Biogeochemistry of billabong sediments. II. Seasonal variations in methane production

1. We examined the temporal (seasonal and diel) and spatial variation in methane flux from sediments of a billabong in south-eastern Australia, and related it to variations in the rate of organic matter decay, concentration of interstitial metabolites, and sediment redox. 2. Total gas ebullition ranged from <2 to >59mlm^?2h^?1, and was highest in the summer months when water temperatures were >25°C. These rates are equivalent to carbon fluxes of about 16–30gC—CH₄m^?2yr^?1. Ebullition was greater from unvegetated sediments than from sediments colonized by the emergent macrophyte Eleockaris sphacelata, R, Br. or the submerged macrophyte Vallisneria gigantea Graeb. There were no consistent differences in the rate of ebullition over the day and the night. 3. Methane accounted for about 42–45% of total sediment gas in the vegetated sediments, but about 60% in the unvegetated sediments. These ratios did not vary greatly throughout the year. Carbon dioxide was a minor component of sediment gas, usually comprising <5% of the total. Carbon dioxide contents were highest in summer, especially in unvegetated and E. sphacelata beds. 4. In vitro methanogenesis ranged from 3 ± 0.9 to 106 ± 30 nmol g(dry weight)^?1 h^?1, being highest in summer and lowest in winter. Added acetate (5mM) increased the rate of methanogenesis by up to 10-fold, with the effect being greater in summer than winter. Generally, added acetate had least effect in E. sphacelata sediments. The maximum rate of in vitro methanogenesis with added acetate was 243 ± 57 nmolg(dry weight)^?1 h^?1. 5. Ebullition was highly correlated with the rate of in vitro methanogenesis, with a rime lag of about 4 weeks. About 35–60% of benthic in vitro methanogenesis could be accounted for by ebullitive loss: the remainder was presumably lost via diffusion, flux through emergent plants or by oxidation. The rate of organic-matter degradation, assessed with amylopectin azure, varied throughout the year, but there was no clear relationship between ebullition and organic-matter decay. 6. Concentrations of interstitial ammonium, which also varied seasonally, ranged from 1 ± 0.2 to 13 ± 1 mgNl^?1. There was no clear relationship between ebullition rates and ammonium concentrations, Redox potential was most positive in the E. sphacelata sediments, but there was little consistent difference in the redox potential of V. gigantea and unvegetated sediments. Redox potential appeared not to be a controlling factor in methane release.     

Comparison of insects and vertebrates as removers of seed and fruit in a Western Australian forest

Removal from the forest floor of seed or fruit of the six commonest species of trees in upland areas of the northern jarrah forest of Western Australia was studied experimentally. The smallest seeds (Eucalyptus marginata, Allocasuarina fraseriana) were taken by insects (presumably ants). Heavier seeds or fruits (E. calophylla, Banksia grandis, Persoonia longifolia, P. elliptica) were taken more often by vertebrates (presumably srrmll mammals). Seeds of E. calophylla and B. grandis were most preferred by vertebrates, possibly because they have the highest relative concentrations of nitrogen and phosphorus.     

Early-season effects of supplemented solar UV-B radiation on seedling emergence, canopy structure, simulated stand photosynthesis and competition for light

Mixtures and monocultures of wheat (Triticum aestivum) and wild oat (Avena fatua), a common weedy competitor of wheat, were exposed to enhanced solar UV-B radiation simulating a 20% reduction in stratospheric ozone to assess the timing and seasonal development of the UV-B effects on light competition in these species. Results from two years of field study revealed that UV-B enhancement had no detectable effect on the magnitude or timing of seedling emergence in either species. End-of-season measurements showed significant UV-B inhibition of leaf insertion height in wild oat in mixture and monoculture in the second year (irrigated year) but not in the first year (drought year). Leaf insertion height of wheat was not affected by UV-B in either year. The UV-B treatment had no detectable effect on monoculture or total (combined species) mixture LAI but did significantly increase (5–7%) the fractional contribution of wheat to the mixture LAI after four weeks of growth in both years. In addition, the UV-B treatment had subtle effects on LAI height profiles with early season mixtures showing significant reductions in wild oat LAI in lower canopy layers in both years while midseason Year 2 mixtures showed significant reductions in wild oat LAI in upper canopy layers. The changes in canopy structure were found to significantly increase (6–7%) the proportional simulated clear sky canopy photosynthesis and light interception of wheat in mixture. These findings, and others, indicate that the effects of UV-B enhancement on competition are realized very early in canopy development and provide additional support for the hypothesis that UV-B enhancement may shift the balance of competition between these species indirectly by altering competitive interactions for light.     

