Plant species diversity as a driver of early succession in abandoned fields: a multi-site approach.

Succession is one of the most studied processes in ecology and succession theory provides strong predictability. However, few attempts have been made to influence the course of succession thereby testing the hypothesis that passing through one stage is essential before entering the next one. At each stage of succession ecosystem processes may be affected by the diversity of species present, but there is little empirical evidence showing that plant species diversity may affect succession. On ex-arable land, a major constraint of vegetation succession is the dominance of perennial early-successional (arable weed) species. Our aim was to change the initial vegetation succession by the direct sowing of later-successional plant species. The hypothesis was tested that a diverse plant species mixture would be more successful in weed suppression than species-poor mixtures. In order to provide a robust test including a wide range of environmental conditions and plant species, experiments were carried out at five sites across Europe. At each site, an identical experiment was set up, albeit that the plant species composition of the sown mixtures differed from site to site. Results of the 2-year study showed that diverse plant species mixtures were more effective at reducing the number of natural colonisers (mainly weeds from the seed bank) than the average low-diversity treatment. However, the effect of the low-diversity treatment depended on the composition of the species mixture. Thus, the effect of enhanced species diversity strongly depended on the species composition of the low-diversity treatments used for comparison. The effects of high-diversity plant species mixtures on weed suppression differed between sites. Low-productivity sites gave the weakest response to the diversity treatments. These differences among sites did not change the general pattern. The present results have implications for understanding biological invasions. It has been hypothesised that alien species are more likely to invade species-poor communities than communities with high diversity. However, our results show that the identity of the local species matters. This may explain, at least partly, controversial results of studies on the relation between local diversity and the probability of being invaded by aliens.

An in-vitro evaluation of sealer placement methods.

Successful root canal therapy is dependent upon obturating the root canal system. A critical component of the filling procedure is sealer placement. This in vitro study investigated the efficacy of six methods of sealer placement using clear plastic blocks with simulated curved canals instrumented to the apex using a step-back technique. After sealer placement and setting, the blocks were cross-sectioned at 2 mm intervals from mid-canal to apex. The sections were evaluated with a stereo operating microscope at x6 magnification for placement of an evenly distributed layer of sealer around the prepared canal walls. The lentulo spiral and the Max-i-Probe Delivery System were the most effective means of sealer placement, followed by ultrasonic and sonic files. The least effective methods were the paper point and the K file.

Acute toxicity of aminoglycoside antibiotics as an aid in detecting botulism.

Gentamicin sulfate or neomycin sulfate injected intraperitoneally into 24- to 27-g mice at a dose of 6.2 mg per mouse elicited botulism-like responses in less than 30 min, but a dose of 3.1 mg per mouse had no observable effect. The normally nontoxic 3.1-mg aminoglycoside dose aggravated the illness induced by an earlier injection of Clostridium botulinum type A or B toxin; it was usually lethal in 2 to 20 min if the preexisting illness was moderate to severe and worsened the condition of mice for about 30 min if the preexisting botulism was mild. The aminoglycoside had no effect when given shortly after the botulinum toxin was injected intraperitoneally; the sensitized state followed a latent period. It rapidly produced botulism-like effects when given to mice which had responded to a mixture of botulinum toxin and another mouse toxic agent with an illness that did not include signs of botulism. An unexpected illness devoid of botulism-like effects was encountered during intestinal colonization of mice by C. botulinum. The appearance of botulism-like signs soon after 3.1 mg of gentamicin sulfate was injected supported other suggestions that this illness included botulism that was masked by the effects of a second cause.