisture Maillard reaction conditions as a function of reaction temperature, time, physical state, water activity, and glass transition temperature. Equimolar amorphous glucose/asparagine systems with different water activities were prepared by freeze drying and were shown to quickly move to the rubbery state already at room temperature and a water activity of above 0.15. The acrylamide amounts were correlated with physical changes occurring during the reaction. Pyrolysis and kinetics of acrylamide release in amorphous and crystalline glucose/asparagine models indicated the importance of the physical state in acrylamide formation. In amorphous systems, acrylamide was generated in higher concentrations and at lower temperatures as compared to the crystalline samples. Time and temperature are covariant parameters in both systems affecting the acrylamide formation by thermal processes. On the other side, the water activity and glass transition temperature do not seem to be critical parameters for acrylamide formation in the systems studied.     

"Debye-Scherrer Ellipses" from 3D fullerene polymers: An anisotropic pressure memory signature

High-pressure studies on fullerenes have previously shown the existence of one- and two-dimensional (2D) polymerized C60 structures. Synchrotron radiation measurements, performed on C60 samples quenched from 13 gigapascals and 820 kelvin, yield unambiguous proof for the existence of a three-dimensional (3D) polymerized C60 derivative. Moreover, unusual ellipsoidal Debye-Scherrer diffraction patterns are observed, which shows that the giant anisotropic deformation induced by the nonhydrostatic compression is retained in the quenched samples. The multiple bonding possibilities of the highly symmetrical C60 allow the retention (down to ambient pressure) of the deformation, a phenomenon reported previously only under high pressure.     

Monocular spatial distortions induced by marked accommodation

Contraction of the ciliary muscle during marked accommodation causes the leading edge of the retina to advance as much as 0.5 centimeter. Near the posterior pole of the eye, the upward and downward extensional strains on the retina should be reasonably balanced. In the horizontal meridian an asymmetry is introduced because of the nasal location of the optic nerve head. Observers were asked to bisect the space between two parallel lines while fixating a movable line lying near the midpoint of the two lines. The test was conducted with the target far from and near the subject, in the horizontal and vertical meridians, and was repeated with accommodation paralyzed by a cycloplegic agent. Marked accommodation induced significant spatial distortions in the horizontal meridian. The effect is largely retinal.     

Transition From Sagebrush Steppe to Annual Grass (Bromus tectorum): Influence on Belowground Carbon and Nitrogen

Vegetation changes associated with climate shifts and anthropogenic disturbance have major impacts on biogeochemical cycling. Much of the interior western United States currently is dominated by sagebrush (Artemisia tridentata Nutt.) ecosystems. At low to intermediate elevations, sagebrush ecosystems increasingly are influenced by cheatgrass (Bromus tectorum L.) invasion. Little currently is known about the distribution of belowground organic carbon (OC) on these changing landscapes, how annual grass invasion affects OC pools, or the role that nitrogen (N) plays in carbon (C) retention. As part of a Joint Fire Sciences-funded project called the Sagebrush Treatment Evaluation Project (SageSTEP), we quantified the depth distribution of soil OC and N at seven sites experiencing cheatgrass invasion. We sampled plots that retained sagebrush, but represented a continuum of cheatgrass invasion into the understory. Eighty-four soil cores were taken using a mechanically driven diamond-tipped core drill to a depth of 90 cm, or until bedrock or a restrictive layer was encountered. Samples were taken in 15-cm increments, and soil, rocks, and roots were analyzed for OC and total N. We determined that cheatgrass influences the vertical distribution of OC and N within the soil profile and might result in decreased soil OC content below 60  cm. We also found that OC and total N associated with coarse fragments accounted for at least 10% of belowground pools. This emphasizes the need for researchers to quantify nutrients in deep soil horizons and coarse fragments.     

Identification and synthesis of 2-heptanethiol, a new flavor compound found in bell peppers

2-Heptanethiol was identified for the first time as a constituent of red and green bell pepper extracts. The chemical structure of this new aroma compound was proposed on the basis of mass spectra and retention indices and confirmed by chemical synthesis and nuclear magnetic resonance spectroscopy measurements. Its aroma properties were described as sulfury, onion-like, and vegetable-like, reminiscent of bell pepper at lower concentrations, with an orthonasal detection threshold of 10 microg/L of water. No differences in odor note and threshold value were observed for the enantiomeric forms, which were prepared from enantiopure 2-heptanol by tosylation, followed by thioacetylation and reduction, giving the target thiol enantiomers.     

