TECHNIQUES FOR MEASURING VESSEL LENGTHS AND DIAMETERS IN STEMS OF WOODY PLANTS

Results were compared between the latex paint and compressed air methods for determining total vessel lengths, and between the sectioning and maceration methods for determining vessel diameters. The minimum, mean, median, and maximum vessel diameters were less with the sectioning method than with the maceration technique. Vessel diameter distributions were always nonnormal and had roughly similar patterns with the two techniques, but were statistically different from one another. In all six species where the paint and air methods for determining vessel length were compared, both methods showed a similar skewed vessel length distribution, with many short vessels and few long ones. Although there was no consistent pattern to the difference in results with these two methods, the vessel length frequency distributions were statistically different from one another. With the paint method, many vessels, especially many of the narrowest ones, were not paint-filled at the paint infusion port. The air method utilized the paint method, in part, and, in addition, is based upon the incorrect assumption that all vessels in the stem are the same diameter. Both techniques tended to exclude vessel lengths of the narrowest vessels. However, the narrow vessels, although numerous, contributed an insignificant amount to the total theoretical hydraulic conductance in stems.     

Pattern of cercarial emergence of Schistosoma curassoni from Niger and comparison with three sympatric species of schistosomes.

The emergence pattern of Schistosoma curassoni cercariae from Bulinus umbilicatus, whose adult worms parasitize bovine, caprine, and ovine ungulates in Niger, is of a circadian type with a mean emission time at 0855 hr +/- 1 hr 6 min, characteristic of the schistosome species parasitizing domestic or wild cattle. The comparison of this cercarial emergence pattern with those of the other 3 sympatric species of schistosomes (Schistosoma haematobium, Schistosoma bovis, and Schistosoma mansoni) shows a significant difference between the chronobiology of the cercariae infective for human and those infective for bovine hosts. This difference may improve epidemiological surveys based on snail prevalences by allowing the distinction between bulinids infected with human and bovine parasites.     

ROOT PRODUCTION IN FOUR COMMUNITIES IN THE GREAT DISMAL SWAMP

A sequential coring approach was used to measure root biomass and production over 1 year in four different communities within the Great Dismal Swamp. A second method, an implanted bag technique, was also used to measure root production, and values were generally lower using this technique. On all sites, fine roots were the most dynamic root component. Both biomass (1,887 g/m²) and production (354–989 g m ² yr^-1) were highest on the mixed hardwood site, the least flooded site, and second highest on the cedar site, the site with the longest duration of soil saturation (1,033 g/m² and 274–366 g m^-2 yr^-1). The maple-gum (696 g/m² and 59–91 g m^-2 yr^-1) and cypress (824 g/m² and 68–308 g m^-2 yr^-1) sites had similarly low amounts of biomass and rates of production. Environmental parameters that influenced production include frequency and duration of flooding, and soil type. Peaks in belowground production were observed on the most productive sites (mixed hardwood and cedar) in summer and late fall-winter; the other two sites exhibited little seasonal variability. The least flooded stand appears to allocate a greater percentage of net primary production belowground than the more extensively flooded stands. The ratio of above- and belowground allocation appears to change in response to a flooding gradient. This has major implications for ecosystem functions as carbon allocation patterns determine the array of litter types generated (leaves vs. roots) which affect decomposition rates and nutrient availability.     

A Rare, Larval-founded Colony of the Bryozoan Archimedes from the Carboniferous of Alabama

Very few basal attachments of the spiralled fenestrate bryozoan Archimedes are known. A newly discovered specimen is interpreted to have grown on a thin cylindrical ephemeral substratum that extended above the sediment-water interface, allowing paired spirals to develop and to extend in opposite directions when the colony was very small.     

