Changes in plant species richness and productivity in response to decreased nitrogen inputs in grassland in southern England

Biomass production and plant species diversity in grassland in southern England was monitored before and after a change from conventional to organic farming. Our 18-year study, part of the UK's Environmental Change Network long-term monitoring programme, showed that the cessation of artificial fertiliser use on grassland after conversion to organic farming resulted in a decrease in biomass production and an increase in plant species richness. Grassland productivity decreased immediately after fertiliser application ceased, and after two years the annual total biomass production had fallen by over 50%. In the subsequent decade, total annual grassland productivity did not change significantly, and yields reached 31–66% of the levels recorded pre-management change. Plant species richness that had remained stable during the first 5 years of our study under conventional farming, increased by 300% over the following 13 years under organic farm management. We suggest that the change in productivity is due to the altered composition of species within the plots. In the first few years after the change in farming practice, high yielding, nitrogen-loving plants were outcompeted by lower yielding grasses and forbs, and these species remained in the plots in the following years. This study shows that grassland can be converted from an environment lacking in plant species diversity to a relatively species-rich pasture within 10–15 years, simply by stopping or suspending nitrogen additions. We demonstrate that the trade-off for increasing species richness is a decrease in productivity. Grassland in the UK is often not only managed from a conservation perspective, but to also produce a profitable yield. By considering the species composition and encouraging specific beneficial species such as legumes, it may be possible to improve biomass productivity and reduce the trade-off.     

Structural variability of C3larvin toxin. Intrinsic dynamics of the α/β fold of the C3-like group of mono-ADP-ribosyltransferase toxins

C3larvin toxin is a new member of the C3 class of the mono-ADP-ribosyltransferase toxin family. The C3 toxins are known to covalently modify small G-proteins, e.g. RhoA, impairing their function, and serving as virulence factors for an offending pathogen. A full-length X-ray structure of C3larvin (2.3 Å) revealed that the characteristic mixed α/β fold consists of a central β-core flanked by two helical regions. Topologically, the protein can be separated into N and C lobes, each formed by a β-sheet and an α-motif, and connected by exposed loops involved in the recognition, binding, and catalysis of the toxin/enzyme, i.e. the ADP-ribosylation turn–turn and phosphate–nicotinamide PN loops. Herein, we provide two new C3larvin X-ray structures and present a systematic study of the toxin dynamics by first analyzing the experimental variability of the X-ray data-set followed by contrasting those results with theoretical predictions based on Elastic Network Models (GNM and ANM). We identify residues that participate in the stability of the N-lobe, putative hinges at loop residues, and energy-favored deformation vectors compatible with conformational changes of the key loops and 3D-subdomains (N/C-lobes), among the X-ray structures. We analyze a larger ensemble of known C3bot1 conformations and conclude that the characteristic ‘crab-claw’ movement may be driven by the main intrinsic modes of motion. Finally, via computational simulations, we identify harmonic and anharmonic fluctuations that might define the C3larvin ‘native state.’ Implications for docking protocols are derived.     

Predators and avian community organization: an experiment in a semi-desert grassland

Summary We provide experimental evidence that predators are a major factor organizing a community of granivorous grassland birds (mostly emberizid finches). Our focus is not on the lethal effects of predators, but on the simple idea that (i) birds will not settle where they perceive a high risk of predation, and (ii) species differ in their perception of the safety of woody vegetative cover due to differences in antipredator escape behavior. Consistent with this idea is the fact that the composition of this grassland community responds markedly to minor manipulations in the distribution of woody cover. In particular, with the addition of cover to open grasslands, species with cover-dependent escape tactics increase in abundance, while the abundance of cover-independent species decreases greatly; this decrease may reflect aggression from cover-dependent species, but evidence suggests that some cover-independent species may actively avoid cover-rich areas per se. Non-predatory effects of cover, most notably those concerning food resources and microclimate, appear unable to explain these results. Predators may influence many communities of terrestrial vertebrates via species-specific responses to cover.     