Pilot study to evaluate the efficiency of insecticide-treated mosquito net fences for the protection of horses against nuisance insects in northern Brandenburg

A fence of black mosquito netting of 100 cm height, pre-treated with 80 mg/m2 of deltamethrin and UV-protected, was used to shelter horses from nuisance and biting insects on pasture in northern Brandenburg. The netting material was attached to the surrounding poles of the existing fences at a height of 15 cm above ground. Three trial groups were selected grazing in spatially separated areas with comparable densities of insect populations. One paddock was completely fenced apart from a wall of 170 cm height and 70 m length. The second pasture had only partial protection with 126 m (13.4%) of fence out of a total perimeter of 942 m. The third pasture served as control. Trap catches outside the fully or partially protected pasture were by at least 60% lower than those recorded for the control pasture. Digital pictures from five different anatomical regions indicated fewer flies on horses kept at the completely or partially protected areas as compared to the control area. The average attack rate in the protected areas amounted to 4.4 and 7.6 flies per horse at the completely or partially protected areas, respectively, as opposed to horses on the control pasture with 172.1 flies. In comparison to the control pasture the horses grazing on the protected areas showed fewer defensive movements, grazing in an undisturbed manner.     

Mineral Nitrogen in a Crested Wheatgrass Stand: Implications for Suppression of Cheatgrass

Cheatgrass (Bromus tectorum L.) is an exotic annual grass causing ecosystem degradation in western US rangelands. We investigated potential mechanisms by which crested wheatgrass (Agropyron cristatum L. Gaertn., Agropyron desertorum [Fisch. {Ex Link} Scult.]) suppresses the growth and invasibility of cheatgrass. Research focused on monthly mineral soil N availability and the proportional concentration of NH₄⁺-N in a crested wheatgrass community by microsite (crested wheatgrass, unvegetated interspace, shrub subcanopy) and soil depth (0–15, 15–30 cm) over a 1-yr period. Mineral soil N in crested wheatgrass microsites ranged from 0.24 to 1.66 mmol · kg^-1 and was not appreciably lower than the other microsites or other ecosystems we have measured in the Great Basin. The molar proportion of NH₄⁺-N in the mineral N pool of crested wheatgrass averaged over 85% for the year and is significantly higher than the other microsites and far greater than other plant communities we have measured in the Great Basin. We conclude that crested wheatgrass does not suppress cheatgrass by controlling mineral N below a threshold level; rather, we hypothesize that it may limit nitrification and thereby reduce NO₃^--N availability to the nitrophile cheatgrass.     

Cultivation legacies in soils after rehabilitation seeding in the Great Basin,USA

Integration of knowledge regarding impacts of historical cultivation on soils for restoration planning is limited even though these legacies can affect land productivity and future land uses for decades. Old fields are often actively transformed through restoration, afforestation, or rehabilitation seeding. Rehabilitation seeding with the introduced perennial grass crested wheatgrass (Agropyron cristatum) was employed on approximately 2 million hectares in the western United States, including old fields in the Great Basin desert region. Seeding continues to be the primary treatment in restoration today, yet a minimal amount is known regarding how the underlying cultivation legacies affect these soils over the long term. We studied sites where rehabilitation seedings overlapped old fields and adjacent noncultivated land to compare soil properties including soil texture, pH, soil organic carbon (SOC), nitrogen (N), and C:N ratios. Because these sites were identical in all aspects except former cultivation, our approach allowed us to test the hypothesis that cultivation legacies can be detected in the soil today and explore which soil properties most strongly reflect cultivation legacies using discriminant and principal components analyses. Discriminant analysis separated soils between the two land-use conditions with 95% confidence at all four sites. Of the six soil properties, SOC, N, and C:N ratios were most important for distinguishing the cultivation legacies at three sites, whereas soil pH was most important in one site. These results show that soils remain altered in these formerly cultivated sites even after being reseeded, suggesting that future productivity and management will also be affected.