Evidence for top predator control of a grazing ecosystem

The importance of top predators in controlling ecological processes in large, intact ecosystems is unclear. In grasslands that support abundant ungulates, top–down control by predators may be particularly important, because of the tight biogeochemical linkages of ungulate prey with plants and soil microbes. Here, I examined the effects of the recent reintroduction of the gray wolf Canis lupus on ecosystem processes in Yellowstone National Park, where herds of grazing ungulates previously have been shown to stimulate several processes, including soil net nitrogen (N) mineralization. Rates of ungulate grazing intensity and soil net N mineralization were compared before and after wolf reintroduction in grasslands ranging five‐fold in aboveground production. Grazing intensity and grassland net N mineralization declined after wolf reintroduction, a likely partial function of fewer ungulates; wolf predation has been one of several factors implicated in causing the decline in Yellowstone ungulates. In addition, the spatial pattern of grazing and net N mineralization changed after reintroduction. A shift in the spatial patterns of grazer‐associated processes is consistent with a growing body of work indicating that wolves have changed habitat use patterns of ungulates in Yellowstone National Park. These findings suggest widespread wolf effects on ungulate prey, plants, and microbial activity that have spatially reorganized grassland energy and nutrient dynamics in Yellowstone Park.     

Biochemical Evidence for Formate Transfer in Syntrophic Propionate-Oxidizing Cocultures of Syntrophobacter fumaroxidans and Methanospirillum hungatei

The hydrogenase and formate dehydrogenase levels in Syntrophobacter fumaroxidans and Methanospirillum hungatei were studied in syntrophic propionate-oxidizing cultures and compared to the levels in axenic cultures of both organisms. Cells grown syntrophically were separated from each other by Percoll gradient centrifugation. In S. fumaroxidans both formate dehydrogenase and hydrogenase levels were highest in cells which were grown syntrophically, while the formate-H₂ lyase activities were comparable under the conditions tested. In M. hungatei the formate dehydrogenase and formate-H₂ lyase levels were highest in cells grown syntrophically, while the hydrogenase levels in syntrophically grown cells were comparable to those in cells grown on formate. Reconstituted syntrophic cultures from axenic cultures immediately resumed syntrophic growth, and the calculated growth rates of these cultures were highest for cells which were inoculated from the axenic S. fumaroxidans cultures that exhibited the highest formate dehydrogenase activities. The results suggest that formate is the preferred electron carrier in syntrophic propionate-oxidizing cocultures of S. fumaroxidans and M. hungatei.     

Einfluß von Epicoccum nigrum,Alternaria alternata,Mucor racemosus und Ulocladium chartarum auf die Protozoenpopulation im Pansen des Rindes (in vitro)

The influence of moulded hay (Alternaria alternata, Epicoccum nigrum, Mucor racemosus, Ulocladium chartarum) and the efficiency of Vitamin B1 substitution to cope these effects on rumen protozoa was investigated using the longterm rumen simulation technique (RUSITEC) for about 25 days. Moulded hay affected medium-sized protozoa to a different extent (Alternaria alternata: ?16 %, Epicoccum nigrum: ?27 %, Mucor racemosus: ?9 %, Ulocladium chartarum: +2 %). The vitamin B1 substitution had positive effects during the feeding of Mucor racemosus and Ulocladium chartarum.     

Growth inhibition of putrefactive anaerobe 3679 caused by stringent-type response induced by protonophoric activity of sorbic acid

The inhibitory effects of potassium sorbate on the bioenergetics, phenylalanine uptake, protein synthesis, and certain aspects of cell regulation were examined in putrefactive anaerobe 3679. Undissociated sorbic acid appeared to act as a protonophore by lowering the intracellular pH and dissipating the proton motive force of the membrane. Sorbate inhibited the uptake of phenylalanine, decreased the rate of protein synthesis, and altered patterns of phosphorylated nucleotide accumulation, resulting in increased intracellular concentrations of GTP, ppGpp, and an unidentified compound (possibly pppGpp). The addition of a noninhibitory amount of tetracycline released the inhibition of growth by sorbate. Based on these results, we concluded that the inhibition of putrefactive anaerobe 3679 by sorbate resulted from a stringent-type regulatory response induced by the protonophoric activity of sorbic acid.     

Distribution of elements in rabbit liver lobule

The elemental composition of rabbit liver was determined by the PIXE and micro-PIXE methods. The mean concentrations of P, S, Cl, K, Fe, Cu, Zn, and Rb measured by both methods were similar. The latter method also allowed for localization of elements within lobule territory. It has been found that some elements are more prevalent in the veins (Cl, Fe) and others in the liver parenchyma (P, Cu, Zn). Moreover, Zn showed the characteristic intralobular distribution. Some methodological aspects of microbeam application to biological materials were also discussed.