Opisthosomal fusion and phylogeny of Palaeozoic Xiphosura

Fusion of opisthosomal tergites to form a thoracetron has previously been considered a characteristic of the xiphosuran superfamilies Euproopoidea Eller, 1938, and Limuloidea Zittel, 1885. Evidence is presented here that fusion also occurs in Bellinuroidea Zittel & Eastman, 1913. Results of a cladistic analysis of Palaeozoic xiphosuran genera indicate that Synziphosurina Packard, 1886, is a paraphyletic assemblage of stem-group Xiphosura. Superfamily Paleolimulidae superfam. nov. is erected for families Paleolimulidae Raymond, 1944, and Moravuridae P&íbyl, 1967.     

Reconciling landscape and local views of aquatic communities: lessons from Michigan trout streams

1. Rapidly advancing geographical information systems (GIS) technologies are forcing a careful evaluation of the roles and biases of landscape and traditional site-based perspectives on assessments of aquatic communities. Viewing the world at very different scales can lead to seeming contradictions about the nature of specific ecological systems. In the case of Michigan trout streams, landscape analyses suggest a predictable community shaped by large-scale patterns in hydrology and geology. Most site-based studies, however, suggest these communities are highly variable in structure over time, and are strongly shaped by site-specific physical and biological dynamics. As the real world is comprised of processes operating both at local and landscape scales, an analytical framework for integrating these paradigms is desirable.
2. Decomposition of variances by factorial ANOVA into time, space and time–space interaction terms can provide a conceptual and analytical model for integrating processes operating at landscape and local scales. Using this approach, long-term data sets were examined for three insects and two fishes common in Michigan trout streams. Each taxon had a unique variance structure, and the observed variance structure was highly dependent upon sample size.
3. Both spatially extensive designs with little sampling over time (typical of many GIS studies) and temporally extensive designs with little or no spatial sampling (typical of population and community studies), are biased in terms of their view of the relative importance of local and landscape factors. The necessary, but in many cases costly, solution is to develop and analyse data sets that are both spatially and temporally extensive.     

Protection, immune responses and side effects in Atlantic salmon (Salmo salarL.) vaccinated against furunculosis by different procedures

In an experimental trial lasting approximately 6 months, 10 different vaccination regimes against furunculosis were studied in Atlantic salmon pre-smolts. Single and repeated administration of vaccine by the intraperitoneal (i.p.), immersion or oral route, and revaccination by combinations of these methods, were tested. In challenge assays initiated 8 and 16 weeks after vaccination, fish injected once with a trivalent vaccine, and fish injected twice with a monovalent vaccine, both containing aluminium phosphate as adjuvant, were moderately protected. Non-injection vaccination protocols consistently failed to protect the fish. Compared with unvaccinated fish, protected groups showed elevated antibody responses toAeromonas salmonicidaantigens throughout the study. Increasedin vitroproliferation of head kidney leucocytes from i.p. vaccinated fish was found 16 weeks after vaccination. The use of a polyvalent vaccine preparation, and revaccination by injection or the oral route improved both immune responses and survival, compared to a single inoculation of monovalent vaccine. In all groups subjected to i.p. administration of vaccine, minor to moderate intraperitoneal lesions were found. In conclusion, i.p. administration of adjuvanted vaccine, preferably in a polyvalent formulation, is the optimal method of inducing anti-furunculosis immunity in Atlantic salmon, and is apparently necessary for an effective immunoprophylaxis of salmonid fish against furunculosis.     

Subgenus Systematics of Acanthamoeba: Four Nuclear 18S rDNA Sequence Types

ABSTRACT Classification of Acanthamoeba at the subgenus level has been problematic, but increasing reports of Acanthamoeba as an opportunistic human pathogen have generated an interest in finding a more consistent basis for classification. Thus, we are developing a classification scheme based on RNA gene sequences. This first report is based on analysis of complete sequences of nuclear small ribosomal subunit RNA genes ( Rns ) from 18 strains. Sequence variation was localized in 12 highly variable regions. Four distinct sequence types were identified based on parsimony and distance analyses. Three were obtained from single strains: Type T1 from Acanthamoeba castellanii V006, T2 from Acanthamoeba palestinensis Reich, and T3 from Acanthamoeba griffini S-7. T4, the fourth sequence type, included 15 isolates classified as A. castellanii, Acanthamoeba polyphaga, Acanthamoeba rhysodes , or Acanthamoeba sp., and included all 10 Acanthamoeba keratitis isolates. Interstrain sequence differences within T4 were 0%–4.3%, whereas differences among sequence types were 6%–12%. Branching orders obtained by parsimony and distance analyses were inconsistent with the current classification of T4 strains and provided further evidence of a need to reevaluate criteria for classification in this genus. Based on this report and others in preparation, we propose that Rns sequence types provide the consistent quantititive basis for classification that is needed.