Use of radial density plots to calibrate image magnification for frozen-hydrated specimens.

Accurate magnification calibration for transmission electron microscopy is best achieved with the use of appropriate standards and an objective calibration technique. We have developed a reliable method for calibrating the magnification of images from frozen-hydrated specimens. Invariant features in radial density plots of a standard are compared with the corresponding features in a "defocused" X-ray model of the same standard. Defocused X-ray models were generated to mimic the conditions of cryo-electron microscopy. The technique is demonstrated with polyoma virus, which was used as an internal standard to calibrate micrographs of bovine papilloma virus type 1 and bacteriophage phi X174. Calibrations of the micrographs were estimated to be accurate to 0.35%-0.5%. Accurate scaling of a three-dimensional structure allows additional calibrations to be made with radial density plots computed from two- or three-dimensional data

Biocrust Lichen and Moss Species Most Suitable for Restoration Projects

Reintroducing lichens and mosses to areas slated for restoration or rehabilitation may prove integral to project success by filling the biocrust component (niche) of arid ecosystems. In doing so, it is important to select appropriate species and genetic source material. Some bryophyte and lichen species are early pioneers and are potentially well‐suited for restoration projects. Species traits such as high reproductive rates, rapid establishment rates, and large asexual reproductive propagules can be beneficial for restoration. For instance, the large number of spores produced by some mosses are beneficial for reproductive success in arid environments. In addition to identifying the benefit of reproductive strategies, it is important to take habitat needs into consideration; lichen and moss species that are wide‐ranging both geographically and ecologically are recommended over geographically and edaphically restricted species that occur only in specific habitats, such as calcareous soils. Biocrusts used in specific restoration areas should have similar genetic source material (local provenance), and harsh environmental conditions should be ameliorated

Impacts of alien invasive plants on soil nutrients are correlated with initial site conditions in NW Europe.

Alien invasive plants are capable of modifying ecosystem function. However, it is difficult to make generalisations because impacts often appear to be species- and site-specific. In this study, we examined the impacts of seven highly invasive plant species in NW Europe (Fallopia japonica, Heracleum mantegazzianum, Impatiens glandulifera, Prunus serotina, Rosa rugosa, Senecio inaequidens, Solidago gigantea) on nutrient pools in the topsoil and the standing biomass. We tested if the impacts follow predictable patterns, across species and sites or, alternatively, if they are entirely idiosyncratic. To that end, we compared invaded and adjacent uninvaded plots in a total of 36 sites with widely divergent soil chemistry and vegetation composition. For all species, invaded plots had increased aboveground biomass and nutrient stocks in standing biomass compared to uninvaded vegetation. This suggests that enhanced nutrient uptake may be a key trait of highly invasive plant species. The magnitude and direction of the impact on topsoil chemical properties were strongly site-specific. A striking finding is that the direction of change in soil properties followed a predictable pattern. Thus, strong positive impacts (higher topsoil nutrient concentrations in invaded plots compared to uninvaded ones) were most often found in sites with initially low nutrient concentrations in the topsoil, while negative impacts were generally found under the opposite conditions. This pattern was significant for potassium, magnesium, phosphorus, manganese and nitrogen. The particular site-specific pattern in the impacts that we observed provides the first evidence that alien invasive species may contribute to a homogenisation of soil conditions in invaded landscapes. © 2008 Springer-Verlag.SCOPUS: ar.jinfo:eu-repo/semantics/publishe