Soil CO2 efflux in a beech forest: comparison of two closed dynamic systems

The aim of this study was to understand why two closed dynamic systems with a very similar design gave large differences in soil CO₂ efflux measurements (PP systems and LI-COR). Both in the field (forest beech stand) and in the laboratory, the PPsystems gave higher estimations of soil CO₂ efflux than the LI-COR system (ranging from 30% to 50%). The difference in wind speed occurring within the soil respiration chambers (0.9 m s⁻¹ within the SRC-1 and 0.4 m s⁻¹ within the LI-6000-09 chambers) may account for the discrepancy between the two systems. An excessive air movement inside the respiration chamber is thought to disrupt the high laminar boundary layer over the forest floor. This would promote an exhaust of the CO₂ accumulated into the upper soil layers into the chamber and a lateral diffusion of CO₂ in the soil towards the respiration chamber. The discrepancy between the two systems was reduced (i) by decreasing fan speed within the SRC-1, (ii) by increasing wind speed over the soil surface outside the respiration chamber, or (iii) by using an artificial soil design without high CO₂ concentration in soil pores. We show that wind speed is an important component of soil CO₂ diffusion which must be taken into account when measuring soil CO₂ efflux, even on very fine textured soil like silt-loam soil. Proper measurement can be achieved by maintaining wind speed inside the chamber below 0.4 m s⁻¹ since low wind speed conditions predominate under forest canopies. However, more accurate measurements will be obtained by regulating wind speeds within the chamber at a velocity representative of the wind speed recorded simultaneously at the floor surface. This revised version was published online in June 2006 with corrections to the Cover Date.     

Comparative analysis of Cryptosporidium, Giardia and indicator bacteria during sewage sludge hygienization in various composting processes

AIMS: To evaluate the suitability of Clostridium perfringens, Escherichia coli and enterococci as indicator organisms for Cryptosporidium and Giardia in treated sludge. METHODS AND RESULTS: Occurrence of Cryptosporidium oocysts and Giardia cysts, detected and enumerated by direct immunofluorescence microscopy, were compared with counts of indicator bacteria during six different sewage sludge hygienization processes, including closed reactor and open windrow composting, and sludge sanitation by quicklime or peat addition. No statistical correlation existed between the counts of indicator bacteria, Cl. perfringens, E. coli, and enterococci and occurrence of Cryptosporidium or Giardia. In sludge end-products, Giardia cysts were detected more frequently than Cryptosporidium oocysts. SIGNIFICANCE OF THE STUDY: Direct analysis is the best method to confirm the presence of (oo)cysts in sludge.     

Differential responses of three fungal species to environmental factors and their role in the mycorrhization of<Emphasis Type="Italic"> Pinus radiata</Emphasis> D. Don

Three ectomycorrhizal (ECM) isolates of Rhizopogon luteolus, R. roseolus and Scleroderma citrinum were found to differ markedly in their in vitro tolerance to adverse conditions limiting fungal growth, i.e. water availability, pH and heavy metal pollution. S. citrinum was the most sensitive, R. luteolus intermediate and R. roseolus the most tolerant species. Pinus radiata D. Don seedlings were inoculated in the laboratory and in a containerised seedling nursery with spore suspensions of the three ECM species. Colonisation percentage was considerably lower under nursery conditions, probably due to competition by native fungi. The effects of nursery ECM inoculation on seedling growth depended on the fungal species. Only R. roseolus-colonised plants showed a significantly higher shoot growth than non-mycorrhizal plants. All three fungi induced significantly higher root dry weights relative to control plants. Despite the low mycorrhizal colonisation, mycorrhization with all three species improved the physiological status of nursery-grown seedlings, e.g. enhanced root enzyme activity, shoot nutrient and pigment content, net photosynthesis rate and water use efficiency. Of the three fungal species, R. roseolus was the most effective; this species was also the most adaptable and showed the greatest range of tolerance to adverse environmental conditions in pure culture. It is, therefore, proposed as a promising fungal species for ECM inoculation of P. radiata in the nursery.     

Seasonal Variation of Ichthyoplankton in a Western Caribbean Bay System

The plankton of Bahia de la Ascension was sampled monthly, from August 1990 to July 1991, to ascertain ichthyoplankton composition, abundance, and seasonality. These data were used to assess the inferred function of the bay as spawning and nursery grounds. Fifty-one families, 66 genera, and 53 species of fish embryos and larvae were identified. Engraulidae, Clupeidae, Labrisomidae, Callionymidae, Gerreidae, and Gobiidae comprised 81.5% of the larvae captured: the remaining 18.5% included several coral reef fish families. Greatest mean fish egg densities were recorded between December and April, 341–246 per 100m³, suggesting a major spawning period. The monthly mean density of total fish embryos and larvae showed two peaks: one in late dry season (June), dominated by newly hatched engraulid, and a second (December) during the cold-front season with high densities of preflexion labrisomid and engraulid embryos. When labrisomid and engraulid embryos and larvae were excluded, densities peaked in the rainy season (July to October). Gerreidae and Callionymidae were significantly more abundant in the rainy season, while Labrisomidae and Gobiidae in the cold-front season. The highest embryos and larvae richness was observed in August during the rainy season with mean value significatively greater than those from cold-front and dry seasons. The occurrence of high egg densities and the wide range of embryos and larva stages are evidences that Bahia de la Ascension is a regionally important spawning and nursery ground for marine fish. Because this study covered partially the marine ecosystem of Bahia de la Ascension using convential gear, we suggest to conduct further research for have a full understanding of the importance of this bay for fish recruitment.     

