Diversity and dispersal — Can the link be approached experimentally?

It has been hypothesized that the relative role of species dispersal in determining plant community composition and species richness changes along primary productivity and disturbance intensity gradients. Manipulative experiments with either diaspore addition or prevention are needed to validate this hypothesis. Due to methodological constraints, diaspore prevention experiments are rarely used. In the case of diaspore addition experiments, there are some potential sources of error. (1) Experiments may be confounded since patchiness of microbial communities is not considered and techniques equalizing microbial communities over study plots are not used. (2) The length of the period of observation may not be sufficient to understand whether the establishment of sown individuals was really successful. (3) The effect of the sowing treatment and the theoretical context of the whole experiment depends on the number and identity of species sown. When addressing the role of long-distance dispersal, it is almost impossible to say what the appropriate number and composition of species to be used for the experiment should be. (4) Until now, most of the attention has been on dispersal in space, while the role of “dispersal in time” (seed bank) has rarely been addressed. We conclude that stepwise accumulation of experimental studies, addressing the role of dispersal in shaping plant communities, will sooner or later reveal general patterns, given the experiments are well planned and aim to avoid the sources of errors described above.     

Der Beitrag des Tiefsee-Bohrprogramms zur Foraminiferen-Forschung

PalZ - The American Deep Sea Drilling Project (DSDP) with the deep-sea drilling vessel “Glomar Challenger” so far cored about 34 000 meters of sediment at more than 360 drilling sites...     

A modified distance variable for the Hill formalism for kinetic models of muscle contraction

The distance variable of the Hill formalism for kinetic models of muscle contraction is compared to a modified distance variable. Instead of measuring the distance from a fixed point on the myosin filament to a neighboring actin, the modified variable measures the deviation of the myosin cross-bridge from its equilibrium position. Although for attached cross-bridges the two definitions are equivalent, the new variable is an index of cross-bridge conformation for cross-bridges of all states. The modified variable may be used to complement the use of the Hill variable, or to replace it. The utility of the modified variable is illustrated by an example which matches cross-bridge structures to biochemical kinetic data and to the free energy functions necessary for the design of a kinetic model.     

X-Ray diffraction of oriented amylose fibers. I. Amylose dimethyl sulfoxide complex

The amylose–dimethyl sulfoxide complex has been investigated with the aid of x-ray diagrams of oriented fibers. The amylose occurs in a six-residue helix with alternate “up” and “down” chains packed in a square array, that is, pseudo-tetragonal. A unit cell is proposed with a = b = 19.21 A. and c = 8.12 A.     

Effect of calcium on the morphology of human platelets spread on glass substrates

The morphology of human platelets spread on glass substrates is sensitive to the presence of calcium. In the absence of Ca2+, cells spread from buffered salt solution develop radially oriented filopodia and subsequently a broad hyalomere surrounding the central region of the cell from which granules are frequently exocytosed. In the presence of Ca2+ cell rounding and apparent withdrawal from the substrate occurs. Scanning (SEM) and transmission (TEM) electron microscopy of cells rounded in the presence of Ca2+ show fibrous elements connecting the cells to the substratum as well as adherent to the substrate in the vicinity of the rounded cells. Interference reflection microscope (IRM) images of these cells are heterogeneous: some contain small discrete darker regions suggesting the presence of focal specializations at the ventral cell surface. In contrast IRM images of cells spread in the absence of Ca2+ indicate predominantly broad areas of unspecialized contact with the substrate in agreement with TEM observations. These results suggest that Ca2+ may enhance platelet-substrate adhesion by initially promoting the formation of focal specializations which become more pronounced as cell rounding occurs possibly due to Ca2+ activation of an actomyosin-based contractile mechanism.     

Environmental modulation of plant mycorrhizal traits in the global flora

Mycorrhizal symbioses are known to strongly influence plant performance, structure plant communities and shape ecosystem dynamics. Plant mycorrhizal traits, such as those characterising mycorrhizal type (arbuscular (AM), ecto-, ericoid or orchid mycorrhiza) and status (obligately (OM), facultatively (FM) or non-mycorrhizal) offer valuable insight into plant belowground functionality. Here, we compile available plant mycorrhizal trait information and global occurrence data ($\sim$100 million records) for 11,770 vascular plant species. Using a plant phylogenetic mega-tree and high-resolution climatic and edaphic data layers, we assess phylogenetic and environmental correlates of plant mycorrhizal traits. We find that plant mycorrhizal type is more phylogenetically conserved than plant mycorrhizal status, while environmental variables (both climatic and edaphic; notably soil texture) explain more variation in mycorrhizal status, especially FM. The previously underestimated role of environmental conditions has far-reaching implications for our understanding of ecosystem functioning under changing climatic and soil conditions.