A visually evoked escape response of the housefly

Summary Flies (Musca domestica) avoid danger by initiating a rapid jump followed by flight. To identify the visual cues that trigger the escape response in the housefly, we measured the timing and probability of escapes when the fly was presented with a variety of visual stimuli created by moving targets toward it. Our results show that an escape response is triggered by an approaching dark disk, but not by a receding dark disk. On the other hand, a bright disk elicits escape only when it recedes. A disk with black and white rings is less effective at eliciting escape than is a dark solid disk of the same size. This indicates that the darkening contrast produced by an approaching stimulus is a more crucial parameter than expansion cues contained in the optical flow. Escape is also triggered by a horizontally moving dark edge, but not by a moving bright edge or by a grating. An examination of several visual parameters reveals that the darkening contrast, measured from the onset of stimulation to the start of escape is nearly constant for a variety of stimuli that trigger escape reliably. Thus darkening contrast, coupled with motion may be crucial in eliciting the visually evoked escape response. Other visual parameters such as time-to-contact or target angular velocity seem to be relatively unimportant to the timing of escapes.Abbreviations P _s Probability of successful escape - r _disk radius of disk target - r _arena radius of shielding arena - v _disk linear velocity of disk target - v _edge linear velocity of edge - d _disk angular velocity of disk target boundary - _edge angular velocity of edge - _escape target distance at escape - d _start target distance before onset of target movement - h _edge height of the edge above fly - x _start distance from corner of triangle to start position of edge (0 or 50 mm) - x _escape distance from corner of triangle to the position of the edge when the fly escapes - x _center distance from corner of triangle to point above the center of the pad - x _total distance from the corner of the triangle to the base (height of triangle = base of triangle)     

Distribution of neurotensin-like immunoreactivity in rat and cat area postrema

The distribution of neurotensin-like immunoreactive (NT-LI) fibers and cell bodies in the area postrema (AP) of rat and cat, utilizing the peroxidase, antiperoxidase (PAP) technique, is described. In the rat, the greatest accumulation of NT-LI fibers were present along the borders of the AP, while there were very few NT-LI fibers in central regions. In the cat, scattered NT-LI fibers occupied the majority of the central AP, while moderate numbers of NT-LI fibers were present at the ventromedial border. In more rostral cat AP levels, the number of NT-LI fibers decreased. NT-LI somata were present in rat AP, but were lacking in cat AP. The localization of NT within the AP suggests that the cardiovascular and gastric effects attributed to NT may be mediated, in part, through the AP.     

The results of 2-year pollen monitoring of an urban network in Perugia,Central Italy

Continuous pollen monitoring of an urban network consisting of three stations has been undertaken for a period of 2 years in Perugia, central Italy. The aim has been to establish whether the Perugia pollen trap, active since 1983, is still representative of the area following recent urbanisation. Quantitative differences were found between the stations, reflecting different vegetational areas, but only slight differences were detected in relation to the timing of the principal period of pollination. Therefore, although individual pollen traps are necessary to characterize fully the different areas, one trap is sufficient to determine the key allergenic thresholds in the studied area.     

The results of 2-year pollen monitoring of an urban network in Perugia,Central Italy

Continuous pollen monitoring of an urban network consisting of three stations has been undertaken for a period of 2 years in Perugia, central Italy. The aim has been to establish whether the Perugia pollen trap, active since 1983, is still representative of the area following recent urbanisation. Quantitative differences were found between the stations, reflecting different vegetational areas, but only slight differences were detected in relation to the timing of the principal period of pollination. Therefore, although individual pollen traps are necessary to characterize fully the different areas, one trap is sufficient to determine the key allergenic thresholds in the studied area.     

Induction of an immune network cascade in cancer patients treated with monoclonal antibodies (ab1)

The antitumor effector functions of unconjugated monoclonal antibodies (mAb) in cancer therapy are not fully understood. Direct cytotoxic mechanisms such as antibody-dependent cellular cytotoxicity, complement-dependent cytolysis and apoptosis have been suggested. Induction of anti-idiotypic (ab₂) and anti-anti-idiotypic (ab₃) antibodies as well as the corresponding T cells (T₂ and T₃) has also been proposed to be of therapeutic significance. In this study induction of an immune network cascade in ten patients with colorectal carcinoma, treated with mAb 17-1A (ab₁) was assessed. After treatment, all ten patients had anti-idiotypic antibodies and anti-anti-idiotypic antibodies with ab₁-like binding specificity while only five of ten patients had T cells corresponding to ab₃ (T₃) as assessed by a proliferation assay (DNA synthesis), and an assay of interferon production (ELISPOT) (Enzyme-linked immuno SPOT) in vitro or by a delayed-type hypersensitivity reaction in vivo. Purified T cells from four of the five patients with a positive T₃ test responded with DNA synthesis after stimulation using human anti-mAb 17-1A anti-idiotypic monoclonal antibodies. These four patients had a clinical response showing a tumor reduction after therapy, while all six patients lacking a proliferative response failed to show tumor regression. Induction of a cell-mediated immune network cascade might accordingly be an important anti-tumor effector function of mAb and should be considered in the future design of mAb-based therapy protocols in cancer patients.     

用人工神经网络方法估计Ligistic方程参数

本文提出Logistic方程参数优化估计的人工神经网络方法,并选取一组标样进行具体尝试。结果表明,用这种方法估计Logistic方程参数效果极好。