Food choice by older people: the use of semi-structured interviews with open and closed questions

Objective: To evaluate difficulty chewing, consequent food choice and impacts using both open and closed questions within a semi‐structured interview format. Design: A cross‐sectional study using a semi‐structured interview (SSI) with open and closed questions Setting: Independently living people in South‐West London interviewed in their own homes Subjects: A group of 54, edentate people (mean age 82, R= 60‐93 years) were studied. Results: Most subjects (69%) expressed difficulty eating at least one type of food, half were unwilling to eat the foods they found difficult, others were conscious of cooking longer or cutting smaller in order to manage these foods, although no one accepted that they overcooked food. There were dramatic differences in the number of subjects expressing difficulty to chew various foods when responding to open and closed questions. Roast beef proved a good discriminator in this group of predominantly English subjects. The importance of the questioning process was also shown by the discrepancy of responses between variously prepared apples and the inability of any subjects to bite an unpeeled apple. Conclusions: For sensitive appraisal of food choice it is obviously essential to assess relevant foods, for the culture of the group being studied. Open questions provide a way of exploring which are the appropriate foods and food preparation as criteria to assess perceived chewing ability and treatment benefit. The semi‐structured interview method is particularly valuable for the study of older people. Closed questions provide different information which is also necessary to secure recall by older people.     

Variation in Chromatin Structure of the rDNA Transcribed Region in Human Peripheral Blood Lymphocytes

The rDNA transcribed region (TR) was tested for its accessibility for RsaI recognizing 15 TR sites, DNase I, and photoinducible arylazide (N-(4-azido-2-hydroxybenzoyl)-N,N"-diaminoheptane acetate) in isolated nuclei, and for the arylazide in intact cells. Arylazide readily entered the cells and did not appreciably affect the chromatin structure. Its photolysis products efficiently modified DNA in accessible sites. Single-strand breaks made by DNase I were not transformed into two-strand ones in rDNA TR, suggesting the necessity of denaturing electrophoresis for such an analysis. About 70% of all rDNA copies proved poorly accessible for endonucleases and arylazide, the accessibility being higher in their 18S and 5.8S rRNA gene regions than in the regions of the external transcribed spacers (ETSs) and the 28S rRNA gene. Proteinase K disrupted this structure, and the corresponding copies were extracted from nuclei. This explained whyin situ hybridization occasionally fails to reveal rDNA in the nucleolar fibrillar center (FC) on electron microscopic preparations. In other rDNA copies, TR (excluding 5"-ETS) was accessible for nucleases and arylazide. These copies were not extracted from nuclei treated with proteinase K. Some of their RsaI sites were protected by tightly bound proteins. Seven such regions were identified in TR. Possible association of the molecular structure, nucleolar location, and functional state of rDNA is discussed.     

Coherent patterns of abundance and size of a tropical snapper in dynamic estuary systems

Although tropical estuaries are important juvenile habitats for the snapper, Lutjanus russelli, the extent of this utilisation, and relationships to physical variation are unknown. We used fish trapsto investigate spatial and temporal patterns of distribution, abundance and size of L. russelli within and between three tropical estuaries (Cattle, Barramundi and Alligator Creeks) over a two year period. L. russelli showed no indication of spatial segregation by size along the lengths of the estauries. The probability of capturing L. russelli was similar throughout Barramundi Creek and the seaward parts of Cattle Creek. However, the probability of capture fell markedly in upstream regions of Cattle Creek. These areas where characterised by depressed salinity levels due to seasonal flooding. High probabilities of capture of L. russelli during the wet and post-wet seasons in the whole of Barramundi Creek correlated with the time of smallest modal sizes. Thisreflected the entry of large numbers of small recruits into the trappable population. Temporal patterns in mean length were consistent for both years. The major feature of the size data was a clear pattern of seasonal change in the mean fork length of L. russelli, with largest mean sizes occurring in the pre-wet and the smallest mean sizes in the wet and post-wet seasons. This pattern probably reflected the interaction of four processes; the entry of new recruits into the trappable population, growth and mortality during residence in the estuarine nursery habitats, and migration of large fish away from the estuaries. The three creeks studied provided L. russelli with a harsh and extremely variable environment. Over the three creeks, salinities ranged from extremely hyposaline (0) to very hypersaline (55.5) and varied up to 39 within a location. However, despite the substantial physical differences and the spatial separation of the three estuaries, the patterns of temporal change were clear and consistent. Overall, the annual pattern of change insize seemed to relate more to biological processes of recruitment, mortality and migration than to responses to physical variability.